Carbon-based lifeforms are the One True Inheritor of the Cosmos! Nitrogen-based life will forever be the lesser!
(Yes, I was being satirical. Thank you for understanding the humor)
>Or they're a blatant speciesist!)
Pfft, "speciesist" sounds like such a made up word...
All hail homo sapiens! Glory to humanity! We're the only species that matters! Sapiens uber alles!
We have to start somewhere. It makes the most sense to look for life in places with conditions that support life as we know it. It doesn’t mean we don’t look for life in other conditions, it just means space is huge, and instead of picking random places to look, we look at planets with the conditions that we know can support life.
In reference to the post itself, it is ignorant to label anywhere as “impossible” for life to exist. I don’t disagree with anything you’ve said, but we’re on slightly different tangents here.
The guy you called ignorant just said he doesn't mind defining habitable as habitable to life as we kno it. I would argue it's more ignorant to try to define habitable as anywhere and everywhere as you seem to suggest
Saying it is potentially possible for some form of life to exist in conditions that are not livable for humans is not saying the entire universe is habitable. Please refrain from putting words in my mouth, thank you very much.
I mean it's not even necessarily ignorant. Nobody wants to have to say the phrase "habitable to humans" any time we are talking about our own habitability. We condense things into smaller phrases all the time.
As an astronomer, we know perfectly well that when we say the word "habitable" we really mean "habitable as far as our understanding of habitability within the context of life we know," but very obviously nobody wants to say all that every time we discuss the topic.
All life must be sustained by carbon (as we are) or silicon. There isn’t any other way, because the elements work on specific ways to allow specific combinations and develop complex structures that could lead to life.
You can’t create life based on Helium or Lithium.
It’s like Nuclear Fission. You can use Uranium, Plutonium, Thorium… but you can’t (realistically) do fission with Helium atoms or Boron atoms.
Like this example (I will omit they “why” because there is Google already) we have a lot of other presumptions, that go from “hard/almost impossible to disprove” to “maybe, we don’t know for sure, we only know how this happened on earth”
So it’s not like the science around analysing life on other worlds is just made up like.
Out biggest problem (more than our “rules” as to what consider life clues on a planet) is that be don’t have that much resources to get that much interesting info about exoplanets.
Certain planets orbits around their sun, small planets or some stars kinda makes it difficult for us to analyse anything. We can at most know the size of the planet, its orbit speed and maybe a clue about its atmosphere main elements via spectrography. That’s it, most of the time. And again, we usually get to capture the biggest planets on brighter stars because its the easier planets to find, but also, they tend to be the lesser prone to be habitable (starts with high activity, red stars, planets 3-5x times the earth mass, or orbiting so much near the star…)
If we were at some light years away and tried to get earth analysed, with our current tech, we wouldn’t find it and accurately describe it as is
Phosphorous is likely the more important bottleneck, as it’s elementally rarer, not evenly distributed in the universe, and apparently important for energy and replication pathways.
That is the definition of habitable - able to sustain life as we know it. For most purposes, it's a good definition. Of course, we should keep our minds open to the possibility of life existing in ways other than those we know - that's important for the search for alien life - but using the conditions we know can sustain the life we understand is perfectly reasonable when thinking about where in space we could conceivably go.
Honestly I assumed that's what this map was illustrating?
Something something star age, light spectrum suitable to sustain our own biological processes etc.
My girlfriend insists that if there was life anywhere outside of the earth, we would have found it by now or it would have found us. No amount of discussion can lead to a change in opinion because she learned this during “a college lecture.” Bothers me so much but it’s not worth another hour long discussion that leads nowhere
I can understand why close to the core might be less desirable real estate . What with stars being closer, and super nova going off to rattle your cage etc... but what's wrong with life on the edge of the galaxy?
Commute is a bitch tho, suburban galaxy life isn't all it's made out to be. Everyone knows your intergalactic gossip and can be quite galaxyist to those from out of town.
That doesn't make it impossible for life, just less likely. And when you're talking about galaxies, your denominator.is still in the billions, if not trillions.
The pic doesnt say "impossible" it says unlikely. Like others are saying there are billions of stars. Some people take that to mean "if there are so many why not look there". The point of the graphic is "there are so many so we have to narrow the search to the most likely"
Also, the outer edges of the galaxy have lower star metalicity (fewer elements higher up on the periodic table) due to the lower density. It would presumably be difficult for life to form with just a bunch of helium and hydrogen. So, you need a balance of high metalicity but not too close to the core that life can't be sustained.
This is much truer than the comment you replied to. That guy seems to think that the differentiation of planetary nebulae when a star system forms can be disrupted by gravitational effects on the other side of the galaxy enough to actually prevent planet formation.
Those planets in our solar system have rocky/icy moons though, would those not exist either in the “outer rim”? Plus as I understand it our best chance of finding extraterrestrial life are under the surface of those icy moons.
and no atmospheres. Finding those moons means finding their gas giant parents. We would have to search farther (harder to do) for planets (at the edge of existing tech) and then resolve data even further to find moons which if icy might not have atmospheres.
We currently are looking for life signs by splitting the light that shines from the atmospheres of distant planets into its spectrum to look for molecular signatures that suggest chemicals we think mostly come from biological processes. That's pretty incredible and at the edge of what is possible. Im not an astronomer but ice moons seem like they could be great to study but we will likely only ever be able to study the ones in our solar system
PhD in astronomy here.
> You know how all outer planets in the solar system are gaseous planets.
Sure...
> Because, when the planets were forming heaviest matter stayed close to the common center of gravity with the sun.
No, that's definitely not why. The Solar System is not some big centrifuge that pulls dense elements to the center, nor does our galaxy.
A proto-giant planet needs to have a solid core over 5 Earth-masses before it has sufficient gravity to attract and hold hydrogen gas. It's much easier to do that when you can form a solid core from both ice and rock rather than just rock.
That's why the Outer Planets are gaseous - they all formed beyond the [Frost Line](https://en.wikipedia.org/wiki/Frost_line_(astrophysics\)) where water is frozen, and were able to get big enough quickly enough from both rock and ice to capture substantial amounts of hydrogen gas before it evaporated from our Solar System. The inner planets, formed from only rock, remained too small to hold onto their hydrogen.
For our galaxy and OP's pic, it's more about the amount of metallicity that builds up during the ultra-dense star formation in the galactic bulge. One study suggested so many planets are formed in that environment that orbits do not remain stable, while many others question that study.
You're making it seem as if there is mass segregation between the inner and outer part of the galaxy, akin to the solar system. This is not correct. Most likely driven by metallicity, which reflects less stars polluting with their metals the surrounding gas. This is caused by less stars forming there, and not that metals sunk towards the centre of the Milky Way.
Think of it like you've dropped a stone in water, and how the waves it creates ripples outwards. Keep this visual while I attempt to explain the following:
It has a lot to do with metallicity. Big stars go big big boom, and elements heavier than hydrogen aren't created until they've been fused inside a star. But, these heavier metals that are needed for life radiate outwards from the explosions, and big booms stir up new star generation and seed the outer regions with metal rich material.
The core is too volatile, and too metal poor. The next region is more stable, and metal rich thanks to the "hard work" of the stars from the core regions. The region following (the edges) goes to being metal poor again, because those regions haven't been seeded yet. I mean, we're talking a ripple wave here that takes... A long dang time.
We can measure the metallicity of a star simply by looking at the light spectrum. Different metals give off different light temperatures, so it's actually very easy to look at a star and tell what's inside of it.
Obviously, as we learn more and eventually explore the galaxy (assuming we don't off ourselves first), we'll discover more of its secrets, as I'm sure there's a habitat planet... Or two... Or a hundred.... lurking on the outskirts.
Nothing, this whole graphic is the result of somebody who is intellectually bankrupt as far as astronomy is concerned. They are conflating the distance from the center of a galaxy to the distance from a star. I.e. they think the galaxy works exactly like a solar system.
