Exploding Black Dwarfs Could Be the ‘Last Interesting Thing to Happen in the Universe’ – Gizmodo UK

This is the way the world ends, said T. S. Eliot in his famous poem, Not with a bang buta whimper. These days, scientists considerthe heat-death of the universe to bethe whimper, buta new theoretical analysis predicts thatthe cosmos will breathe its final gasp in the form of exploding black dwarfs.

Trillions upon trillions of years from now,long after the last stars have fizzled out, the heaviest black dwarfs will start to go supernova, according to newresearchpublished in Monthly Notices of the Royal Astronomical Society. Black dwarfs are the frozen remnants of white dwarfs, which themselves are theremnants of low-mass stars. The sole author of the study, astrophysicist Matt Caplan from Illinois State University, says these explosions will be the last interesting thing to happen in the universe, as heexplainedin an ISUpress release.

The universe could end inany number of ways, but the current best guess is that itll continue to expand long after everything inside it has been torn to shreds, including galaxies, solar systems, stars, and even atoms. By the time black dwarfs are set to pop, the universe will be cold and lifeless,Caplan wrotein an email to me.

The expansion of the universe will have long since separated all remaining objects by distances so enormous that no light will ever be able to reach from one to another, he said. Every object will find itself in a universe completely devoid of anything else in every direction. It will be cold and near absolute zero.

When extant stars go supernova, its on account of excess iron in their coresthe result of internal nuclear reactions. The same cannot be said for smaller stars, which eventually burn out and shrink into white dwarfs. According to theory, white dwarfs will eventually lose their lustre and freeze in the far future, transitioning into black dwarfs.

Without a heat source,they simply cool off for all eternity, until they turn black and no longer shine, saidCaplan. Its a bit like taking a hot skillet off the oven all it can do is cool.

These hypothetical objects would be roughly the size of Earthbut with masses approaching that of our Sun. Importantly, nuclear reactions will still occur inside these dense, frozen worlds, but at appreciably slower rates than normal. And as the new study predicts, these reactions will result in a steady buildup of iron, though at cosmologically vast timescales. With this in mind, Caplan crunched the numbers to estimate how long it will take for these black dwarfs to produce enough iron to trigger a supernova explosion.

The answer, at 101,100years, is hilariously long, said Caplan. The age of the universe itself is closer to1010years, so if you were to try to write out 101,100it would have 1,100 zeros and take up most of a paragraph, he explained. Or as Caplan put it in the ISUrelease, its like saying the word trillion almost a hundred times.

Importantly, these explosions will only happen among the largest of the black dwarfs, namely those around 1.2 to 1.4 times the mass of the Sun. These supernovaethe last to ever happen in the universe will eventually stop around 1032,000years from now, after which time the cosmos will truly be a quiet and uneventful place.

Caplan said his analysis took the effects of an expanding universe into account. However, if dark energy is different than we currently suspect,then the expansion of the universe could destroy the black dwarfs long before they have a chance to explode, he said. Whats more, Caplans calculations were based on our current understanding of nuclear physics, astrophysics, and cosmology, but to be fair, scientists cant be certain if the laws of physics and the universal constants will remain the same in the far future. Itspossible, for example, that the universe wont even exist at this future juncture.

Some theories of particle physics predict that the proton is fundamentally unstable and will decay away, though this has yet to be observed or confirmed. If thats the case, then all matter will sort of evaporate long before any black dwarfs explode, said Caplan. Thats just one example. In a sense, our understanding of the far future is entirely dependent on our understanding of the laws of physics today, and small changes in physics as we know it can have enormous consequences for the final fate of the universe and its contents.

Though Caplan said these black dwarf supernovae will be the last interesting thing to happen in the universe,we asked him if something of consequence or interest might happen after this phase.

Depends on your definition of interesting, he said. If a cold iron ball floating in a universe where it is completely causally separated from all other objects is interesting, then I suppose you could find something of interest.

Okay, fair point. But if theres any consolation in all of this, its that the universe will continue to expand forever, at least according to some theories. Itll be dead, cold, and lifeless, but at least itll still be around.

Featured image:NASA / JPL-Caltech

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Exploding Black Dwarfs Could Be the 'Last Interesting Thing to Happen in the Universe' - Gizmodo UK

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