A simple question; How many known galaxies have the possibility of supporting human life?
All of them, unless I am severly mistaken.
Right Astroboy. No eaxct # of galaxies is known, becuase there are so many, here is the scale tho Moira:
Number of large galaxies within 15 billion light years = 10 billion
Number of dwarf galaxies within 15 billion light years = 100 billion
We can barely determine if nearby solar systems within our own galaxy have terrestrial planets, much less if those can support life.
Galaxies are too far away to determine if their constituent stars have habitable planets. But if we ever determine that our “local” stars can or do, then we can probably assume that similar galaxies to our own have life-supporting planets. (I think we have to have proof that our little blue planet is not a unique freak occurance.)
Agreed, AWB, but the question was regarding the POSSIBILITY of human life…
Antartica is pretty human-type life unfriendly, but people live there for research purposes. Other possible places in this (let alone other) galaxies seem to be numerous… IE: several planetary systems have been detected nearby… by deduction, we can infer that MANY others exist as well… in this galaxy as well as others.
However, the gap between “may” exist and “do” exist is a large one…
Then let me refine my question. Of the “known” galaxies, which have the capability of supporting human life?
I don’t know if you understand what a galaxy is - I is a collection of billions of stars around what appears to be a very big black hole. The stars that we found planets around are within our own galaxy. the distance is so great from one end of our galaxy the the other but that distance is dwarfed by the distance between galaxys.
Becasue of this great distance we have great difficulty studying stars them and know very little about them.
Of the known galaxies, it’s a pretty safe bet that only the galaxies that are relatively close by and have gone through at least one cycle in stellar evolution are the ones that can support life. The very FIRST galaxies that were created had very low metalicity (metal to an astronomer being anything heavier than helium) because no supernovae had yet gone off. Until that happened (after a few hundred million years ago) and the supernovae had released rich material that had a chance to mingle with ISM for a bit (few billion years), there was no chance for lifeforms based on anything more than helium or hydrogen to really develop.
We happen to live in a second or third generation solar system that has a relatively high metalicity, allowing for the carbon, oxygen, nitrogen, and other heavy elements important for life to occur.
Hmm, might a few be knocked out of the running for having over active cores (with or without black holes) which would flood the galaxy with radiation and prevent evolution from taking the easy paths it took to get to us?
Osiris, flooding the galaxy with radiation isn’t so much a problem since as you get farther away from the nucleus, you have less radiation, usually by more than 1/r^2 you’d guess since there is intervening material for absorption. But blowing the metals and the ISM material out is a cause for concern. The low metalicity galaxies at the center of clusters, for example, only have old stars because (as current theory goes) all the supernova material gets kicked out of the galaxy before it gets a chance to form newer stars. If there are no new star formations, there’s no chance for life to take hold… especially if all of your stars have low metalicity to begin with due to being created so early. In short, metalicity is probably a more important factor than active nuclei, though there are some cross-correlations between the two phenomena.
JS Princeton
Insofar as we are not the center of the universe or anything, why do you doubt that galaxies way the hell and gone dozen billion light years away from us that have also gone through at least one cycle in stellar evolution would have any less likelihood of sustaining life?
JS, while I understand what you are saying and partly agree you should understand that I’m adding another talking point and am specifically talking about galaxies way out at the end of the spectrum. Galaxies with hyper active cores.
So let’s say our galaxy has poisonous radiation out to say X light years. And let’s make the absoprtion rate 1/(r^3), very generous I think and of course in real life different parts of the spectrum experience different rates of absorption. So another galaxy with a core 1,000 times more active then ours would be poisonous out to 10X. Now, I believe they can get even more active. So a certain small majority could indeed be flooed with radiation making human life impossible, even with lots of mild suns and warm rocky planets.
I’d also like to add that for a distant galaxy to support human life, we’d have to physically go there, as the odds of evolutionary processes producing human beings elsewhere on the timescale of the current age of the universe are infinitesimal.
Excellent question. When I talk about a given galaxy, I’m talking about a given observed galaxy. This is the only thing astronomers can really talk about because, well, because that’s all we can see. I know what the nearby (in time AND space) galaxies look like and I can see the galaxies far away (in space and BACK in time) are different. I can therefore say, with some assurance, that there will not be life in these metal-poor galaxies that I OBSERVE.