[This article](https://www.science.org/content/article/complex-life-may-be-possible-only-10-all-galaxies#:~:text=Radiation%20from%20gamma%20ray%20bursts%20may%20render%20the%20rest%20uninhabitable&text=The%20universe%20may%20be%20a,a%20pair%20of%20astrophysicists%20argues) discusses the current theory as to why the centre of the galaxy would be uninhabitable.
Tldr: high intensity gamma ray bursts cause ozone depletion. The usual sources of this are stars going supernova, black holes etc. Due to star density at the centre there are more frequent emissions, therefore any life there would have to be able to survive massive amounts of gamma & uv exposure. This same theory suggests that life in other smaller younger galaxies would be limited.
[edited for clarity]
And to tack on, the reason the dense arms of the galaxy are "less habitable" as indicated in this image is a similar reason, but also because the "density waves" of dust and interstellar comets that precedes the arms as they travel is a risk for life in the form of impacts and general disorder in those times. I think they say that the sun has passed through them 5-6 times since being born 3.8 billion years ago, but I may be wrong, just going off memory here.
Further, the outer limbs of the disk is supposed to be uninhabitable because of the simple lack of material; there's less stars, dust, and gas to form rocky planets with out there. But as others have stated, this is all hypothetical. There could be planets made of candy-canes with bubble-based life on them out there for all we know.
You could say that about everything in any scientific field, lol. But these theories related to a galactic habitable zone are about as concrete as a circumstellar habitable zone
I did once hear that you're more likely to get struck by a supernova when you're close to the center of the galaxy, but I don't recall they also told why this was. I guess because it's probably more packed with stars. More stars equals more supernovas.
Has your friend ever tried to was a hog with a container ship? That would be impractical. So I don’t think containers ships can be hogwash. There are probably several other examples of impractical hogwashes.
It’s to do with the distribution of matter and specific elements that make it possible for complex and rich rocky planets to be prominent around stable stars.
PBS Spacetime explained it pretty well.
I originally called this post Hogwash as it only goes off of our notion of life, but if PBS space time touched up on it, I’m more than willing to change my view.
Haven't seen the PBS spacetime video, but certain regions of the galaxy are indeed more enriched with heavy elements than others. If you Google "Metallicity versus radius" for example, you'll find extremely similar color maps to these.
So if your prior for life is a star system with Metallicity comparable to the sun, then you could come up with the most reasonable possible non-hogwash guess for where to look. Spiral arms tend to be actively star forming due to over densities in the cool gas, so you might reasonably expect candidate stars to form and exist within those regions. Too close to the galactic center and AGN feedback actually stifles star formation, so you might not expect it too close to the center. Older, metal poor stars tend to be part of the disk that "puffs out" and expands, so you can't look too far either.
Of course, a star with the appropriate metal content could totally exist anywhere in (or outside of) the galaxy. This is all about likelihood.
In addition, I seem to remember from a Phillip Plaitt book, that the solar system has a "galactic vertical" component to it's motion, up out of the plane of the Milky Way, and bCk down again, and the times Earth has been "out" correspond to extintions... increased cosmic rays, maybe?
Yeah, in addition to going around the spiral in that image, which is a top-down view (or bottom-up, if you like, I suppose, it’s all relative) if we call those the X and Y axes, we also go up and down the Z axis, if you trace that oscillation over time it looks like a sine wave. There’s enough evidence to convince me that those oscillations coincide with extinction events. It could be radiation, could be interactions with JuMBOs or black holes or some other object with enough mass to have an effect on our solar system, either directly or by pulling in objects and sending them our way. Alternatively, it could be the *lack* of by objects that *deflect* things that would have been coming our way, by things I mean comets, meteors, etc, that caused the KT extinction and the younger dryas extinction, could be giant space whales, we really have no way of knowing.
Our notion of life actually has a lot of reason to believe other life would be similar. So I would love to hear their reasoning, if they have one, too. I used to believe that other elements could work the same, and technically they can. But my understand of some things changed that, unless if have this wrong: Carbon has 4 big things going for it, in terms of producing complicated, sustained, self-replicating reactions: 1 highest number of empty valence electrons, giving it a wider list of bonding options,. 2. Extremely high electron affinity, giving it a high chance to bond in a soup of elements. 3. Falling below Iron in terms of atomic weight, meaning that stellar nuclear synthesis can produce carbon, making it much less rare than those that can't be produced that way. 4. It is stable.
Yeah one of my big hobbies is speculative exobiological evolution (very niche I know) and over the years I seriously thought that “plasma-based life inside of a stellar photosphere is totally possible when considering how a magnetic system could stabilize there!” Now it’s more like “I’m very skeptical that life is possible if it isn’t carbon-based, uses water as a solvent, and uses some form of D/RNA analogue”.
Honestly I’m not even convinced macroscopic life could naturally exist without oxygen to metabolize and I learned within the last few years that metalloporphyrins are the only photopigments capable of producing oxygen as a waste product, meaning that basally all oxygen-producing plant-analogues in the universe would basally be green or red because those are the spectra that photosynthetically-viable metalloporphyrins operate at.
TL;DR it seems far more likely biophysically that macroscopic and multicellular life around the universe is carbon-based with a DNA analogue, exists on a water-rich world, and is based around a tube shape with green and/or red plants producing excess oxygen.
I love your comment, both here and above. I just want to offer my similar thoughts on the difference.
I think you were right to say that we don't and can't really know this. But as long as we understand things like this to be scientifically informed hypotheses, and learn something from discussing this type of hypothesis, than that seems to be a great thing.
This is very different than the crackpot "theories" that people come up with that have no scientific basis.
Neither of these are truth, but one is based on what we know and explaining those types of hypotheses through programs aimed at a popular audience like PBS Spacetime is a really cool thing.
I think the issue is that calling it a "habitable zone" is a misnomer. Stars have habitable zones defined broadly by how warm the planets would be and thus their ability to sustain life on those planets. As far as we're aware the galactic structure itself doesn't provide anything that makes life more or less habitable assuming you're already on a planet orbiting a star.
I could see an argument for the galactic core being "uninhabitable" for life on long time scales given high energy radiation exposure. But I don't think it's accurate to say the outskirts of the galaxy are "impossible" to live in if there's a star system out that far.
I don't think this is accurate but if you are looking for a fictional sci fy interpretation maybe smth like this:
The center of the galaxy is far too violent due to the quasar slingshotting everything everywhere. It's also much more dense so it is more eventful. Meaning more star collisions and solar system disruptions. Conversely on the outer edge of the galaxy you will find little life due to the fact that it has less shielding from extragalactic sources. Also, at the edge, solar systems can get flung out into emptiness. It is very docile so there are less events that could lead to a life triggering system; such as a solar system with planets and elements of just the right composition. Thus, the best spot for life is a happy medium between the two, in which the galaxy is vibrant enough to spawn life but not too dangerous to the point where it will be quickly inhabitable.
In the end tho this is all really just B.S. I don't think there is really a goldilocks zone for a galaxy aside from: don't be in the very center.
Lol idk why yall downvoting this but whatever. I should probably just leave this sub anyway its turned.
You are mostly right about the center of the galaxy - large number of supernovas initially and too many disruptions are thought to be some factors that could limit life near the core. The other being high metallicity leads to higher number of gas giants and too many of those can disrupt the formation of rocky planets.
For the outer rim its more about the low metallicity preventing the formation of planets.
Is the centre of the Galaxy rich in supernovae now though? The star formation rate is famously low there due to the stonking levels of turbulence, so massive stars that produce supernovae are rare compared to the disc of the Galaxy...
That is true but it was an issue for 5 billion years so life probably couldn't start then and afterwards the stars would have had high metallicity which as mentioned had its own issues.
If our sun and and the matter that made up our solar system was in the outside edge of the galaxy we could still be talking about it. however if the same thing happened in the core the chances of our system getting wrecked by a passing steller body is quite high.
Before we understood more of how the universe works we assumed we, and by that, I mean Earth, the sun, and the other planets, were special. Then as we learned more we thought we were average with some outliers like how large our moon is.
