An impression of an artist of a black dwarf, a chilled star remnant that could form in trillions of years
MARK GARLICK / Scientific Source
By Adam Mann
In the unimaginably distant future, cold star remnants, known as black dwarfs, will begin to explode into a spectacular series of supernovae, delivering the ultimate fireworks of all time. That is the conclusion of a new study, which states that the universe will experience one last hurray before everything becomes dark forever.
Astronomers have long pondered the ultimate end of the cosmos. The known laws of physics suggest that by about 10100 (No. 1 followed by 100 zeros) Years from now, mortality will stop, galaxies will darken, and even black holes will evaporate through a process known as Hawking radiation, leaving little more than simple subatomic particles and energy. The expansion of space will almost cool that energy to 0 kelvin, as absolute zero, and signal the hot death of the universe and total entropy.
But while teaching an astrophysics class this spring, theoretical physicist Matt Caplan of Illinois State University realized the fate of one last group of entities that had never been accounted for. After depleting their thermonuclear fuel, low-mass stars like the sun do not pop out in dramatic supernovae; rather, they gradually shed their outer layers, leaving behind a devastating earth-sized nucleus known as a white dwarf.
“They are actually pans that have been removed from the stove,” says Caplan. “They’ll be cool and cool and cool, basically forever.”
White dwarfs’ crushing gravity weight is counterbalanced by a force called depression of electron degeneration. Press electrons together, and the laws of quantum mechanics prevent them from occupying the same state, allowing them to push back and retain the mass of the residue.
The particles in a white dwarf remain trapped in a crystalline grid that radiates trillions of years, much longer than the current age of the universe. But eventually these relics cool down and become a black dwarf.
Because black dwarfs do not have the energy to drive nuclear reactions, not much happens in them. Fusion requires charged atomic nuclei to overcome a powerful electrostatic repulsion and fusion. However, quantum mechanics allows particles to tunnel through energy barriers over long periods of time, which means that fusion can still occur, albeit at very low rates.
When atoms such as silicon and nickel fuse to iron, they produce positrons, the antiparticle of an electron. These positrons would ever destroy some of the electrons in the center of a black dwarf and weaken its degenerative pressure. For stars between about 1.2 and 1.4 times the mass of the sun – about 1% of all stars in the universe today – this attenuation would eventually result in a catastrophic shrinkage of gravity that drives a colossal explosion, similar to the supernovae of higher mass stars, Caplan reported this month in the Monthly announcements from the Royal Astronomical Society.
Caplan says the dramatic detonations around 10 will begin to occur1100 years of now, a number can barely understand the human brain. The already incomprehensible number 10100 is known as a googol, so 101100 would be a year googol googol googol googol googol googol googol googol googol googol googol years. The explosions would continue until 10 p.m.32000 years from now, which requires most of a magazine page to be represented in a similar way.
A time traveler hoping to witness this latest cosmic view would be disappointed. By the beginning of this era, the mysterious substance that acts in contrast to gravity called dark energy, would have driven apart everything in the universe that every individual black dwarf would be surrounded by immense darkness: The supernovae would not even notice each other .
In fact, Caplan showed that the radius of the observable universe would then have grown by about e10 ^ 1100 (where “e” is about 2.72), a figure immensely larger than any of the ones given above. “This is the biggest number I’ll ever have to work with seriously in my career,” he says.
Gregory Laughlin, an astrophysicist at Yale University, praises the research as a fun thought experiment. The value of considering these mind-boggling timescales is that they allow scientists to consider physical processes that do not have enough time to explode in the current era, he says.
However, “I think it’s important to emphasize that all research into the distant future is necessarily tongue – in – cheek,” says Laughlin. “Our view of the very distant future is a reflection of our current understanding, and that view will change from year to year.”
For example, some of the larger unified theories of physics suggest that the proton will eventually decay. This would dissolve Caplan’s black dwarfs long before they would explode. And some cosmological models have hypothesized that the universe could collapse on its own into a large crutch, which precludes the definitive light representation.
Caplan himself enjoys peering into the distant future. “I think our awareness of our own deaths definitely motivates a little bit of fascination for the end of the universe,” he says. “You can always assure yourself that, if things go wrong, it doesn’t matter if entropy is maximized.”
