You've probably heard the Oasis song Black Dwarf Supernova - but did you know it was a real thing?
More precisely, none exist *now*, but they may be among the last really exciting events in our universe. As a star the size of our Sun dies, it eventually shrink downs to a white dwarf, very hot and dense but held up by 'electron degeneracy pressure'. That's because electrons can't be in the same quantum state.
As a white dwarf cools, we expect it will dim and eventually become a 'black dwarf'. This hasn't happened yet. While there are already plenty of white dwarfs, they take a long time to cool down. The coldest white dwarfs found are about 12 billion years old, and they're still 3,600 °C. We expect that for a white dwarf to get *really* cold, like 5 °C above absolute zero, would take about a quadrillion years!
But before that happens, it could explode.
The reason is that as it cools, its electron degeneracy pressure gets smaller and it shrinks. For white dwarfs heavier than 1.2 times the mass of our Sun, this may actually tip them over into collapsing entirely, becoming black holes. But just as with heavy stars today, this collapse should also liberate a huge amount of energy, shooting off the star's outer layers in a SUPERNOVA!
Stars that could do this account for just 1% of all stars in the observable universe. But that's 10²¹ stars - nothing to sneeze at.
These black hole supernovae may go off around 10¹¹⁰⁰ years from now, long after most other processes have settled down. However, it's possible that the protons in these stars will decay first. Protons could be stable, but we only know for sure that their half-life exceeds 10³² years.
@johncarlosbaez So, the long-term plan for bio-life is to get really cozy with a white-dwarf and travel the ages with it!
@flq - alternatively, red dwarf stars considerably smaller than our sun keep going for 100 trillion years and have earth-like planets which we might maneuver into the habitable zone. Right now many have annoying flares, but as they age they probably settle down. I've advertised them here:
https://johncarlosbaez.wordpress.com/2015/02/14/earth-like-planets-near-red-dwarfs/
@johncarlosbaez very interesting! Wikipedia has a list of the far future events in the universe, and that one is mentioned: https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future
Gee, I dunno. I have the same fantasy, but...
Between being a flare star (radiation nightmare), flares likely blasting away any atmosphere, tidal locking from having to be so close... that's a life-hostile environment.
Unless it's underground, or maybe under ice in a water world.
Both of those seem to argue against evolving life that will look up at the stars very much. For them, the sky would be *dangerous*.
That leaves troublemaker refugees like us, migrating to red dwarf systems to live underground. And interstellar travel is *hard*.
And don't even get me started about the financial and banking issues raised by Paul Krugman in his "Theory of Interstellar Trade" monograph. :-)
@davidsuculum - yes! I urged the Wikipedia editors to take down an entry here about Falcke et al's claim that black dwarfs would disappear due to Hawking radiation, and I see that's happened.
@johncarlosbaez
Possibly silly question. You state that `a planet needs to be close to a red dwarf to be warm enough for liquid water`. Couldn't the gravitational contortions, from the three suns, maintain enough geological activity to keep it warm enough for surface water?
IIRC Jupiter's Io is pretty warm due to gravitational fluctuation induced geological activity near the surface.
@nikatjef - you're talking about the three stars in the Centauri system. I could try to estimate the tidal heating created by Alpha Centauri A and B on a planet of Proxima Centauri, but since they're a quarter of a light year away, my physicist's gut sense says this effect is tiny. That's very far away. Proxima Centauri orbits those other stars once every 500,000 years or so!
@johncarlosbaez @flq somehow it's the "[humanity will] maneuver [planets] into the habitable zone" part of this I find harder to swallow than the "humanity will exist long enough and travel far enough to settle around a red dwarf star"
@earthshine - for me, the hard part to swallow is that humanity will survive long and enough and travel far enough to settle on a red dwarf star. If we can do that, I think that means we'll have our gotten act together - we sure don't now! But if we get our act together, there will be various ways to move planets around.
I haven't checked the calculation myself, but this website says if we can apply a force of 1 newton of force per square centimeter on the a planet the mass of the Earth, it will accelerate at 2.7 meters/second every year. If a civilization did that for thousands or millions of years, it would amount to quite a lot. With more patiences, less acceleration is necessary.
@johncarlosbaez @flq I mean there's a reason I found the thought notable. I don't expect we'll make it much further, myself, but the energy requirements to change the orbital period of a planet by any fraction of an AU are sufficiently high I can't imagine us actually using that energy for that even if we did somehow harness it in the first place.
The reaction mass alone, even in terms of fusion power, is bigger than anything we've built before.
@earthshine - of course it's vastly bigger than anything we've done so far! And I agree that it's probably a waste to even bother. But it's sometimes fun to think about the schemes people have come up with to move planets and stars around. In some crazy way stars are easier, because they have their own power source. Check out this Wikipedia article:
https://en.wikipedia.org/wiki/Stellar_engine
But if you move a star around slowly, its planets will simply follow, so that's not a way to change planetary orbits.
Besides energy constraints, we would also have a big problem that suns give off a bunch of energy that is essentially destructive to all forms of life we know of.
