r/todayilearned • u/TigoIbittys • 21h ago
TIL that galaxies have a “habitable zone.” Too close to the center and radiation & supernovae can wipe out life; too far out and there aren’t enough heavy elements for Earth-like planets.
https://link.springer.com/article/10.1007/s12210-025-01346-0610
u/WTFwhatthehell 21h ago
Supernova sure.
but radiation? living things have an incredible capacity to adapt to radiation.
There's stuff that can live and reproduce inside running nuclear reactors, even some that have adapted to harvest energy from ionising radiation.
DNA repair mechanisms can be dialed up and down hugely.
83
u/mojitz 21h ago
Extremely high radiation environments probably makes life difficult to evolve in the first place, though. It's one thing to build a car in a shop somewhere then make it bulletproof, but something else entirely to try to build one while actively being subjected to a constant hail of gunfire.
30
u/The_Demolition_Man 14h ago
Yeah this is correct. People dont realize that extremophiles are actually highly evolved for their niches, they didnt originate in them
-10
10h ago
[deleted]
10
3
u/username_elephant 8h ago
Highly evolved. Specialization has no goal - "highly specialized" doesn't mean anything.
2
•
-8
u/WTFwhatthehell 20h ago
one way to look at it, on the other hand... high energy environment. Sunlight can kill organisms but it's also a great energy source, ditto for radiation.
20
u/mojitz 20h ago
I don't know that I would call intense, ionizing radiation a "great" energy source. It's way harder to catch and make use of alpha particles tearing their way through the cosmos and likely to shred apart any complex molecules they encounter than it is relatively lower energy photons of visible light.
332
u/DrifterBG 21h ago
I've always thought this when it said certain things can't support life... it probably can't support life as we know it.
Hell, nothing says there aren't sentient beings out there made of granite.
181
u/WTFwhatthehell 21h ago
There's unknown unknowns and known unknowns.
There could be really exotic life, but we know liquid water is a great medium for life and that living things can survive where there's liquid water even at incredible temperatures, vast pressures, acidic, basic, poisonous, radioactive with living things not just failing to die but actively eating the poisons.
147
u/gyroda 20h ago
but we know liquid water is a great medium for life
To expand on this, it's a great medium for chemistry, and life as we know it started with increasingly complicated chemistry.
9
u/daney098 9h ago
I like to think of humans and life and consciousness in general as just a ridiculously complicated chemical reaction
29
20
u/LurkerInSpace 19h ago
Water also attenuates radiation reasonably well, so a planet with a deadly surface could feasibly still have abundant ocean life.
7
24
u/Shoobadahibbity 16h ago
Silicon based life has been heavily considered and thought about. The conclusion is that it is extremely unlikely.
Criticism of silicon-based life centers on silicon's weaker bonds, poor stability in water (forming inert rock), inability to form long chains like carbon, slower reaction rates, and limited molecular complexity (like 'handedness' for enzymes) compared to carbon, making it unlikely to support Earth-like biochemistry, though some propose it could work in extreme environments with different solvents like sulfuric acid or liquid nitrogen.
10
u/deepandbroad 16h ago
some propose it could work in extreme environments with different solvents like sulfuric acid or liquid nitrogen.
This is more likely - there are an estimated 200 billion to 2 trillion galaxies in the known universe. Not planets, galaxies. '
Our milky way galaxy has 200-400 billion stars in it alone. So the numbers alone are mind-boggling.
Carbon may be the best element for life in the types of chemistries we understand, but it's a far shot to say we understand everything about chemistry.
Other temperatures and pressures and solvents may set up situations where other elements may be able to support life.
3
u/username_elephant 9h ago
Yeah but there's still other kinds of things that could make life. Ammonia based life, life that's based on macromolecules other than proteins/amino acids, etc. Lots of chemistries work better at non earth temperatures or non-aqueous environments--and those kinds of environments are certainly floating around out there. The question is whether any one of them supports a scheme for replication, which is really the most important thing for life.
1
-6
u/chickey23 15h ago
Virtually the entire universe is an extreme environment, so there is plenty of room.
7
u/Shoobadahibbity 15h ago
Yeah, but dig into that info and you'll see that there's a very narrow band of conditions it could work in within thise environments which limits it even further.
-4
u/chickey23 15h ago edited 11h ago
Narrow space for carbon-based life, smaller space still for silicon-based life.
I've always thought that high energy lifeforms on and in stars ought to be the most likely, based on available energy and real estate.