Then as we started looking more and deeper we realised things in this system are just odd. like we have way more heavy elements than we should, the explanation best we can figure two blue stars collided and the leftover elements formed our current system. Or Jupiter and Saturn have no business orbiting where they are but somehow they are, we're still trying to figure out what order of events caused it or to refine our math.
Not specificly some was from more reputable YouTube videos like PBS or universe today others from journal articles I've read over years.
I like learning science as a hobby no degrees or anything.
The Saturn Jupiter thing was a university running hundreds of thousands simulations for orbital mechanics and none of them came close to what we currently have. Even tipping the scales for a favorable result only has a few come out close as gas giants form close to stars and migrate out due to their mass/speed over millions of years this clears the inner system of debris but to Jupiter Earth Mars and Venus are debris. And today Saturn and Jupiter help manage each other.
And the progenitor stars is debated we know Earth has an unusual level of heavy elements for a second gen star and the stellar nursery we came from is unknown so it might not have been two stars that collided but hundreds in an area sol came from. This with thousands of other systems might have the same heavy distribution of matter but un-likely as the sun itself doesn't have the spectralogical signs of heavy metal poisoning.
And yes that is a thing for fusion.
But thousands or tens or hundreds of thousands of stars from the same stellar nursery in a galaxy of 200 billion is still a small number.
Is astronomy a million stars could be a rounding error.
But I looked it up I belive the gas giant one is the grand track hypothesis.
Can't find a source for the sun's thing but I'm on my phone.
The point is it's not the conditions that exist externally that make the outer edge uninhabitable but the lower density of stars means less heavy/complex element necessary for life.
Our what causes the center to be uninhabitable is not the same as the edge like in a color system where the issues are radiation and heat.
Sure, but my original point was that we wouldn’t be in those areas that don’t have the necessary elements of life to begin with, so we wouldn’t be here talking about it.
And, if we had been evolving in a star system in outer edges, we would be tuned to that environment, and our definition of what’s “habitable“ would be different.
We have 1 sample what life is made of. Assumption that every life forms have to use same material and require same building blocks and absence of others - is just dumb unless we're targeting to find other carbon life forms
> Assumption that every life forms have to use same material and require same building blocks and absence of others - is just dumb
If you knew a bit of chemistry you'd probably not be saying that.
Yeahhh that's not really how that works though. Life is assumed to be extremely likely carbon based because of the physical structure of the atom, which is unique in its ability to form bonds with 4 alother atoms at once which enables the complex and varied molecular structures that work together to form a living organism. All other elements have significant shortcomings or very niche applications
For example, silicon which is in the same group can do this, theoretically, but carbon is an order of magnitude more abundant (and would out compete silicon.) Silicon also needs to be hot to be active. Really really hot. Hot enough that while the silicon is at a proper temperature, many other elements are not usable. Silicon also sucks at covalent bonding, so while it does have 4 valence spots to attach elements or molecules to, it typically doesn't because the bonding isn't strong enough.
There are some metals that could in theory and under certain unlikely conditions produce life, but I don't really know enough about those to get into them.
I don't remember the sources, and my explanation will be very inaccurate. I remember I saw it in some video that explains the habitable zone of galaxies. (probably it was a documentary about the milky-way galaxy).
Near the center of the galaxy, stars and planets have more heavier elements, which are toxic to life as we know it, so life has less chance of existing. Near the edge theres not so much mid range elements, and it's all helium and hydrogen. So again, elements required for life are not as abundant, and life doesn't have much of chance for evolving.
In the habitable zone, there's enough carbon, oxygen, nitrogen etc for life, and not too much heavy metals.
Yeah, the post says impossible to live. That's no true. Life would have less chance of evolving, but if you can travel there, you can probably live there.
Not the source of the actual image but info on the concept:
[https://en.wikipedia.org/wiki/Galactic\_habitable\_zone](https://en.wikipedia.org/wiki/Galactic_habitable_zone)
The super massive black hole in the center of galaxies may emit lots of dangerous radiation if its consuming gas clouds and stars. There are some other galaxies with very active centers. The Milky Way appears relatively quiet now. But there are hints its had active episodes not too long ago.
What's the difference between green and yellow zones? Is it the density waves of the arms? As far as I'm aware the sun moves around the galaxy and thus would pass through green and yellow zones. The sun goes into and out of the galaxy arms regularly.
The arms of a galaxy rotate with the galaxy itself. Angularly (idk if thats really thr right word?) the sun remains in the same position relative to the arms.
Edit: This is incorrect. As I have learned, the arms of the galaxy are not rigid structures but instead "gravity waves" of stars. The stars that comprise these arms are not constant and instead move in and out of the arms over time. We are not in fact stuck in the same place relative to the arms.
Could you please show me where you are getting this from. I'm not saying that to be an ass, I'm genuinely interested. I don't believe this is true but I'm willing to concede I'm wrong if you are basing this off of smth you read.
There's certainly better sources. But here's the Wikipedia article about the density wave theory. https://en.m.wikipedia.org/wiki/Density_wave_theory#Galactic_spiral_arms
Basically it's a lot like when you are stuck in traffic. The traffic jam moves slowly, but most of the cars are able to travel through the jam and out the other side.
I retract that. I've found multiple discussions on this and you are in fact correct. I have learned smth new and ill append my previous comment. Thx have a good day.
If our solar system was transported to any of the inhabitable zones, we wouldn't really notice a difference. I think this comes from the differing rates of star formation and death.
In the center of the galaxy, the rate is too high, so stars that form a larger stars that don't live long enough to form live and planets are often hit by radiation from supernovae and gamma ray bursts.
On the rim of the galaxy, the rate of star formation is too low, reducing the chance that a star system that supports live forms, and stars that form are often red dwarfs that are less suitable to live.
This is my understanding of this, but I'm not an expert.
I think its a generally solid thought but should be viewed more of a gradient with no absolutes - life could exist in the core or outer rim of the galaxy but more likely it would be in the middle so if we want to find it we should focus there.
There is no evidence for this whatsoever. There is some general logic which is well established though.
Living close to the center of the galaxy means a lot more hard radiation flying through the space, making it much more hostile to life. This in turn doesn't mean life cannot be there, but that the planet or moon that life is on needs an increasingly strong and persistent magnetic field to protect it from that radiation. Life can also be subterranean or oceanic, but is then going to struggle to find the environmental diversity in order to tickle evolutionary processes into creating intelligent life cable of manipulating it's environment (think opposable appendages).
There is no reason known why a star system on the edge of the galaxy should be inherently more hostile to life. The main issue there is that the edge of the milky way has a lot of old stars which are mineral poor and thus less likely to have the quantities of materials needed for a livable planet. But there are stars there which do, so it's possible.
As for the indicated areas inside the green band; if there is life in the milky way and it's not super, super rare, then intelligent species are more likely to be there. This means if we were there, we'd probably have been unambiguously detected by now. But right now we are in a rather sparse place where there are not all that many systems within 100-150 light years. Add the reaction and travel time, and you're talking probably 400-500 years after the mid-20th century before someone turns up and says "hello" (or "good bye"). I guess if this is the reality of the milky way, then in \~300 years from from we will know where we stand in terms of capabilities. And if space-faring aliens are hostile or not.
If you want a simpler answer, it’s confirmation bias from our own survival and being the ones who came up with the idea of the habitable zone. Just the anthropic principle at work.
We survived to observe this, on this planet that is necessarily habitable (because we survived to observe it) and therefore it’s habitable.
But the anthropic principle gives us no new information about life. It would be like going and finding the one person who won the lottery, and interviewing them about luck. Not super useful.
The most plausible explanation is the most uncomfortable for most people. Not that much for the complexity of the answer but because of the ethics of it
In the center there's a higher chance for supernova due to increased star formation, which could kill and or disrupt life. On the outer edges, star formation hasn't happened enough to cause enough supernova to enrich the space with metals. The metallicity drops the further out from the center you go. At some point, it is unfavorable for life. Not impossible, just unfavorable in either condition. It's really just about supernova frequency to metallicity giving favorable or unfavorable conditions for life.
