Once-in-a-Lifetime Nova Outburst to Add 'New' Star to Sky This Year

The night sky might be about to gain a brand-new star thanks to a distant sun exploding violently.

This far-distant stellar system is situated around 3,000 light years away from Earth and is usually much too dim to be seen with the naked eye.

This year, however, T Coronae Borealis, or T CrB, is expected to explode for the first time since 1946, briefly shining brighter than the North Star Polaris, according to NASA.

T CrB is a recurring nova, one of only five known to exist in our galaxy. It is actually two stars in a binary system, comprised of a white dwarf and a red giant orbiting each other.

Red giants are stars that have exhausted the hydrogen fuel in their core. The core contracts and heats up while the outer layers expand and cool, causing the star to swell in size and become a red giant. The outer layers of a red giant are cooler, giving them a reddish appearance.

Meanwhile, white dwarfs are the remnants of stars that have exhausted their nuclear fuel and undergone gravitational collapse. They become incredibly dense, typically with masses comparable to the sun but squeezed into a volume roughly the size of Earth.

T CrB goes nova once every century or so as a result of a special property of the white dwarf-red giant system. The white dwarf slowly strips away the atmosphere of the red giant, absorbing hydrogen into itself and getting bigger and hotter. Eventually, it heats up to the point that it undergoes a thermonuclear reaction, exploding in a massive burst of light. This is a nova, which is less powerful than a supernova, as supernovas completely destroy the star.

"The white dwarf is much smaller and much more compact, so you build up a little disc of mostly hydrogen and maybe some helium as well sitting on the white dwarf," Jonathan Blazek, an assistant professor of physics at Northeastern University, said in a statement. "Eventually enough of it builds up and basically ignites. It's not literally burning in the sense of fire; it's thermonuclear burn and you have hydrogen undergoing a fusion reaction."

"Eventually, you build up enough mass on usually the hotter object that it ignites, in this case undergoing fusion, and then suddenly you get a very rapid release of energy so it gets much, much brighter," he said.

After the nova, the white dwarf starts the process over again, repeating this cycle once every 80 years. T CrB last exploded in 1946 and is expected to explode again sometime between February and September 2024.

Usually, T CrB has a magnitude of +10, with a smaller or negative magnitude number meaning an object is brighter. The sun has a magnitude of -27, while the full moon is brightest at -13, and two of the brightest stars in the sky, Sirius and Antares, have magnitudes of −1 and 1, respectively. Objects with magnitudes lower than around +6 are visible to the naked eye.

During the nova, T CrB is expected to jump to a magnitude of +2, becoming a new star visible in the sky. The nova is expected to be visible for a few days with the naked eye and around a week using binoculars before it fades into obscurity once again.

For those hoping to catch a glimpse of the new star, it will be situated in the constellation Corona Borealis or the Northern Crown. The best view will be from a dark area; however, those in cities may also get a chance to see the strange event.

"Obviously, you'll get a better view if you go somewhere dark, but if you go somewhere dark, you'll see a lot of stuff up there," Blazek says. "If you want to have an easier time finding it, stay somewhere bright and then you can only see the really bright stuff, so it'll pop out behind the Boston glow."

Systems like T CrB are of special interest to astrophysicists outside of this strange cosmological phenomenon, as they are also prime for Type 1a supernovae. These are even larger explosions that always appear to have the same brightness. This implies they always happen to stars of around the same mass and are, therefore, crucial to mapping the universe.

"These are cosmologically super interesting because you can see them really, really far away, and because they're almost always the same brightness, you can use them as very particular probes of the universe," Blazek said. "You can basically map out how bright something is at different distances away and use that to say, 'How is the universe changing at different distances?'"

"We're at the stage where we have discovered dark energy using the supernova, but if we want to go to the next level of precision, we need to do a better job of really understanding deep down what these things are, how much variance there is between different objects and things like that," Blazek said.

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