Now, since the time indicated by our observations, these galaxies have gone through all sorts of changes (I surmise, by drawing their worldlines). Of course, I won’t know about them for ages to come, and so speculation about what is happening elsewhere (that is outside of our past light cone) is really just that. However, if you want, you can say that galactic evolution has gone on and these distant galaxies may very well have high enough metallicity in messages that leave from “those galaxies” (they really aren’t the same galaxies, now) “TODAY” (granting the problem of simultaneity of worldlines) we may see evidence that life could exist in a few billion years. This is discounting the fact that galaxies over that period of time tend to change, merge, fall into structures, get spit out, and generally are NOT the same galaxies at all. It’s the old story of my great grandfather’s old axe. You’ve heard it, “In the cellar, we’ve got my great grandfather’s old axe. It’s had four new heads and three new handles, but it’s still my great grandfather’s old axe.” This is the problem with talking about the way things are “today” even though we don’t observe them.
Thanks for bringing this point up, it is often lost when astronomers talk to the public. When we say that a galaxy is “12 billion light years away” we aren’t saying that great-grandfather’s galaxy is 12 billion light years away today. Oh no! We are saying that the galaxy we observe that’s 12 billion year-old photons came from a position that is 12 billion light years away from us. As to where “that” galaxy is “now”, we really cannot say (and haven’t the foggiest clue as we haven’t observed it!).
In order to aviod such erudite confusion, astronomers talk about the way things were as that is the observable universe.
Clear as mud?
Osiris It seems to me (though my background in AGN astronomy is weak) that all of the AGNs you are talking about are contained in low-metalicity galaxies to begin with, which makes our discussion even more peculiar. I don’t have the numbers on hand as to how damaging this radiation can be for potential life. It might make for a nice little side-bit of research, though. As I think of it, I seem to remember reading about some school of thought that said in all galactic nuclei there could be no life because of radiation. We may have to explore this issue a bit further.
Geneseric your last comment all depends on what type of speculation you by into. Some believe that the intelligence variable in the Drake equation is very nearly one. (That is, if life can be supported, it will necessarily lead to intelligence). Others believe that is very low, thus explaining the Great Silence (in other words, life may be ubiquitous, but it never becomes intelligent, thus there are no chances for life to develop communication abilities since it is never smart enough to begin with). Who knows which take is right?
Now I’m not saying that “humanity” per se is the only means for life to gain intelligence, but we just don’t know at this point. SciFi writers thrill at conjecturing about such things. To this end, it’s best to say, “we don’t know” and leave it at that, because we really don’t. As far as what it takes to support human life, this is really an up-in-the-air type question. After all, human life was found to be on the moon at one point… a very unlikely place for humanity to find itself, I’d say 
Excellent question. When I talk about a given galaxy, I’m talking about a given observed galaxy. This is the only thing astronomers can really talk about because, well, because that’s all we can see. I know what the nearby (in time AND space) galaxies look like and I can see the galaxies far away (in space and BACK in time) are different. I can therefore say, with some assurance, that there will not be life in these metal-poor galaxies that I OBSERVE.
Now, since the time indicated by our observations, these galaxies have gone through all sorts of changes (I surmise, by drawing their worldlines). Of course, I won’t know about them for ages to come, and so speculation about what is happening elsewhere (that is outside of our past light cone) is really just that. However, if you want, you can say that galactic evolution has gone on and these distant galaxies may very well have high enough metallicity in messages that leave from “those galaxies” (they really aren’t the same galaxies, now) “TODAY” (granting the problem of simultaneity of worldlines) we may see evidence that life could exist in a few billion years. This is discounting the fact that galaxies over that period of time tend to change, merge, fall into structures, get spit out, and generally are NOT the same galaxies at all. It’s the old story of my great grandfather’s old axe. You’ve heard it, “In the cellar, we’ve got my great grandfather’s old axe. It’s had four new heads and three new handles, but it’s still my great grandfather’s old axe.” This is the problem with talking about the way things are “today” even though we don’t observe them.