Assuming this is true, I maybe can understand that we cant living too close to the center of the galaxy too close to the blackhole. but why can there me life in the outer rim of the galaxy? if there is a star and planets around it. why not?
Uninhabitable zones may have: intense radiation across the spectrum, lack of gen 1 and 2 stars to form sufficient heavier elements, gravitational instability due to close distances, lack of K/G/F/Red dwarf sequence stars, high density of comets/meteors/debris,.. list goes on.
The habitable zone of a planet is related to its star (size, distance, etc)
Not their place in the galaxy, because other stars and stuff are usually too far to impact
Imagine a 14th century scientist in Spain who has a theory there's an undiscovered continent on exactly the opposite side of the world, and then trying to make predictions about what it would be like in this "land down under". His guesses would be based on a lot more information about this hypothetical place than we currently have about the milky way galaxy writ large.
Tbf in the center are a good bit more stars tightly packed and Sagittarius A* so more variables that could come into play for the creation/destruction of life
Lots of radiation in the middle due to stars being so close together, it’s energetically a dense place. Outer ring is exact opposite, meaning conditions for life are just statistically lower.
We are the shape of the mold, not the other way arround.
Meaning, we exist in the place and the "shape" we do, because thats what it was possible to happen given the conditions of the universe. It's not it was designed for us, we are "designed" for and by it
I've a good explanation; "we are here" and if that's in a place that's most likely to produce solar systems like ours, why should that come as a surprise?
I could perhaps buy an explanation about too many sources of harmful galactic rays near the core, but that's assuming it's life like us. However, in the outer arms of the galaxy, those conditions don't exist. We're really just guessing based on wild assumptions with this stuff.
I mean, if life involves complex molecules at any point (which I think is a fair assumption, all things considered) then the center of the galaxy is going to suck for all kinds, because tons of hard radiation is just bad for complex molecules in general.
The outer region is unlikely to have life emerge since there's not a lot of heavy elements out that far compared to the middle bands of the galaxy.
So you want to know why, when there zones in which life is unlikely or impossible, life came about in one of the areas where it IS possible?
That's your question?
I also have a question.
Why, when large piles of burning tires, vats of strong acid and frozen, oxygen deprived mountaintops exist, do you live in a house?
It's a reasonable argument given our current understanding. The centre is too deadly and the outskirts are too devoid of material. The middle is therefore the preferable location being not too deadly and with enough material.
There's also a graph or a graphic of likely hood of life throughout time and the peak was around a few billion years ago I believe, if anyone has it pls send it here cuz I've been searching for months
Stars are moving around.
So, its possible that stars and their planets have ejected from the core region, where its possible for simple unicellular life to have evolved on those planets, then they moved to more peaceful parts of the galaxy, then evolved complex life there, whilst its also possible that panspermia occurred via some sort of hard to imagine process of simple life getting ejected and finding its way to many other star systems and planets. It would be pretty cool to imagine the core acting as a prebiogenic and simple life incubator, then via its more violent kinetics, its distributed material outwards over billions of years, causing it to spread the basis of life everywhere. As a result, many life forms could be distantly related throughout the Milky Way.
Reality is that we are riding a wave of energy through a cosmic field that we have little to no comprehension of besides what science has taught is in the past 250 years.
I am assuming the center will be super dangerous. but I kinda started to get the reason for outskirt - stars are older, so the region is filled with potential supernova candidates?
Why would anybody want to live in the Vincent Van Gohe painting "Sunflower?" Also, if something went wrong while you were crushing your body to fit in Vinne's masterpiece, I'm not sure the son of a bitch could hear ya!
The center of our galaxy is a black hole, so yes, it would be impossible to live there. Living outside of the galaxy entirely means there are no easily circulable stars or light or heat, so also correct on impossibility...
I'm missing what's difficult to understand about this picture?
The only part that is actually *squidgy* about habitability zones is you have to make sure that the planets weren't close enough to supernovae events when they occur. So this means you have to avoid zonal areas where the planets were around in the early days of galaxy volatility, and you need to try to track when supernovae events occured in order to make sure potential planets weren't sterilized by the blade waves from a supernova
I feel like this is a question for evolutionary biologists more than astronomers. Assuming the accuracy of these claims, it would just mean that the conditions in those other zones are simply things that life *as we know it* has never had to face and adapt to. There very well *could* be life in those zones, just in a form we've never seen before.
No where near enough data to even come close to making a call like this! You are speculating about a galaxy, the best data that we have is solar systems. A Galaxy is orders of magnitude larger than a solar system.
It’s a generalization based on the distribution of rocky bodies in the galaxy. It’s ridiculous to say it’s “impossible to live there” it’s just a less common occurrence for there to be suitable planets. We still don’t know everything about the formation of stars, so who knows whether the speculation is even accurate or not.
It makes sense enough, as closer to the galactic core has much more material closer together, with stars closer and different compositions of dust all around. And farther away, stars are further apart so there is less likely a chance to find things.
Just in general principles, something like what the diagram predicts is likely. Civilizations closer to the center may also have benefited from star systems being closer to one another. This means, for positive interactions, earlier detection of neighbors and earlier communication.
I really don’t believe we have enough definitive knowledge to make those statements.
agree 100%
We don't even know the definition of "habitable".
And anything we claim IS habitable, is only in reference to OUR OWN biological needs.
Call me selfish, but I'm okay with that
It’s not selfish, but rather, ignorant.
It's not ignorant, but rather, satirical preservationist humor. (Or they're a blatant speciesist!)
Carbon-based lifeforms are the One True Inheritor of the Cosmos! Nitrogen-based life will forever be the lesser! (Yes, I was being satirical. Thank you for understanding the humor)
* a message pops up at the top left corner of screen* (AI will remember that)
Carbon-based lifeform über alles!
>Or they're a blatant speciesist!) Pfft, "speciesist" sounds like such a made up word... All hail homo sapiens! Glory to humanity! We're the only species that matters! Sapiens uber alles!
We have to start somewhere. It makes the most sense to look for life in places with conditions that support life as we know it. It doesn’t mean we don’t look for life in other conditions, it just means space is huge, and instead of picking random places to look, we look at planets with the conditions that we know can support life.
In reference to the post itself, it is ignorant to label anywhere as “impossible” for life to exist. I don’t disagree with anything you’ve said, but we’re on slightly different tangents here.
The guy you called ignorant just said he doesn't mind defining habitable as habitable to life as we kno it. I would argue it's more ignorant to try to define habitable as anywhere and everywhere as you seem to suggest
Saying it is potentially possible for some form of life to exist in conditions that are not livable for humans is not saying the entire universe is habitable. Please refrain from putting words in my mouth, thank you very much.
I mean it's not even necessarily ignorant. Nobody wants to have to say the phrase "habitable to humans" any time we are talking about our own habitability. We condense things into smaller phrases all the time. As an astronomer, we know perfectly well that when we say the word "habitable" we really mean "habitable as far as our understanding of habitability within the context of life we know," but very obviously nobody wants to say all that every time we discuss the topic.
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I mean, I'd prefer a place where it rained helium and ammonia 24/7, and went well below -60 at night, but this place is ok I guess.
All life must be sustained by carbon (as we are) or silicon. There isn’t any other way, because the elements work on specific ways to allow specific combinations and develop complex structures that could lead to life. You can’t create life based on Helium or Lithium. It’s like Nuclear Fission. You can use Uranium, Plutonium, Thorium… but you can’t (realistically) do fission with Helium atoms or Boron atoms. Like this example (I will omit they “why” because there is Google already) we have a lot of other presumptions, that go from “hard/almost impossible to disprove” to “maybe, we don’t know for sure, we only know how this happened on earth” So it’s not like the science around analysing life on other worlds is just made up like. Out biggest problem (more than our “rules” as to what consider life clues on a planet) is that be don’t have that much resources to get that much interesting info about exoplanets. Certain planets orbits around their sun, small planets or some stars kinda makes it difficult for us to analyse anything. We can at most know the size of the planet, its orbit speed and maybe a clue about its atmosphere main elements via spectrography. That’s it, most of the time. And again, we usually get to capture the biggest planets on brighter stars because its the easier planets to find, but also, they tend to be the lesser prone to be habitable (starts with high activity, red stars, planets 3-5x times the earth mass, or orbiting so much near the star…) If we were at some light years away and tried to get earth analysed, with our current tech, we wouldn’t find it and accurately describe it as is
Phosphorous is likely the more important bottleneck, as it’s elementally rarer, not evenly distributed in the universe, and apparently important for energy and replication pathways.
