When the last sun dies, could life continue by creating a star?
Sorry, I have to be the contrarian here.
When the last star in the universe ceases fusion under its own gravity, it is not necessarily the end of stars.
About 97% of stars in the Milky Way, and probably a similar number throughout the rest of the universe, will end up as white dwarfs. A white dwarf is a star that cannot fuse carbon or oxygen, and maybe not even helium if it is below about half a solar mass.
Moreover, there are a very large number - about 70 billion in our galaxy - of brown dwarfs, objects between the size of Jupiter and 7% of the size of the Sun, which cannot fuse hydrogen.
This means that when that last star burns out after its natural lifetime, there will be a large number of failed stars (the brown dwarfs) with lots of hydrogen and dead stars containing unfused helium, carbon and oxygen. In order to use these fuels, a very advanced cilization could consolidate these objects into more massive objects, which would reignite the fusion process. And voila! You have new stars.
Of course, you can only do that until you turn everything into iron. But, if these newly created stars are massive enough, they will eventually collapse into black holes. Black holes (theoretically) emit Hawking radiation as they evaporate. This Hawking radiation could then be used as an alternative energy source, and could last for a very long time.
No. I'm only answering to compliment Franklin Voox's sagacious answer. You may or may NOT already know this, but by the time the last star actually dies, literally trillions and trillions of years will have passed. I believe it was Dr. Brian Cox (yeah, I know, he's not beloved by everybody) provided a reasonable comparison for this. The stage we are at (13.75 billion years) in the total life of the cosmos before the heat death takes place will be equal to less than the first pico-second of time during the big bang to our 13.75 billion years. How many seconds have gone by so far? We are in that -the first second- when compared to the ultimate length of time our cosmos will exist.
There won't be a "we" at that point in time. If some distant descendant of ours exists at that long-scale time down the road (10,000-trillion-trillion-trillion-trillion-trillion-trillion-trillion-trillion-trillion years† ... I believe was the number he gave), it will be so different from us that we cannot even imagine, imagining how they will behave or what they will want. . Even then, it's doubtful they could reverse the heat death of the cosmos. They too, will perish.
- Dan Holliday & Franklin Veaux are right that once the universe's hydrogen and helium are used up, there are no more practical possibilities to create new stars. That could be the end of whatever sentient life is left.
- Daniel Merthe is right-even if all stars that reached the critical mass needed to convert hydrogen to helium went supernova, or shed their outer layers like our sun will, there are still lots of brown & white dwarfs left over that you could collide and create some more energy out of.
So given that the answer is 1) no because no fuel is left, and 2) yes if you take unused fuel from other sources, we can venture just a little bit further than the scope of the question and add that even then, there other are ways to use dead stars to provide energy.
The biggest way might be to throw a bunch of matter around a black hole and take the radiation generated when the accretion disk is subjected to intense gravity and friction. I think the concept comes across in Deep Time by David Darling, where towards the dark age of the universe, whoever is around, basically throws their trash into the dark pit and gets a brief stream of energy to keep on going before hibernating and repeating the process.
Stars of around solar mass will end up as white dwarfs. So after billions of years hydrogen burning while they are on the ‘Main Sequence', they will swell up to become red giants, eject outer material to form ‘Planetary Nebulae', and leave behind the naked core of the star, a white dwarf.
Here is the thing. The white dwarf has a lifetime of TRILLIONS of years.
So we would expect advanced civilization* might migrate to white dwarfs, and get a new...very long... lease of life.
*Assuming war/plague/religious regression/asteroid impact/superflares/gamma ray bursts/nearby supernova/quasar activity at galactic core/the red giant stage of their own star didn't destroy them first. Carl Sagan used to preach that in the long term, advanced civilizations would be spacefaring or extinct:).
We have no idea what life will be like in just a few hundred years, let alone billions. We are on the cusp of genetically modified humans, human-machine hybrids and fully artificial life.
Humans have been around for a tiny, tiny amount of time compared to the age of the universe and change is accelerating. We have no idea what life - whatever it is - will think and want in billions of years. It won't be what we call humanity. It will look different and have different concerns.
Will whatever it is be interested in creating stars? Who knows. This is a little like cave men wondering what people will eat in 30,000 years when all the mammoths are gone. Things move along, and, on this time scale, things move completely out of sight.
In addition, the laws of physics are not well enough understood to predict this brown-out trap picture with certainty. The Big Bang - a sudden appearance of an entire low entropy universe - suggests that there potentially may be other options for the survival of life, if that is considered desirable at the time.
Humility suggests we can leave this question to be figured out when required. By whatever is around at the time. Using vastly superior capabilities and knowledge.
When the Sun dies about 5 billion years from now it will not simply
When the last sun dies, what will you make the new star out of? By that point, there will be very little hydrogen left.
Stars fuse hydrogen into helium, helium into carbon, and so up the chain to iron. Past iron, you no longer produce energy by fusion, it requires energy.
That means that the hydrogen, helium, and other light elements in the universe are gradually being ‘used up,' turned into iron and other things you can not extract any energy from.
When all the hydrogen is gone, it's adiós, muchachos. You have nothing left to make a new star out of.