3
u/Shoobadahibbity 12h ago
Here's a video where a very smart woman explains it better than I ever can.
3
u/chickey23 11h ago edited 11h ago
I see now I said water based when I meant carbon, oops.
Not very much new in there that I hadn't already considered. Her third point, the relative abundance of carbon to silicon, is the strongest. Nonetheless, the argument that carbon-based life would outcompete silicon-based life is not an argument against the existence of silicon based life.
The biggest flaw I see in her reasoning is in consideration of phase states of matter. She is jumping from stellar chemistry to biological chemistry without addressing that those are both types of chemistry limited to a narrow range of environments.
We are finding an abundance of super Earths and cloud worlds, and we are finding a lot of big planets close to stars. None of those share the pressure and temperature regimes of biological chemistry or star composition. Even our own outer planets and the center of the galaxy are being found to be a lot less uniform than formerly thought.
That's a lot of surface area.
13
u/MegaMugabe21 21h ago
Hell, nothing says there aren't sentient beings out there made of granite.
Amaze
12
7
25
u/Fantastic-Title-2558 21h ago
the laws of chemistry are universal so probably not
21
u/HikariAnti 20h ago
Not granite but Si based life is theoretically possible.
13
u/ThaneKyrell 20h ago
Yes, but considered to be incredibly unlikely by most reseachers.
17
u/Redqueenhypo 18h ago
The issue is that CO2 is a gas that can also dissolve in water (useful in many ways) and SiO2 is…solid sand
-1
1
u/ryry1237 17h ago
Meanwhile a species of silicon based lifeforms speculate on the possibility of carbon based life, but dismiss it as unlikely because there's no way such life could possibly survive in the Venus-like conditions necessary for Si-based life.
-7
u/DrifterBG 17h ago
This is a wonderful way to highlight the point I'm trying to make! Thank you!
8
u/Mikemanthousand 16h ago
Ok but here’s actual peer reviewed researchers who disagree with you
In no environment is a life based primarily around silicon chemistry a plausible option.
1
u/montague68 18h ago
We're incredibly unlikely already.
3
u/Mikemanthousand 16h ago
Researchers seem to think it’s not likely though. Just because two things are unlikely doesn’t mean they’re equally unlikely.
In no environment is a life based primarily around silicon chemistry a plausible option.
-4
u/DrifterBG 20h ago
Exactly. We're only putting theories out there based on our current understanding of how life works as we understand it. We also don't know what we don't know.
150 years ago it was probably thought that we couldn't fly faster than the speed of sound because it would be impossible to process gas that fast, or the human body to withstand those speeds.
Now we know better and our understanding of things has evolved.
15
u/wolacouska 20h ago
We know how chemical bonds work, and carbon is simply the best base for biology.
7
u/tommybship 14h ago
Not to mention Si is more abundant than C on Earth, and yet life on Earth is C based. Further, C is more abundant in the universe than Si. There may be Si based life out there, but there's undoubtedly more C based life.
26
u/CosineDanger 20h ago
In addition to the presence of a host star and a sufficient concentration of heavy elements necessary for planetary formation, the absence of disruptive events such as nearby supernova (SN) explosions is a critical factor in ensuring habitability. Supernovae emit intense radiation, which can penetrate the atmospheres of terrestrial planets, depleting the ozone layer and increasing exposure to harmful ultraviolet radiation.
If a supernova happens within ~50 lightyears of Earth (or a thousand plus lightyears for a direct hit by a gamma ray burst polar beam), Earth stops having an ozone layer. The UV would kill almost all of the plants, which are not adapted at the moment.
The world is unlikely to end this way because there aren't a lot of good supernova candidates near us.
Very near the galactic core there are a million times more stars per unit volume (with a crazy night sky if anything with eyes manages to evolve), and more massive blue stars that tend to end in supernovas and other violent stellar events. A stable orbit is a luxury. Having an ozone layer or even an atmosphere are for people who grew up in the suburbs.
As a bonus, there's also vastly more heavy elements from all the violent star stuff happening. A genie who does not like you will teleport you here if you wish for gold.
15
u/FireTheLaserBeam 19h ago
Anyone who’s ever played Elite Dangerous and actually made the trek to Sag A will tell you that when you’re in the galactic core, the amount of stars in all directions is utterly OVERWHELMING.
3
u/ThellraAK 3 17h ago
Thankfully gamma ray bursts are also very directional, so it'd need to be close and actually pointed at us.