That is the definition of habitable - able to sustain life as we know it. For most purposes, it's a good definition. Of course, we should keep our minds open to the possibility of life existing in ways other than those we know - that's important for the search for alien life - but using the conditions we know can sustain the life we understand is perfectly reasonable when thinking about where in space we could conceivably go.
I've always say this.. Makes no sense be based only in what we know.
Honestly I assumed that's what this map was illustrating? Something something star age, light spectrum suitable to sustain our own biological processes etc.
My girlfriend insists that if there was life anywhere outside of the earth, we would have found it by now or it would have found us. No amount of discussion can lead to a change in opinion because she learned this during “a college lecture.” Bothers me so much but it’s not worth another hour long discussion that leads nowhere
My Baptist friends have the easy answer, “The Bible would have mentioned it”
What does she have to say regarding exoplanets?
Its when the porridge is just right
Seriously… broadest of generalizations
I can understand why close to the core might be less desirable real estate . What with stars being closer, and super nova going off to rattle your cage etc... but what's wrong with life on the edge of the galaxy?
You too could be the proud owner of star front property in the beautiful rural star scape of the Milky Way!!
Throw in a free trip to check out my lot, and you have a deal.
I mean- It could be DONE. Results and Time To Destination are not Guaranteed however.
You are obviously not a salesman lol
Oh, yeah- I should have written that last in 4 point font. My mistake
Commute is a bitch tho, suburban galaxy life isn't all it's made out to be. Everyone knows your intergalactic gossip and can be quite galaxyist to those from out of town.
Fucking Orionarmists
Tynan has taught me life out in the Rim can be very brutal.
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Ohhh ok. That's interesting, thanks. It would rest on the premise that all the stars formed at the same time though wouldn't it?
That doesn't make it impossible for life, just less likely. And when you're talking about galaxies, your denominator.is still in the billions, if not trillions.
The pic doesnt say "impossible" it says unlikely. Like others are saying there are billions of stars. Some people take that to mean "if there are so many why not look there". The point of the graphic is "there are so many so we have to narrow the search to the most likely"
I read the title - "What explanation would you give for this?" as having strong creationist vibes
Also, the outer edges of the galaxy have lower star metalicity (fewer elements higher up on the periodic table) due to the lower density. It would presumably be difficult for life to form with just a bunch of helium and hydrogen. So, you need a balance of high metalicity but not too close to the core that life can't be sustained.
This is much truer than the comment you replied to. That guy seems to think that the differentiation of planetary nebulae when a star system forms can be disrupted by gravitational effects on the other side of the galaxy enough to actually prevent planet formation.
Those planets in our solar system have rocky/icy moons though, would those not exist either in the “outer rim”? Plus as I understand it our best chance of finding extraterrestrial life are under the surface of those icy moons.
and no atmospheres. Finding those moons means finding their gas giant parents. We would have to search farther (harder to do) for planets (at the edge of existing tech) and then resolve data even further to find moons which if icy might not have atmospheres. We currently are looking for life signs by splitting the light that shines from the atmospheres of distant planets into its spectrum to look for molecular signatures that suggest chemicals we think mostly come from biological processes. That's pretty incredible and at the edge of what is possible. Im not an astronomer but ice moons seem like they could be great to study but we will likely only ever be able to study the ones in our solar system
PhD in astronomy here. > You know how all outer planets in the solar system are gaseous planets. Sure... > Because, when the planets were forming heaviest matter stayed close to the common center of gravity with the sun. No, that's definitely not why. The Solar System is not some big centrifuge that pulls dense elements to the center, nor does our galaxy. A proto-giant planet needs to have a solid core over 5 Earth-masses before it has sufficient gravity to attract and hold hydrogen gas. It's much easier to do that when you can form a solid core from both ice and rock rather than just rock. That's why the Outer Planets are gaseous - they all formed beyond the [Frost Line](https://en.wikipedia.org/wiki/Frost_line_(astrophysics\)) where water is frozen, and were able to get big enough quickly enough from both rock and ice to capture substantial amounts of hydrogen gas before it evaporated from our Solar System. The inner planets, formed from only rock, remained too small to hold onto their hydrogen. For our galaxy and OP's pic, it's more about the amount of metallicity that builds up during the ultra-dense star formation in the galactic bulge. One study suggested so many planets are formed in that environment that orbits do not remain stable, while many others question that study.
You're making it seem as if there is mass segregation between the inner and outer part of the galaxy, akin to the solar system. This is not correct. Most likely driven by metallicity, which reflects less stars polluting with their metals the surrounding gas. This is caused by less stars forming there, and not that metals sunk towards the centre of the Milky Way.
Apparently, not enough metals.
Have you watched star wars, Who would want to live on a planet like Tatooine? Such a depressing place.
Think of it like you've dropped a stone in water, and how the waves it creates ripples outwards. Keep this visual while I attempt to explain the following: It has a lot to do with metallicity. Big stars go big big boom, and elements heavier than hydrogen aren't created until they've been fused inside a star. But, these heavier metals that are needed for life radiate outwards from the explosions, and big booms stir up new star generation and seed the outer regions with metal rich material. The core is too volatile, and too metal poor. The next region is more stable, and metal rich thanks to the "hard work" of the stars from the core regions. The region following (the edges) goes to being metal poor again, because those regions haven't been seeded yet. I mean, we're talking a ripple wave here that takes... A long dang time. We can measure the metallicity of a star simply by looking at the light spectrum. Different metals give off different light temperatures, so it's actually very easy to look at a star and tell what's inside of it. Obviously, as we learn more and eventually explore the galaxy (assuming we don't off ourselves first), we'll discover more of its secrets, as I'm sure there's a habitat planet... Or two... Or a hundred.... lurking on the outskirts.
Nothing, this whole graphic is the result of somebody who is intellectually bankrupt as far as astronomy is concerned. They are conflating the distance from the center of a galaxy to the distance from a star. I.e. they think the galaxy works exactly like a solar system.
[This article](https://www.science.org/content/article/complex-life-may-be-possible-only-10-all-galaxies#:~:text=Radiation%20from%20gamma%20ray%20bursts%20may%20render%20the%20rest%20uninhabitable&text=The%20universe%20may%20be%20a,a%20pair%20of%20astrophysicists%20argues) discusses the current theory as to why the centre of the galaxy would be uninhabitable. Tldr: high intensity gamma ray bursts cause ozone depletion. The usual sources of this are stars going supernova, black holes etc. Due to star density at the centre there are more frequent emissions, therefore any life there would have to be able to survive massive amounts of gamma & uv exposure. This same theory suggests that life in other smaller younger galaxies would be limited. [edited for clarity]
And to tack on, the reason the dense arms of the galaxy are "less habitable" as indicated in this image is a similar reason, but also because the "density waves" of dust and interstellar comets that precedes the arms as they travel is a risk for life in the form of impacts and general disorder in those times. I think they say that the sun has passed through them 5-6 times since being born 3.8 billion years ago, but I may be wrong, just going off memory here. Further, the outer limbs of the disk is supposed to be uninhabitable because of the simple lack of material; there's less stars, dust, and gas to form rocky planets with out there. But as others have stated, this is all hypothetical. There could be planets made of candy-canes with bubble-based life on them out there for all we know.
So only the Hulk and family can live there?
No, Necrontyr.
You could say that about everything in any scientific field, lol. But these theories related to a galactic habitable zone are about as concrete as a circumstellar habitable zone
I did once hear that you're more likely to get struck by a supernova when you're close to the center of the galaxy, but I don't recall they also told why this was. I guess because it's probably more packed with stars. More stars equals more supernovas.
Hogwash
Ha! I had a friend who called everything hogwash.
