Complex life may be possible in only 10% of all galaxies

Dec 1, 2014

NASA/SWIFT/MARY PAT HRYBYK-KEITH AND JOHN JONES

By Adrian Cho

The universe may be a lonelier place than previously thought. Of the estimated 100 billion galaxies in the observable universe, only one in 10 can support complex life like that on Earth, a pair of astrophysicists argues. Everywhere else, stellar explosions known as gamma ray bursts would regularly wipe out any life forms more elaborate than microbes. The detonations also kept the universe lifeless for billions of years after the big bang, the researchers say.

“It’s kind of surprising that we can have life only in 10% of galaxies and only after 5 billion years,” says Brian Thomas, a physicist at Washburn University in Topeka who was not involved in the work. But “my overall impression is that they are probably right” within the uncertainties in a key parameter in the analysis.

Scientists have long mused over whether a gamma ray burst could harm Earth. The bursts were discovered in 1967 by satellites designed to spot nuclear weapons tests and now turn up at a rate of about one a day. They come in two types. Short gamma ray bursts last less than a second or two; they most likely occur when two neutron stars or black holes spiral into each other. Long gamma ray bursts last for tens of seconds and occur when massive stars burn out, collapse, and explode. They are rarer than the short ones but release roughly 100 times as much energy. A long burst can outshine the rest of the universe in gamma rays, which are highly energetic photons.

That seconds-long flash of radiation itself wouldn’t blast away life on a nearby planet. Rather, if the explosion were close enough, the gamma rays would set off a chain of chemical reactions that would destroy the ozone layer in a planet’s atmosphere. With that protective gas gone, deadly ultraviolet radiation from a planet’s sun would rain down for months or years—long enough to cause a mass die-off.

How likely is that to happen? Tsvi Piran, a theoretical astrophysicist at the Hebrew University of Jerusalem, and Raul Jimenez, a theoretical astrophysicist at the University of Barcelona in Spain, explore that apocalyptic scenario in a paper in press at Physical Review Letters.


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23 comments on “Complex life may be possible in only 10% of all galaxies

  • Even if 90% of the galaxies are inhabitable, that still leaves 10 to 20 billion. And when you consider the billions of stars in each galaxy, that provides plenty of opportunity for complex life.

    A favorite quote of mine from Carl Sagan’s “Contact”:

    “The universe is a pretty big place. If it’s just us, seems like an awful waste of space.”



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  • You need to make a distinction between life starting in such galaxies and life existing in such galaxies. Intelligent beings can modify their environments to live pretty well anywhere.

    Also we have only a few examples of intelligent species and only one example of a technological species. It is premature to extrapolate with any certainty from that to make up rules about the limits of all intelligent species. We are just a baby intelligent species. If we don’t go extinct, with even another 100,000 years, our limits will surely have expanded beyond our current wildest imagination.



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  • This reflects one of my recurring nightmares. What if we are the only self aware intelligent life in the universe, and we commit species suicide through stupidity. Where then Asimov’s Foundation.



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  • There is a lot of wish-thinking about extra-terrestrial life.

    Not only are some ancient small globular galaxies lacking in heavy elements (such as carbon and oxygen) – [Low metalicity], due to a lack of large stars going supernova and hence a lack of second generation stars, but large galaxies like the Milkyway have fierce radiation and massive gravitational turbulence near their centres.
    There is also the likelihood of regular severe radiation bursts in clusters near large stars going supernova in sequence.

    However, the Solar-System is in an area of high metalicity, so nearby star-systems within possible range of our probes, are likely to have similar chemistry to ours.



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  • 5
    Lorenzo says:

    What if we are the only self aware intelligent life in the universe

    I think there are plenty waiting in the line on this planet alone -if we manage not to drive them extinct. Dolphins, chimps and bonobos, elephants… I’d love to see what the situation will be, on this planet, in half a million years. After all, modern cognition level among humans are terribly recent: a few hundreds of thousands of years. That’s really nothing.



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  • 6
    Lorenzo says:

    A problem I see with this kind of estimate (at least, before reading the article… but that’s unlikely to happen, since my day will hardly grow a 25th hour in the near future) is chronological in nature: how did they compensate for that -if they did it at all?

    Because, the further away you look, the more in the past you see. Thus, most of the galaxies you can observe today are now billions of years further in their development, as far they are concerned… So I’m not really convinced that now 10% of the galaxies are hospitable for complex life -mostly because “now” is a pretty meaningless word when used to describe the observable universe. What I’d expect to read is that, averaging on a give span of time, the probability for a galaxy to be hospitable is around 10%… which is less interesting than having a probability distribution for being hospitable for complex life. And I would expect that distribution being around 0 at the beginning, staying there for quite a while and then rise -and, eventually, reaching values not so far from 1?