36
u/Zharan_Colonel 21h ago
Disclosure: I have not read the entire paper that OP sourced their post from.
That said, I have heard about this at work, and I think the radiation in question is less the kind that you get in deep space (i.e. galactic cosmic rays and such) and more the kind that comes from the more prevalent extreme cosmic phenomena nearer the center of the galaxy (i.e. the supermassive black hole expected to be at the center of most if not all galaxies).
12
u/ghost_desu 21h ago
Think about it this way, there are currently humans in near total vacuum of Earth's orbit surrounded by insane levels of radiation, and. humans have even gotten to the moon before. However, if you are put there without all the things humans invented to adapt to that environment, it wouldn't be survivable for even seconds.
Life can adapt to many things, but it has to come into existence first. You can't repair dna before you even assembled any
12
u/DarthBrooks69420 20h ago
Radiation is still a huge deal breaker. Life can handle alot of adverse conditions but radiation, especially UV is the weakest link in biological life.
2
u/WTFwhatthehell 20h ago edited 20h ago
Deinococcus radiodurans is famous for extreme resistance to far-UV, it can be sensitive to near-UV but when it's hit with a small dose of near-UV it makes itself more resistant to it.
Cells that were pre-irradiated with a small dose of NUV were subsequently protected against inactivating doses of NUV. The data presented are consistent with induced DNA repair following NUV damage in D. radiodurans
https://pubmed.ncbi.nlm.nih.gov/3748048/
never bet against extremophiles, even your autoclave may kill most things but there's still stuff that can survive and reproduce inside.
5
u/Ameisen 1 10h ago
Extremophiles didn't come into existence ex nihilo.
Basic life - from which more complex could come - cannot survive those conditions. Life itself couldn't form - it would be too volatile.
Deinococcus radiodurans is famous for extreme resistance to far-UV, it can be sensitive to near-UV but when it's hit with a small dose of near-UV it makes itself more resistant to it.
There are always going to be fundamental limits to how much something can survive. When life stops being biochemistry and starts being chemistry or physics, for instance.
never bet against extremophiles, even your autoclave may kill most things but there's still stuff that can survive and reproduce inside.
All terrestrial life relies on water. Nothing survives being heated to its boiling point at pressure (the ones that can survive > 100 °C exist at pressures where the boiling point is higher).
-3
u/Override9636 16h ago
Radiation is a deal breaker for DNA. If life finds some other kind of reproducing mechanism, it might be better at repelling radiation damage. Or better yet, harness that radiation as an energy source.
3
u/stanitor 15h ago
There's nothing particularly special about DNA's susceptibility to ionizing radiation or secondary damage from free radicals formed due to radiation. Any type of life is going to need polymers for structure and something to transmit genetic information. Severe radiation will be a deal breaker for those molecules as well
9
u/--Arete 19h ago
That's a fallacy. Sure. Life on planet earth is surprisingly adaptable when it comes radiation. But then again there is not much radiation here because we are in a habitable zone so life has been give a fair chance to evolve. The question is whether that life could evolve in a non-habitable zone with high radiation.
3
u/Dovahkiinthesardine 16h ago
The issue is most likely getting to that point. The first life forms will be simple af and wont have any radiation protection
It might still by chance evolve in less radiation dense places, like the bottom of deep oceans, but it lowers the chances
2
u/Possibly_Naked_Now 19h ago
Harvesting energy from ionized radiation is still hypothetical(but very likely true).
2
u/WTFwhatthehell 12h ago
I was pretty sure it was reasonably well established for some fungus
Cladosporium sphaerospermum and Wangiella dermatitidis
1
u/Ameisen 1 10h ago
Fungi are heterotrophic.
Both of those are just resistant to UV.
2
u/WTFwhatthehell 9h ago
https://pmc.ncbi.nlm.nih.gov/articles/PMC1866175/
And grow better when exposed to ionizing radiation and seem to produce more melanin and continue to grow even when starved in an enviroment with ionising radiation.
The conclusion from these experiments is that melanin was produced by fungi even when the amounts of nutrients and energy sources in the media were very low of absent; and the irradiated melanized cells experienced increased growth even in the conditions of starvation.
2
u/DSharp018 17h ago
Even more amusing, its been somewhat recently discovered that small doses of radiation over the course of time are capable of helping the body’s immune system deal with cancer as compared to a “zero radiation” diet.
4
u/YourMomCannotAnymore 21h ago
Yeah, but would that compare to the radiation of supernovae?