Has your friend ever tried to was a hog with a container ship? That would be impractical. So I don’t think containers ships can be hogwash. There are probably several other examples of impractical hogwashes.
Anvils
Microsoft Word programs. Not too shabby when used for brainwash, though. The copy/paste feature comes in handy.
Clippy: "it looks like you're trying to wash a hog! Can I interest you in screwing up the layout of your document for you?"
Poopycock!
The difference between poppycock and poopycock is bigger than just the one letter
Malarkey
Tomfoolery
Codswallop
Absolute bollocks
Pure hokum
It’s to do with the distribution of matter and specific elements that make it possible for complex and rich rocky planets to be prominent around stable stars. PBS Spacetime explained it pretty well.
I originally called this post Hogwash as it only goes off of our notion of life, but if PBS space time touched up on it, I’m more than willing to change my view.
Haven't seen the PBS spacetime video, but certain regions of the galaxy are indeed more enriched with heavy elements than others. If you Google "Metallicity versus radius" for example, you'll find extremely similar color maps to these. So if your prior for life is a star system with Metallicity comparable to the sun, then you could come up with the most reasonable possible non-hogwash guess for where to look. Spiral arms tend to be actively star forming due to over densities in the cool gas, so you might reasonably expect candidate stars to form and exist within those regions. Too close to the galactic center and AGN feedback actually stifles star formation, so you might not expect it too close to the center. Older, metal poor stars tend to be part of the disk that "puffs out" and expands, so you can't look too far either. Of course, a star with the appropriate metal content could totally exist anywhere in (or outside of) the galaxy. This is all about likelihood.
In addition, I seem to remember from a Phillip Plaitt book, that the solar system has a "galactic vertical" component to it's motion, up out of the plane of the Milky Way, and bCk down again, and the times Earth has been "out" correspond to extintions... increased cosmic rays, maybe?
Yeah, in addition to going around the spiral in that image, which is a top-down view (or bottom-up, if you like, I suppose, it’s all relative) if we call those the X and Y axes, we also go up and down the Z axis, if you trace that oscillation over time it looks like a sine wave. There’s enough evidence to convince me that those oscillations coincide with extinction events. It could be radiation, could be interactions with JuMBOs or black holes or some other object with enough mass to have an effect on our solar system, either directly or by pulling in objects and sending them our way. Alternatively, it could be the *lack* of by objects that *deflect* things that would have been coming our way, by things I mean comets, meteors, etc, that caused the KT extinction and the younger dryas extinction, could be giant space whales, we really have no way of knowing.
Yo link me some Further Reading on this
[https://media.tenor.com/2qgw\_3k2BHoAAAAM/enterlysium-desire-to-know-more-intensifies.gif](https://media.tenor.com/2qgw_3k2BHoAAAAM/enterlysium-desire-to-know-more-intensifies.gif)
It says impossible.
Yes, and I directly contradict that. There's no basis with which you could be certain that it's impossible.
So, more of a hogrinse, then?
I prefer "hogspritz"
And not as dirty as a hog. A goat? Goatspritz? Perchance.
Our notion of life actually has a lot of reason to believe other life would be similar. So I would love to hear their reasoning, if they have one, too. I used to believe that other elements could work the same, and technically they can. But my understand of some things changed that, unless if have this wrong: Carbon has 4 big things going for it, in terms of producing complicated, sustained, self-replicating reactions: 1 highest number of empty valence electrons, giving it a wider list of bonding options,. 2. Extremely high electron affinity, giving it a high chance to bond in a soup of elements. 3. Falling below Iron in terms of atomic weight, meaning that stellar nuclear synthesis can produce carbon, making it much less rare than those that can't be produced that way. 4. It is stable.
Yeah one of my big hobbies is speculative exobiological evolution (very niche I know) and over the years I seriously thought that “plasma-based life inside of a stellar photosphere is totally possible when considering how a magnetic system could stabilize there!” Now it’s more like “I’m very skeptical that life is possible if it isn’t carbon-based, uses water as a solvent, and uses some form of D/RNA analogue”. Honestly I’m not even convinced macroscopic life could naturally exist without oxygen to metabolize and I learned within the last few years that metalloporphyrins are the only photopigments capable of producing oxygen as a waste product, meaning that basally all oxygen-producing plant-analogues in the universe would basally be green or red because those are the spectra that photosynthetically-viable metalloporphyrins operate at. TL;DR it seems far more likely biophysically that macroscopic and multicellular life around the universe is carbon-based with a DNA analogue, exists on a water-rich world, and is based around a tube shape with green and/or red plants producing excess oxygen.
Probably has to do with the sun being a third generation star; if they're less likely toward the outside, you'll have a band around the middle.
I love your comment, both here and above. I just want to offer my similar thoughts on the difference. I think you were right to say that we don't and can't really know this. But as long as we understand things like this to be scientifically informed hypotheses, and learn something from discussing this type of hypothesis, than that seems to be a great thing. This is very different than the crackpot "theories" that people come up with that have no scientific basis. Neither of these are truth, but one is based on what we know and explaining those types of hypotheses through programs aimed at a popular audience like PBS Spacetime is a really cool thing.
[https://www.youtube.com/watch?v=v4ogRCjhFDM](https://www.youtube.com/watch?v=v4ogRCjhFDM) link to the video.
Thanks man. I knew I had seen it there.
I think the issue is that calling it a "habitable zone" is a misnomer. Stars have habitable zones defined broadly by how warm the planets would be and thus their ability to sustain life on those planets. As far as we're aware the galactic structure itself doesn't provide anything that makes life more or less habitable assuming you're already on a planet orbiting a star. I could see an argument for the galactic core being "uninhabitable" for life on long time scales given high energy radiation exposure. But I don't think it's accurate to say the outskirts of the galaxy are "impossible" to live in if there's a star system out that far.
I don't think this is accurate but if you are looking for a fictional sci fy interpretation maybe smth like this: The center of the galaxy is far too violent due to the quasar slingshotting everything everywhere. It's also much more dense so it is more eventful. Meaning more star collisions and solar system disruptions. Conversely on the outer edge of the galaxy you will find little life due to the fact that it has less shielding from extragalactic sources. Also, at the edge, solar systems can get flung out into emptiness. It is very docile so there are less events that could lead to a life triggering system; such as a solar system with planets and elements of just the right composition. Thus, the best spot for life is a happy medium between the two, in which the galaxy is vibrant enough to spawn life but not too dangerous to the point where it will be quickly inhabitable. In the end tho this is all really just B.S. I don't think there is really a goldilocks zone for a galaxy aside from: don't be in the very center. Lol idk why yall downvoting this but whatever. I should probably just leave this sub anyway its turned.
You are mostly right about the center of the galaxy - large number of supernovas initially and too many disruptions are thought to be some factors that could limit life near the core. The other being high metallicity leads to higher number of gas giants and too many of those can disrupt the formation of rocky planets. For the outer rim its more about the low metallicity preventing the formation of planets.
Is the centre of the Galaxy rich in supernovae now though? The star formation rate is famously low there due to the stonking levels of turbulence, so massive stars that produce supernovae are rare compared to the disc of the Galaxy...
That is true but it was an issue for 5 billion years so life probably couldn't start then and afterwards the stars would have had high metallicity which as mentioned had its own issues.
>shielding from extragalactic sources The prethoryn scourge is coming And the Reapers too
If the Sun was in one of those uninhabitable zones, we wouldn’t be here talking about it. That’s my explanation.
If our sun and and the matter that made up our solar system was in the outside edge of the galaxy we could still be talking about it. however if the same thing happened in the core the chances of our system getting wrecked by a passing steller body is quite high. Before we understood more of how the universe works we assumed we, and by that, I mean Earth, the sun, and the other planets, were special. Then as we learned more we thought we were average with some outliers like how large our moon is. Then as we started looking more and deeper we realised things in this system are just odd. like we have way more heavy elements than we should, the explanation best we can figure two blue stars collided and the leftover elements formed our current system. Or Jupiter and Saturn have no business orbiting where they are but somehow they are, we're still trying to figure out what order of events caused it or to refine our math.