    Still, even if it turned out to be true that “only” 10% of the galaxy are hospitable for complex life, and if it turned out that of those only 10% actually do, the universe would be hosting a huge, huge number of species with cognition capabilities similar to ours. I’d find hard to believe us being alone even if only one galaxy in a million would be hospitable to any form of life at all…

    That’s why: let’s take a reasonably rare event, say one that has a half life of 10 to the 20 seconds. That’s a long time, by the way. If you take, though, 10 to the 18 candidates for that event, you can expect to observe that event once every 100 seconds… and that’s about one every 2 minutes. That’s the effect large number have on rare events…

    That should also give you an idea of how bloody rare GRB are, since you observe just one per day in a place as vast as the universe!



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  • Lorenzo Dec 2, 2014 at 5:38 am

    A problem I see with this kind of estimate (at least, before reading the article… but that’s unlikely to happen, since my day will hardly grow a 25th hour in the near future) is chronological in nature: how did they compensate for that -if they did it at all?

    I’m not sure what point you are making, but while your day will only change by fractions of a second, the Earth’s day will in time “grow a 25th hour”!

    http://www.scientificamerican.com/article/earth-rotation-summer-solstice/

    Corals, for example, go through daily and seasonal growing cycles that form bands akin to growth rings in trees; counting them shows how many days passed in a year. In the early Carboniferous period some 350 million years ago an Earth year was around 385 days, ancient corals indicate, meaning not that it took longer for the planet to revolve around the sun, but that a day–night cycle was less than 23 hours long.

    Sedimentary rocks such as sandstone also testify to the quicker days of yore. As moon-spawned tides wash over rocks they deposit mineral specks, layer upon layer. In southern Australia, for example, these vertically accumulating tidal “rhythmites” have pegged an Earth day at 21.9 hours some 620 million years ago. This equates to a 400-day year, although other estimates suggest even brisker daily rotations then.

    Most computer simulations of this explosive lunar genesis suggest that Earth whirled afterward on its axis every six hours, says Jay Melosh, an Earth and atmospheric scientist at Purdue University. As the moon has migrated out from an initial tighter orbit of perhaps 25,000 kilometers to the modern average distance of 384,000 kilometers, it has teamed up with the sun to protract Earthly days fourfold.

    Units of time can indeed be misleading in astronomy.



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  • Firstly, I wrongly reported this comment (OOps, sorry for that).

    Secondly. ‘You need to make a distinction between life starting in such galaxies and life existing in such galaxies.’

    Not really, in order for intelligent life to exists in such places it has to start, if the events in the article take place often enough to wipe out anything other than simple, very early life then intelligent beings are never going to get the change to adapt to anything.

    13 billion years later and intelligent life here on earth is almost brand new.



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  • I think Roedy’s point is that a galaxy in which intelligent life couldn’t evolve, because gamma ray bursts wipe out simpler life too soon, is nonetheless one to which intelligent life could move from a different galaxy, using their technology to survive subsequent gamma bursts. I was unsure whether I should have this a reply to Roedy or to veggiemanuk, because I have my doubts about how common or viable such intergalactic relocation would be. Even if civilisations can work out a way to travel millions of light years for colonisation purposes, economically they may not want to for a very long time, since there will be something like 100 billion stellar systems within 100,000 light years worth making use of first. So if only 10 % of galaxies can evolve intelligent life, I doubt anywhere near 100 % would eventually end up with either locally evolved or externally immigrating intelligent life. It’s very hard to compute exactly how much damage gamma ray bursts make to the number of galaxies (or solar systems) that eventually have intelligent inhabitants, but it’ll probably be a bit.



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  • 10
    Lorenzo says:

    the Earth’s day will in time “grow a 25th hour”!

    Yes I knew that, sadly it will never happen soon enough! The point I was making is: I currently have no time to read the article, sadly… and an extra hour per day, therefore, would come in very handy.

    The serious point I was trying to make in my whole comment is: because light’s speed is finite, the assertion “only 10% of the obsevable galaxies may be capable of supporting complex life” might not mean anything, because the concept of present, in the universe, does not mean anything.



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  • Jos Gibbons Dec 2, 2014 at 7:43 am

    I have my doubts about how common or viable such intergalactic relocation would be. Even if civilisations can work out a way to travel millions of light years for colonisation purposes, economically they may not want to for a very long time, since there will be something like 100 billion stellar systems within 100,000 light years worth making use of first.