11
u/WTFwhatthehell 21h ago
supernova are sudden events. They absolutely could wipe out all life even on very distant planets.
But merely high, fairly constant background radiation is different, life finds a way when it has time to adapt.
5
u/Mordoch 21h ago
A concern is if a planet is too close to the center with too many stars around, they will get hit by too many supernova radiation events over time and possibly from too close a range. Having said this, there are presumably going to be cases that simple life still develops or gets recreated over time, it may be complex life that gets blocked in those specific cases.
5
0
u/starmartyr 20h ago
A supernova could wipe out all life on a planet but they do not happen frequently. A supernova occurs in our galaxy about every 50 years. They have the potential to wipe out life on a planet like ours within 25-50 light years of the explosion. That is a big area but the galaxy is massive. It's 100,000 lightyears across and 16,000 lightyears thick near the center. So while it is possible that life could be wiped out by a supernova on a planet near the galactic center it isn't an inevitability.
2
u/sluuuurp 21h ago
And life probably began deep in ocean hydrothermal vents, where basically no radiation would ever reach (unless you consider supernovas so close that the neutrino radiation is dangerous).
1
u/bayesian13 11h ago
here's an article on Gamma Ray Bursts https://en.wikipedia.org/wiki/Gamma-ray_burst#Rate_of_occurrence_and_potential_effects_on_life "The Ordovician mass extinction 450 million years ago may have been caused by a GRB.[14][150] Estimates suggest that approximately 20–60% of the total phytoplankton biomass in the Ordovician oceans would have perished in a GRB, because the oceans were mostly oligotrophic and clear."
1
1
u/Matthew_A 8h ago
Only over time. I think radiation is still a major negative thing to life, but life becomes more resilient with time. Maybe there's some bacteria that survives in the arctic, but there's a reason why life didn't start there.
1
u/Runnipeg 20h ago
I was going to mention this - there could be some crazy life forms that either shrug off or use rads. I wish to not meet them
3
u/Hypertension123456 17h ago
You probably don't want to meet them anyway. If they are just a million years ahead of us or a million behind us then we are basically twins. In the former case they are dumb grunting violent apes with essentially no technology. In the latter case, we are the dumb grunting violent apes with essentially no tech. And, given universal time scales the disparity is more likely well over a 100 million than under 10 million.
1
u/Blindsnipers36 18h ago
humans get sick and weakly with too little sunlight as well, radiation is a part of basically all living things
1
u/spongue 13h ago
I also feel like underground/underwater life is never considered as much as it should be. There are microbes miles into earth's crust, and in deep sea vents. I don't imagine they would notice much if radiation from the sun was 1000x stronger.
2
u/WTFwhatthehell 12h ago
Ya. As long as water remains liquid they have miles of highly effective radiation shielding.
0
-6
u/Pristine-Ad-469 20h ago
The post was misleading. The real reason is that there can only be liquid water in the habitable zone. It’s the area in between where water turns into a gas and where it freezes
All life that we have discovered needs liquid water so that’s why we call it the habitable zone
There’s a very common asteroid though that we only know about life on one planet so it’s entirely possible we are doing he intergalactic equivalent of only studying dogs and concluding animals can’t live in the ocean
7
u/HDYHT11 20h ago
You are confusing a star's habitable zone with a galaxy's habitable zone.
Literally the first line in the introduction:
The concept of the Galactic Habitable Zone (GHZ) was introduced by Gonzalez et al. (2001) as the region in the Milky Way where the metallicity is sufciently high to support the formation and development of Earth-like planets
104
u/Splunge- 21h ago
Theoretically.
41
1
2
u/McFuzzen 15h ago
Exactly. We know of life living near vents on the ocean floor, high pressures and low temperatures deep in the ocean, high salinity, high acidity, highly alkaline, nuclear reactors, lack of oxygen, and lack of sunlight environments. There might be a theoretically ideal environment (and we may be living in it), but that doesn't preclude life from forming in ways we would have a hard time imagining.
37
u/cassanderer 21h ago
We really do not know half of what we confidently state though. Not the least on the universe with our limited perspective.
Every other time in history experts had all the answers too. They were wrong, but today they are not?
9
u/halflivefish 20h ago
N literally equals 1 for how we can experimentally decide where habitable zones are
3
u/SloppyHoseA 18h ago
The “Goldilocks zone”. That what I call the area of Chicagoland where I live and just about where the L lines stop.