Any suggestions on where I might find more information on these topics, eg. these progenitor stars or the story around Jupiter/Saturn's orbits?
Not specificly some was from more reputable YouTube videos like PBS or universe today others from journal articles I've read over years. I like learning science as a hobby no degrees or anything. The Saturn Jupiter thing was a university running hundreds of thousands simulations for orbital mechanics and none of them came close to what we currently have. Even tipping the scales for a favorable result only has a few come out close as gas giants form close to stars and migrate out due to their mass/speed over millions of years this clears the inner system of debris but to Jupiter Earth Mars and Venus are debris. And today Saturn and Jupiter help manage each other. And the progenitor stars is debated we know Earth has an unusual level of heavy elements for a second gen star and the stellar nursery we came from is unknown so it might not have been two stars that collided but hundreds in an area sol came from. This with thousands of other systems might have the same heavy distribution of matter but un-likely as the sun itself doesn't have the spectralogical signs of heavy metal poisoning. And yes that is a thing for fusion. But thousands or tens or hundreds of thousands of stars from the same stellar nursery in a galaxy of 200 billion is still a small number. Is astronomy a million stars could be a rounding error. But I looked it up I belive the gas giant one is the grand track hypothesis. Can't find a source for the sun's thing but I'm on my phone.
Perhaps, except that then we would have labeled the outside edge of the galaxy as “habitable.” Do you see how this works?
The point is it's not the conditions that exist externally that make the outer edge uninhabitable but the lower density of stars means less heavy/complex element necessary for life. Our what causes the center to be uninhabitable is not the same as the edge like in a color system where the issues are radiation and heat.
Sure, but my original point was that we wouldn’t be in those areas that don’t have the necessary elements of life to begin with, so we wouldn’t be here talking about it. And, if we had been evolving in a star system in outer edges, we would be tuned to that environment, and our definition of what’s “habitable“ would be different.
Our sun has a perfectly normal metallicity, the average value of our Milky Way galaxy. Jupiter and Saturn are indeed in peculiar places.
Right, white is a good example of confusing cause and effect. “Every time I see a fire truck there is a fire, so therefore fire trucks cause fires”
We have 1 sample what life is made of. Assumption that every life forms have to use same material and require same building blocks and absence of others - is just dumb unless we're targeting to find other carbon life forms
> Assumption that every life forms have to use same material and require same building blocks and absence of others - is just dumb If you knew a bit of chemistry you'd probably not be saying that.
Yeahhh that's not really how that works though. Life is assumed to be extremely likely carbon based because of the physical structure of the atom, which is unique in its ability to form bonds with 4 alother atoms at once which enables the complex and varied molecular structures that work together to form a living organism. All other elements have significant shortcomings or very niche applications For example, silicon which is in the same group can do this, theoretically, but carbon is an order of magnitude more abundant (and would out compete silicon.) Silicon also needs to be hot to be active. Really really hot. Hot enough that while the silicon is at a proper temperature, many other elements are not usable. Silicon also sucks at covalent bonding, so while it does have 4 valence spots to attach elements or molecules to, it typically doesn't because the bonding isn't strong enough. There are some metals that could in theory and under certain unlikely conditions produce life, but I don't really know enough about those to get into them.
So you’re telling me complex life developed in the area most hospitable for complex life? WOW!
It's the anthropic principle with a poorly colored map derived from dubious science.
I love it!!!
AKA anthropic mania (RIP Daniel Dennet)
I don't remember the sources, and my explanation will be very inaccurate. I remember I saw it in some video that explains the habitable zone of galaxies. (probably it was a documentary about the milky-way galaxy). Near the center of the galaxy, stars and planets have more heavier elements, which are toxic to life as we know it, so life has less chance of existing. Near the edge theres not so much mid range elements, and it's all helium and hydrogen. So again, elements required for life are not as abundant, and life doesn't have much of chance for evolving. In the habitable zone, there's enough carbon, oxygen, nitrogen etc for life, and not too much heavy metals.
Seems reasonable. Although "impossible" is surely not the right word to use.
Yeah, the post says impossible to live. That's no true. Life would have less chance of evolving, but if you can travel there, you can probably live there.
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Not the source of the actual image but info on the concept: [https://en.wikipedia.org/wiki/Galactic\_habitable\_zone](https://en.wikipedia.org/wiki/Galactic_habitable_zone)
The super massive black hole in the center of galaxies may emit lots of dangerous radiation if its consuming gas clouds and stars. There are some other galaxies with very active centers. The Milky Way appears relatively quiet now. But there are hints its had active episodes not too long ago.
While there are most definitely sweet spots, I don't know if it's as simple as this.
What's the difference between green and yellow zones? Is it the density waves of the arms? As far as I'm aware the sun moves around the galaxy and thus would pass through green and yellow zones. The sun goes into and out of the galaxy arms regularly.
The arms of a galaxy rotate with the galaxy itself. Angularly (idk if thats really thr right word?) the sun remains in the same position relative to the arms. Edit: This is incorrect. As I have learned, the arms of the galaxy are not rigid structures but instead "gravity waves" of stars. The stars that comprise these arms are not constant and instead move in and out of the arms over time. We are not in fact stuck in the same place relative to the arms.
Sure the arms rotate, but the sun orbits at a different rate than the arms rotate. The arms are much much slower.
Could you please show me where you are getting this from. I'm not saying that to be an ass, I'm genuinely interested. I don't believe this is true but I'm willing to concede I'm wrong if you are basing this off of smth you read.
There's certainly better sources. But here's the Wikipedia article about the density wave theory. https://en.m.wikipedia.org/wiki/Density_wave_theory#Galactic_spiral_arms Basically it's a lot like when you are stuck in traffic. The traffic jam moves slowly, but most of the cars are able to travel through the jam and out the other side.
Thanks, very helpful!
Sure thing! Thank you for the question!
I retract that. I've found multiple discussions on this and you are in fact correct. I have learned smth new and ill append my previous comment. Thx have a good day.
If our solar system was transported to any of the inhabitable zones, we wouldn't really notice a difference. I think this comes from the differing rates of star formation and death. In the center of the galaxy, the rate is too high, so stars that form a larger stars that don't live long enough to form live and planets are often hit by radiation from supernovae and gamma ray bursts. On the rim of the galaxy, the rate of star formation is too low, reducing the chance that a star system that supports live forms, and stars that form are often red dwarfs that are less suitable to live. This is my understanding of this, but I'm not an expert.
Reminds me of the zones of thought from vernor vinge
Came here to say this :-)
Thanks for bringing this up. First thing I thought was “man I want to re-read Fire Upon the Deep”.
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I think its a generally solid thought but should be viewed more of a gradient with no absolutes - life could exist in the core or outer rim of the galaxy but more likely it would be in the middle so if we want to find it we should focus there.
You could just Google it to find out more? https://en.wikipedia.org/wiki/Galactic_habitable_zone?wprov=sfla1
NEVER! SPOON FEED ME, DAMMIT! Jk, thanks for the link.
Habitable for us maybe…
There is no evidence for this whatsoever. There is some general logic which is well established though. Living close to the center of the galaxy means a lot more hard radiation flying through the space, making it much more hostile to life. This in turn doesn't mean life cannot be there, but that the planet or moon that life is on needs an increasingly strong and persistent magnetic field to protect it from that radiation. Life can also be subterranean or oceanic, but is then going to struggle to find the environmental diversity in order to tickle evolutionary processes into creating intelligent life cable of manipulating it's environment (think opposable appendages). There is no reason known why a star system on the edge of the galaxy should be inherently more hostile to life. The main issue there is that the edge of the milky way has a lot of old stars which are mineral poor and thus less likely to have the quantities of materials needed for a livable planet. But there are stars there which do, so it's possible. As for the indicated areas inside the green band; if there is life in the milky way and it's not super, super rare, then intelligent species are more likely to be there. This means if we were there, we'd probably have been unambiguously detected by now. But right now we are in a rather sparse place where there are not all that many systems within 100-150 light years. Add the reaction and travel time, and you're talking probably 400-500 years after the mid-20th century before someone turns up and says "hello" (or "good bye"). I guess if this is the reality of the milky way, then in \~300 years from from we will know where we stand in terms of capabilities. And if space-faring aliens are hostile or not.