Thanks for bringing this point up, it is often lost when astronomers talk to the public. When we say that a galaxy is “12 billion light years away” we aren’t saying that great-grandfather’s galaxy is 12 billion light years away today. Oh no! We are saying that the galaxy we observe that’s 12 billion year-old photons came from a position that is 12 billion light years away from us. As to where “that” galaxy is “now”, we really cannot say (and haven’t the foggiest clue as we haven’t observed it!).
In order to aviod such erudite confusion, astronomers talk about the way things were as that is the observable universe.
Clear as mud?
Osiris It seems to me (though my background in AGN astronomy is weak) that all of the AGNs you are talking about are contained in low-metalicity galaxies to begin with, which makes our discussion even more peculiar. I don’t have the numbers on hand as to how damaging this radiation can be for potential life. It might make for a nice little side-bit of research, though. As I think of it, I seem to remember reading about some school of thought that said in all galactic nuclei there could be no life because of radiation. We may have to explore this issue a bit further.
Geneseric your last comment all depends on what type of speculation you by into. Some believe that the intelligence variable in the Drake equation is very nearly one. (That is, if life can be supported, it will necessarily lead to intelligence). Others believe that is very low, thus explaining the Great Silence (in other words, life may be ubiquitous, but it never becomes intelligent, thus there are no chances for life to develop communication abilities since it is never smart enough to begin with). Who knows which take is right?
Now I’m not saying that “humanity” per se is the only means for life to gain intelligence, but we just don’t know at this point. SciFi writers thrill at conjecturing about such things. To this end, it’s best to say, “we don’t know” and leave it at that, because we really don’t. As far as what it takes to support human life, this is really an up-in-the-air type question. After all, human life was found to be on the moon at one point… a very unlikely place for humanity to find itself, I’d say
JS, I’m just saying that whatever intelligent life forms are out there, the random factors and specific circumstances which led to the evolution of the particular intelligent life forms which we call “human beings” are unlikely in the extreme to have happened in an identical manner anywhere else in the universe. Thus, the intelligent life forms which inhabit planets orbiting other stars in other galaxies, should they exist, are almost definitely not human.
It seems to me, although we can’t be certain of several factors in the Drake equation, that any reasonable estimate of the probability of life elsewhere in the universe inevitably leads to the conclusion that such life almost certainly exists. Nevertheless, the odds that “they” are exactly like “us”, must be very small to the point of negligibility.
Not necessarily. The things that really matters is how much matter is pouring into the core. Certainly way back when the universe was new there was a lot more scattered matter to pour in but there are still some large clouds of hydrogen that have yet to be consumed which can really kick up the activity in any galactic core. It’s a small number of galaxies effected but certainly not one we’d wish to ignore.
But “they” don’t need to be “exactly” like us in order for human life to be supportable.
For example, we could ask the question how many places in the solar system is human life supportable? Right now, the answer is one, or is it two? Terraforming of Mars leaves open the door that human life could one day happily settle in on that planet. Does that mean that human life is “supportable” there? All depends on what you mean by “supportable”.
Granted to require EXACTLY the same conditions (radiative transfer, chemical abundances, ecosystem, various equilibria, etc.) that exist on Earth in another place makes the probability low, but there’s nothing that says we have to have exactly the same conditions. We just need to be able to “support” human life. With proper technology, that can be done in very unpleasant environments. (Note: techonology in this case ranges from clothing to oxygen mining.)
True, JS, my point was only tangentially related to the question. Obviously any world relatively similar to the earth within certain parameters would be capable of supporting human beings without life support equipment. Perhaps I should rephrase my earlier post to add in a word I intended to be implied, in order to remove some ambiguity from the point I meant to make…
Maybe I read too much into the OP, but I took it to be asking if it is possible for other galaxies to have humans in them. I see the poster clarified her point in her second post by adding the word “capability” which does change the question somewhat. Nevertheless, until we develop some seriously funky technology (near-light-speed travel, or suspended animation, or worm-hole manipulators, or multi-generational starships, etc.), we can be fairly sure that no other galaxies have actual human life.
Wait, wait, wait… did you mean to say “after a few hundred million years” or “a few hundred million years ago”? Because I’m pretty sure that our system is older than a few hundred million years…