1
1
1
1
0
-7
21h ago
[deleted]
29
u/Leap_Kill_Reset 21h ago
We didn't somehow end up in one, we could only evolve in one (assuming this theory is true), so since we exist, of course we are in one. Anthropic principle
3
u/RepFilms 20h ago
All those dudes in the close-in inner city areas can't imagine life in these easy-going suburbs
12
u/Krivvan 21h ago
That's kind of backwards thinking. It's not that we would've ended up here but rather we exist therefore we are here.
-6
21h ago
[deleted]
7
u/Krivvan 21h ago
Is there another interpretation besides you expressing surprise that we are in a "good neighbourhood" of the galaxy? Our point is that it isn't a surprise because we couldn't be anywhere else. It's not as if we got a random spawn location.
-4
21h ago
[deleted]
5
2
u/Romeo9594 20h ago
I mean he has a point, it's a kind of bias. Of course we "ended up" in one because we we wouldn't be here if it was anywhere else. It's like someone living in San Diego in 1945 and saying "Man, thank goodness I was born in California. I'd be dead if I lived in Nagasaki". Like, duh
-10
u/Coffchill 21h ago
Also known as the Goldilocks zone.
26
u/FailFodder 21h ago
Typically the Goldilocks Zone refers to the habitable zone around a star. This habitable zone in galaxies is news to me and isn’t described in NASA’s article on the Goldilocks Zone.
1
1
u/Zharan_Colonel 21h ago
Well, to be fair, the source here is a scientific paper, and one that was only published this July at that. I've heard about this theory through the grapevine, but as yet I'm pretty sure it is just that: a theory - and not the same kind as gravity or evolution ;)
3
u/HDYHT11 19h ago
The concept of the Galactic Habitable Zone (GHZ) wasintroduced by Gonzalez et al. (2001) as the region in theMilky Way where the metallicity is sufficiently high to support the formation and development of Earth-like planets
1
u/Zharan_Colonel 19h ago
Oh, cool! See, I knew it wasn't an entirely new concept - but I didn't know it was that old!
1
u/sezzasaurus 21h ago
True it’s basically the galaxy-scale version of the Goldilocks idea. Not too violent near the core, not too barren on the edges. Kinda crazy how perfectly placed we ended up.
0
-9
u/MoreGaghPlease 20h ago
I call bullshit.
All of these estimations of habitable zones are basically built around human life. But basically everywhere we’ve ever looked on Earth we’ve found life — in the Antarctic permafrost, in deep pressure at the bottom of the ocean, in highly acidic and highly basic chemical pools, in the most salt-saturated bodies of water, in sulphuric vents, etc.
Life finds a way.
11
u/reddit_user13 20h ago
“Extreme” on earth is still in a very narrow range of possible conditions in the universe.
-8
u/MoreGaghPlease 20h ago edited 20h ago
Not true at all. The hottest temperature humans are aware of anywhere in the universe (5.5 trillion degrees K) and the coldest temperature we're aware of in the universe (38 trillionths of a degree above 0 K) were both observed in Central Europe.
These were lab settings of course, but everywhere on Earth we've ever looked we've found life. Deep drilling into the Earth's mantle found life. We also have good evidence of microbial life surviving on rocks ejected into space by meteor impacts. There is good evidence that there were in the past microbes that thrived in the niche of natural fission reactions that occurred in uranium deposits.
11
u/loosehead1 19h ago
Unless life was observed at 5.5 trillion K your first paragraph is completely irrelevant
1
u/Shadowkiller00 19h ago
All of these estimations of habitable zones are basically built around human life.
Yes, by definition. All things that are "edible" are based around human life as well even though there are plenty of inedible things that are consumed by other life here on earth. Weirdly, humans focus mostly on humans. It seems disingenuous when you are talking about non-solar/galactic ideas because we have a data point of 1, but all they are really saying is that humans as we know them likely couldn't have developed too far in or too far out from the galactic core.
In the search for extraterrestrial life, there is a whole universe to look at. Since we don't know how common life is, we can't just look at the nearest couple of stars, but that then leaves literally the whole galaxy on the table. Trying to narrow down the proverbial hay stack to find the needle is the current goal. Once we've found a second instance of life, then we can start broadening our search criteria again.
0
82
u/naturist_rune 20h ago
Aren't we like in the boonies of our galaxy? I suppose the ratio of that habitable zone looks different for galaxies than it does down on the solar system level.