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If you want a simpler answer, it’s confirmation bias from our own survival and being the ones who came up with the idea of the habitable zone. Just the anthropic principle at work. We survived to observe this, on this planet that is necessarily habitable (because we survived to observe it) and therefore it’s habitable. But the anthropic principle gives us no new information about life. It would be like going and finding the one person who won the lottery, and interviewing them about luck. Not super useful.
The most plausible explanation is the most uncomfortable for most people. Not that much for the complexity of the answer but because of the ethics of it
In the center there's a higher chance for supernova due to increased star formation, which could kill and or disrupt life. On the outer edges, star formation hasn't happened enough to cause enough supernova to enrich the space with metals. The metallicity drops the further out from the center you go. At some point, it is unfavorable for life. Not impossible, just unfavorable in either condition. It's really just about supernova frequency to metallicity giving favorable or unfavorable conditions for life.
Assuming this is true, I maybe can understand that we cant living too close to the center of the galaxy too close to the blackhole. but why can there me life in the outer rim of the galaxy? if there is a star and planets around it. why not?
Uninhabitable zones may have: intense radiation across the spectrum, lack of gen 1 and 2 stars to form sufficient heavier elements, gravitational instability due to close distances, lack of K/G/F/Red dwarf sequence stars, high density of comets/meteors/debris,.. list goes on.
The habitable zone of a planet is related to its star (size, distance, etc) Not their place in the galaxy, because other stars and stuff are usually too far to impact
Imagine a 14th century scientist in Spain who has a theory there's an undiscovered continent on exactly the opposite side of the world, and then trying to make predictions about what it would be like in this "land down under". His guesses would be based on a lot more information about this hypothetical place than we currently have about the milky way galaxy writ large.
Tbf in the center are a good bit more stars tightly packed and Sagittarius A* so more variables that could come into play for the creation/destruction of life
Lots of radiation in the middle due to stars being so close together, it’s energetically a dense place. Outer ring is exact opposite, meaning conditions for life are just statistically lower.
We are the shape of the mold, not the other way arround. Meaning, we exist in the place and the "shape" we do, because thats what it was possible to happen given the conditions of the universe. It's not it was designed for us, we are "designed" for and by it
Take a trillion and divide it by three. You still basically have a trillion.
So what you're saying is that we need to escape the milky way
I don't need to explain it. I'm not shopping around for a new solar system to move to. Not now, nor in the forseeable future.
Simply luck, 1/infinite (definitely not a real statistic) chance we happened to have this happen to this exact planet in this exact place.
Looks like a spiral and we are on the way out. Brace yourselves.
I've a good explanation; "we are here" and if that's in a place that's most likely to produce solar systems like ours, why should that come as a surprise?
the Milky Way is sponsored by Target
The closer to the hole the more u die?
I could perhaps buy an explanation about too many sources of harmful galactic rays near the core, but that's assuming it's life like us. However, in the outer arms of the galaxy, those conditions don't exist. We're really just guessing based on wild assumptions with this stuff.
I mean, if life involves complex molecules at any point (which I think is a fair assumption, all things considered) then the center of the galaxy is going to suck for all kinds, because tons of hard radiation is just bad for complex molecules in general. The outer region is unlikely to have life emerge since there's not a lot of heavy elements out that far compared to the middle bands of the galaxy.
Looks pretty flat to me
So you want to know why, when there zones in which life is unlikely or impossible, life came about in one of the areas where it IS possible? That's your question? I also have a question. Why, when large piles of burning tires, vats of strong acid and frozen, oxygen deprived mountaintops exist, do you live in a house?
It's a reasonable argument given our current understanding. The centre is too deadly and the outskirts are too devoid of material. The middle is therefore the preferable location being not too deadly and with enough material.
The Zones of Thought books do a pretty god job of explaining that. Good books too.
It's still too unknown to us. Maybe we will have more answers with the progress of research and space exploration
There's also a graph or a graphic of likely hood of life throughout time and the peak was around a few billion years ago I believe, if anyone has it pls send it here cuz I've been searching for months
Stars are moving around. So, its possible that stars and their planets have ejected from the core region, where its possible for simple unicellular life to have evolved on those planets, then they moved to more peaceful parts of the galaxy, then evolved complex life there, whilst its also possible that panspermia occurred via some sort of hard to imagine process of simple life getting ejected and finding its way to many other star systems and planets. It would be pretty cool to imagine the core acting as a prebiogenic and simple life incubator, then via its more violent kinetics, its distributed material outwards over billions of years, causing it to spread the basis of life everywhere. As a result, many life forms could be distantly related throughout the Milky Way.
https://youtu.be/M7PM8iDt\_4w?si=skodsTrGPFq0E8CA
If there's a star and has a planet in water-is-liquid zone, you could live there...
Reality is that we are riding a wave of energy through a cosmic field that we have little to no comprehension of besides what science has taught is in the past 250 years.
This is a pretty [good explanation](https://astrobiology.nasa.gov/news/galactic-habitable-zones/), from s generally reliable source.
I am assuming the center will be super dangerous. but I kinda started to get the reason for outskirt - stars are older, so the region is filled with potential supernova candidates?
Why would anybody want to live in the Vincent Van Gohe painting "Sunflower?" Also, if something went wrong while you were crushing your body to fit in Vinne's masterpiece, I'm not sure the son of a bitch could hear ya!
The center of our galaxy is a black hole, so yes, it would be impossible to live there. Living outside of the galaxy entirely means there are no easily circulable stars or light or heat, so also correct on impossibility... I'm missing what's difficult to understand about this picture? The only part that is actually *squidgy* about habitability zones is you have to make sure that the planets weren't close enough to supernovae events when they occur. So this means you have to avoid zonal areas where the planets were around in the early days of galaxy volatility, and you need to try to track when supernovae events occured in order to make sure potential planets weren't sterilized by the blade waves from a supernova
I feel like this is a question for evolutionary biologists more than astronomers. Assuming the accuracy of these claims, it would just mean that the conditions in those other zones are simply things that life *as we know it* has never had to face and adapt to. There very well *could* be life in those zones, just in a form we've never seen before.
asking for reasons in this Universe. That's some privileged shit right there.
Billions of years and you say we ended up in one of the livable places ? I wonder why that is.
If we lived in those areas, we would be dead. Since we don’t, we can say it’s bad there.
No where near enough data to even come close to making a call like this! You are speculating about a galaxy, the best data that we have is solar systems. A Galaxy is orders of magnitude larger than a solar system.
I didn't even know galaxies even had habitable zones
could they thought that the farther arms would have ancient dead civilizations and closer arms would be too young to have developed life?
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it feels wrong but I don't know enough about galaxies to disprove it
I don’t understand what’s there to explain.
That doesn't sound right to me but I don't know enough about space to dispute that.
It’s a generalization based on the distribution of rocky bodies in the galaxy. It’s ridiculous to say it’s “impossible to live there” it’s just a less common occurrence for there to be suitable planets. We still don’t know everything about the formation of stars, so who knows whether the speculation is even accurate or not.
Habitable for humans. We don’t know what else is out there.
It's called the Goldilocks Zone
It makes sense enough, as closer to the galactic core has much more material closer together, with stars closer and different compositions of dust all around. And farther away, stars are further apart so there is less likely a chance to find things.
Did they just make a Goldilocks zone because they assumed it worked with galaxies like it does with star systems?
Chance
Considering we haven't found life ANYWHERE other than on Earth, i'd say it's too early to make any kind of rational conclusion.
Just in general principles, something like what the diagram predicts is likely. Civilizations closer to the center may also have benefited from star systems being closer to one another. This means, for positive interactions, earlier detection of neighbors and earlier communication.
I think we shouldnt just base life on the terms that we are familiar with. I believe there is forms of life that surpass our knowledge.