When will the last stars of the universe explode?

(ORDO NEWS) — The last interesting event in the universe will be the explosions of burnt-out stars, according to Matt Caplan of the University of Illinois. By that time, not only will there be no life, but also no black holes. The expert calculated when space would light up with farewell fireworks.

The results of his work are described in a scientific article accepted for publication in the Monthly Notices of the Royal Astronomical Society.

One day the stars will be gone

New luminaries are born from clumps of interstellar gas in galaxies. Throughout its life (and especially in its last stages), the star returns to the Universe a significant part of this debt, expelling matter from itself, which again becomes interstellar gas. In addition, some of the star’s mass is converted into radiation during thermonuclear reactions.

All other matter is concentrated in stellar remnants – white dwarfs, neutron stars and black holes. And this is the final death: such matter no longer has a chance to again become part of a star born from interstellar gas.

The white dwarf that the Sun will someday become will concentrate in itself about half of its mass. For most of the luminaries, the fraction of mass that forever “precipitates” in the form of a stellar remnant is even higher.

Sooner or later, there will be too little gas left in galaxies for the birth of new stars. And then the Universe will be enveloped in darkness. It will be illuminated only by the still incandescent but gradually cooling white dwarfs and neutron stars. In the end, they will also cool off.

“It will be a bit sad, lonely and cold place,” – Kaplan describes what space will become in old age.

Retired Star’s funeral pyre

However, according to the theorist’s calculations, before the final onset of eternal darkness, the world will have an impressive farewell fireworks display. The most massive white dwarfs will illuminate the Universe with the fire of thermonuclear explosions.

A thermonuclear explosion of a white dwarf (aka a type Ia supernova) occurs when its mass exceeds a certain limit. This critical point (Chandrasekhar limit) depends on the chemical composition of the white dwarf.

This usually happens if a celestial body gains mass. For example, a white dwarf can accumulate too much matter, “stolen” from a companion star, and disappear in a thermonuclear explosion (greed, as you know, does not lead to good). The same cataclysm can occur when one white dwarf collides and merges with another.

But the mass of white dwarfs in a cooled universe will not grow. Anything that might collide will already collide. All the stars from which one could “steal” matter will also burn out. What, then, can disturb the peace of the dead star?

The mass of such a celestial body really will not grow, the scientist answers. But the chemical composition will change, and with it the Chandrasekhar limit. (This is a bit like the anecdote that prices per square meter will not rise, but will decrease per square meter). Ultimately, the limit beyond which the explosion is, will become less than 1.2 times the mass of the Sun.

And then the most massive white dwarfs, the mass of which exceeds this fatal mark, will lose stability and die in a thermonuclear fire. Such a fate awaits the remnants of about 1% of the stars observed in the universe today. Considering that there are hundreds of billions of luminaries in the Milky Way alone, this will be a truly impressive sight (it is a pity that there will be absolutely no one to enjoy them).

When the universe has nowhere to rush

Okay, but for what reason will the chemical composition of these burnt-out residues change? After all, white dwarfs differ from “living” stars in that thermonuclear reactions that convert some chemical elements into others no longer take place in them.

In fact, the expert reminds, this is not entirely true. Almost no such reactions occur in white dwarfs. It’s just such a small “almost” that no one ever takes it into account.

Strictly speaking, at an arbitrarily low temperature, any two atomic nuclei will sooner or later merge with each other. It’s all about the tunneling effect, sometimes allowing them to overcome mutual electrical repulsion. True, this happens so rarely that it is impossible to register such a process. Any celestial bodies, and even more so the astronomers observing them, will cease to exist before such rare acts of thermonuclear reactions give at least some observable effect.

But we are talking about that stage in the life of the Universe, when everything that can cease to exist will already cease it. There simply will be no forces left in the world that change the fate of white dwarfs faster than this fantastically slow transformation.

Date of the last fireworks

So when will remnants of stars become the last supernovae? According to the calculations of the researcher, in 101100 years.

One followed by 1,100 zeros is not just a big number. This is an incredibly large number. Suffice it to say that in the observable Universe there are about 1080 (one and “only” 80 zeros after it) atoms.

By this time, even black holes have long since evaporated, emanating from Hawking radiation. Therefore, Kaplan calls the explosions of reborn white dwarfs the last interesting event in the universe. After that, it is unlikely that anything will noticeably change in the world.


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