The Earth is uniquely situated because we have a magnetic field due to the molten core, but that same core is also a taking time bomb -- the continent of Australia it's mostly desert, completely unlivable, and in about 250 million years a new supercontinent will form which will be a mass extinction event that could include humans -- supercontinents end up dry and hot like Australia, at least that's what the models tell us will happen. So you have the power of the sun on one hand which will toast our DNA without the ionosphere, and you have the power of seismic drift on the other which will toast us due to most of the surface of the Earth becoming a giant unlivable rock -- and that seismic activity is a necessity because you need the molten core to protect life on Earth. On the other hand, it's not the only thing that we have to worry about including core cooling, and solar brightening. A cosmic fist will eventually close around the planet Earth.
Really helps you understand how fragile life is, and how lucky we are to live in this particular moment in the history of our planet.
Within what I'm talking about, Mars will eventually enter the habitable zone, but it will remain impossible to live on because it has no core. I guess if we had enough time and unspeakable amounts of energy to reactivate Mars's core, but again you're probably talking about so much energy if you had it you might not need the Sun.
Now if you'll excuse me, I'm going to go cry in the corner for the rest of my life.
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@weekend_editor - Your points are all valid in the short term. I was proposing red dwarf stars as a place for civilizations to settle down after a few billion years. Remember they're expected to last 100 *trillion* years. So, they might make good old age homes for ultra-advanced civilizations that want a long-term power source.
I don't know for sure, but I suspect flare stars will gradually calm down as they get older. So I believe they probably won't be flare stars after a few billion years... or a few hundred billion years...
Of course, we don't really have a clue what will happen that far in the future. But it's fun to dream sometimes.
The rocks will absorb the sulfur.
There's evidence that the core of Venus is still molten since one reason for all the SO2 seems to be volcanic eruptions, but there's only a very weak magnetic field that doesn't seem to be caused by the core. This seems to be because Venus has an insanely long day -- over 200 earth-days.
The lack of spin also could be the reason why Venus appears to lack plate tectonics, since the lack of spin results in a much more stagnant core.
Venus famously has quite a lot of Sulphuric Acid (H2SO4) in its upper atmosphere which does in fact deteriorate into SO3 and H2O, but the H2O is broken up into H and O by UV, and then whatever H and O arrive are basically stripped away by solar wind, keeping the planet super dry. Get a magnetic field, and you could start seeing water in the atmosphere again, which would also help reduce the greenhouse effect.
In the end, it might make more sense on a geographical timeframes scale to look at Europa instead. Mine through 40km of ice, and you find yourself in an endless ocean heated by orbital forces to just above 0C, leaving you with a temperature gradient you can use for energy generation, as well as a moon worth of water. As the sun expands into a red giant that region would even become part of the habitable zone for a few hundred million years before freezing once again and potentially remaining basically as it was until orbits go wonky. Having 40km of ice above you sounds claustrophobic, but given that you'll need to survive the radioactivity of space, it might not be such a bad deal.
I assume our form of underwater mining might be like a baleen whale, just purifying water and keeping whatever we find.
And since the crust is deep but also just water, you'd just need to send over something that makes heat consistently -- An RTG is one option, but also a small scale nuclear reactor, just melt melt melt and eventually you're underground.
It's not a very nice life, mind you. It's basically living in low gravity high pressure enclaves for a trillion years that are likely to be essentially pitch black. There's CO2 on that moon, however, and it's possible that there's ammonia, and if that's the case then you can have a hard life that can nonetheless exist without requiring solar system class levels of energy such as would be required for moving planets or kicking Venus into a spin (and unlike Venus, the Europa plan would survive the end of the Sun)
Over a trillion years of surviving on Europa, you could also have humans evolve or evolve themselves into something more suited to the environment -- After far less than a million years I'd suspect we'd have figured out far length IR vision, probably pressure proofed our bodies, maybe even given up on breathing gasses and just oxygenated water within our habitats. At that point, it's just a matter of conserving elemental carbon and nitrogen and producing oxygen and maintain the energy collection via the gradients between the surface and underground -- You might not even need to hit surface, presumably you could find a way to utilize temperature, pressure, or salinity gradients under the oceans to produce energy.
One thing is that the 40km ice wall means evolution would be slow down there I bet -- Even gamma rays don't like 40km of ice. It's probably radioactively dead as a doornail.
Crazy to think though, if life exists somewhere out there, is there another species that took this path?
@johncarlosbaez Cool post, but the Oasis song is “Champagne Supernova”.
@AstroMikeHudson - I was waiting for someone to point that out.
I know. That was a joke. It sounds better if you sing it "Black Dwarf Supernova".
@AstroMikeHudson @johncarlosbaez I ended up singing Oasis to myself for a lot of yesterday (this song, but also Don’t Look Back in Anger) which was not altogether unpleasant. I’ll look forward to the next time you post about a Supermassive Black Hole.
Over time, the acid would react with rocks to make sulfate minerals such as gypsum.
But we will probably never control enough energy to move it into a higher orbit.
As for Europa, I don't think the pressure in its ocean is very high (don't know exactly how high, but..) -- Gravity is much lower on Europa because it is small. Of course Jupiter may have more influence over its climate than the Sun. We may soon learn what is inside it, no doubt it will be interesting.