    The distances are indeed generally problematical.

    The possible scenarios I can imagine, are where major galaxies (such as The Milkyway and Andromeda) collide and merge, or throw solar systems out across intergalactic space, or where satellite galaxies are drawn into larger ones on decaying orbits.

    As far as humans are concerned, we need to learn to manage the planet we have, develop interplanetary travel, and evolve this into interstellar capability, long before we can contemplate anything more ambitious.

    Any alien life would have similar limitations.



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  • Lorenzo Dec 2, 2014 at 7:52 am

    Yes I knew that, sadly it will never happen soon enough! The point I was making is: I currently have no time to read the article, sadly… and an extra hour per day, therefore, would come in very handy.

    One of the space agencies might be able to fit you up with an extra 39 minutes!
    http://en.wikipedia.org/wiki/Timekeeping_on_Mars
    The average length of a Martian sidereal day is 24h 37m 22.663s (based on SI units), and the length of its solar day (often called a sol) is 88,775.24409 seconds or 24h 39m 35.24409s.



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  • The concept of waste can only apply in a situation of limited resources. The Almighty by definition does not have limited resources, therefore what looks like profligate behaviour to us, is just an afternoon’s amusement to Him.



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  • Lorenzo Dec 2, 2014 at 7:52 am

    The serious point I was trying to make in my whole comment is: because light’s speed is finite, the assertion “only 10% of the obsevable galaxies may be capable of supporting complex life” might not mean anything, because the concept of present, in the universe, does not mean anything.

    I’m not sure that is the limiting factor.

    It seems unlikely that solar systems of first generation stars will have planets with the heavy elements needed for life, or if they will have any planets at all.

    For second or subsequent generations of stars to have planets with life-forming elements, there must have time for large first generation stars to go through all stages to a supernova explosion, and then second generation stars to form from the remnants.



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  • I have a question about the premise of this paper. It seems to me to be a bit human centric at first rub. Are they not making the assumption that intelligent life could only occur say above the surface of the ocean? My understanding was that a major threat of impacts of high doses of radiation from Super novas would be wiping out our ozone layer. Now this would effect us significantly but I don’t imagine it would take much ocean above you to be blocking the effects of this radiation out. What they are really saying is life as we know it could have only occurred like it has on Earth in this range. I’d go further and say life as it is on Earth could only happen here on Earth. Now I understand why we would concentrate our search for life around criteria that we know works and therefore this is a valuable contribution to that…..but something about these sort of statement make me wiggle and squirm. I keep hearing Feynman arguing that the universe has much more imagine than we do.



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  • 18
    Lorenzo says:

    It seems unlikely that solar systems of first generation stars will have planets with the heavy elements needed for life, or if they will have any planets at all.

    Absolutely. I was speaking about this in my original comment: a probability distribution over time for being hospitable for complex life rather than a blunt number, “10%”. That would be something really interesting to read… something less interesting but still correct would be the integral of said (unknown) distribution over some time span, which would be estimated at around 0.1 -and I suspect this is the case.

    But again: I should read the article to find out and, right now, I have some other articles to study…



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  • Of the remaining 10 % benign conditions must have endured for 5 billion years. That should pare it down even further.

    About the quote from Sagan

    “The universe is a pretty big place. If it’s just us, seems like an
    awful waste of space.”

    A waste for whom?

    Then there is is the question of distances. All this makes the search in vane IMHO



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  • Robert Dec 5, 2014 at 3:28 pm

    That’s what I thought too. 10% of Galaxies represents a truly astronomical number of stars.

    That leaves those with potential for life, very widely spaced apart – if they are evenly distributed.

    On the other hand, if the stars are in metal rich clusters, within “goldilocks zones” around certain types of galactic centres, there could be life-forms nearer to each other.

    http://www.astrobio.net/news-exclusive/galactic-habitable-zones/



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  • Olgun Dec 2, 2014 at 6:17 pm

    These guys can live almost anywhere

    I think they would struggle in the daylight here!

    Orbiting between 28 and 43 million miles (46 and 70 million kilometers) from the sun, Mercury, also the smallest planet, feels the brunt of the solar rays. The planet has an average temperature of 332 degrees Fahrenheit (167 degrees Celsius) The day side of the planet reaches temperatures of up to 801 F (427 degrees C). In contrast, the chilly night side can get as cold as minus 279 F (minus 173 C). http://www.space.com/18645-mercury-temperature.html



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