There’s a chance we could see a white dwarf star explosion this year.
T Coronae Borealis, a binary star system and recurrent nova located roughly 3,000 light-years from Earth, is expected to erupt sometime in 2025.
According to Dr. Phil Langill, Director of the Rothney Astrophysical Observatory and Associate Professor of Physics and Astronomy at the University of Calgary, a recurrent nova is very different from a regular supernova.
“A supernova is a one-time event for a star. It’s a dramatic end to its life, and it gets completely destroyed in the explosion,” Langill explains. “It’s one of the most energetic and luminous events that Mother Nature builds in the whole universe. A recurrent nova is slightly different.”
A recurrent nova occurs in a binary star system where one of the stars has aged into a white dwarf.
Unlike our sun, a fluffy ball of gas, a white dwarf is small, dense, and solid.
They are very small, very hard, and as Dr. Langill explains, they have an actual surface that could be stood on.
"So, it's weird that it's even called a star. But, they are dots of light in the sky, and they look like a star to the naked eye."
This white dwarf star is in close enough orbit around another star that it pulls and steals material and gas off of its neighbouring star, which then gets deposited onto the surface of the white dwarf star.
"And it's a very hostile environment. And when enough material piles up, then you can trigger a nuclear explosion. It's like a ticking time bomb," Langill says. "The material transfers over slowly over many, many years, and when it gets thick enough on the white dwarf star, the temperatures and pressures that are created are so high that suddenly this hydrogen gas can undergo a nuclear explosion and you get hydrogen burning into helium."
This explosion doesn't destroy the white dwarf star, nor does it destroy its companion star.
When it does explode, a new star will be visible in the night sky.
"So, these things get super bright and super energetic, and they can happen repeatedly. That's why they're called recurrent nova."
These recurrent novas are not as energetic as a supernova, but the process of stealing gas and material from its companion star gets repeated after each explosion.
The T Coronae Borealis recurrent nova has been known for some time, and according to Langill, there seems to be a pattern to when it explodes.
"But, it's a very complex environment, and you never know exactly when the next explosion is going to happen. The rumor was going around last year, in the fall, that stay tuned, this thing's going to blow, because predictions are showing that. But, of course, Mother Nature tricks us all the time. And so, it's a year later, and we're still waiting."
Langill adds that hopefully it will happen sometime before Christmas.
Langill says that this binary star system is strange, because between the giant explosions, the brightness of the star system increases and decreases.
"People with their telescopes can notice there's this variation going on. It doesn't get bright. You know, it's not a particularly bright star, so you need to study this thing very carefully with instruments, but you can see that its brightness is not constant."
So, if this recurrent nova does explode this year, where in the sky will it be seen?
"Let's start with the Big Dipper. Everybody knows where the Big Dipper is. The Big Dipper has a handle that's filled with bright stars that point the way to another bright star called Arcturus," Langill explains. "So, what I think in my little brain is, I look at the Big Dipper, I see the handle of the Big Dipper, and I follow the arc defined by the shape or the path of the stars in the handle of the Big Dipper."
If you follow that arc, they point almost directly to a very bright star, one of the brightest stars in the sky, called Arcturus, which has a bit of a reddish colour on a dark night.
Arcturus is in the Boötes constellation.
From there, if you look to the left, the Corona Borealis constellation is sitting right there, snuggled between Boötes and Hercules.
Corona Borealis is commonly referred to as the Northern Crown, with T Corona Borealis perched on the left-hand side, like a little jewel in the crown.
Currently, T Corona Borealis can just barely be seen by the naked eye, but when it explodes, Langill says it will become much brighter.
"Strangely bright in the sky, where you were hardly able to see this star with your naked eye before. It will be, dare I say, rivalling Arcturus in how bright it could potentially be. Maybe not quite as Arcturus, but you won't need binoculars to spot it anymore. Once it goes, you'll be able to spot it with your eye, no problem."
Dr. Langill says it happens pretty suddenly, making it difficult to predict.
"Let's say there's an earthquake coming. You know, there's been a lot of little eruptions happening, and people are thinking, 'Oh, the big one's coming.' Would they be able to tell when the big one's coming? You know, there are clues, right? But, being able to nail it down exactly is hard to do."
With that said, he added that the experts have high-powered instruments, which might get clues a couple of days or maybe a week before it will explode.
Langill says that the Rothney Observatory is going to try and use a spectrograph (an instrument used to split light into different colours) to see a lot more detail of the explosion.
"I'd really like to capture the spectrum transition from regular binary star to the explosion, because there's so much good physics that you can learn about by looking at the spectra."
T Corona Borealis is roughly 2,700 light years away, meaning that when the explosion becomes obvious to our eyes here on Earth, the explosion actually happened almost 3,000 years ago.
An explosion that far away that's visible from Earth would have happened around the year 675 B.C.
According to Dr. Langill, this recurrent nova explodes roughly every 80 years, with the last one erupting in 1946.
While T Corona Borealis explodes every 80 years or so, these explosions don't cause much damage.
"Even though the explosion creates some gargantuan amount of energy, the system survives. The companion star doesn't get blasted into oblivion, the white dwarf star itself hardly gets altered at all."
Though the cycle is self-repeating, it does eventually come to an end.
When the mass of the white dwarf star gets too big, the self-gravity becomes too much to bear.
"One of the types of supernova explosions is when a white dwarf star collapses under its own gravity. And it's called a type one supernova, and gravity completely destroys the star."
Once a star goes supernova, it can lead to things called neutron stars, which are cousins to black holes, and are the densest material in the observable universe.
"We are pretty sure that black holes can also be formed in a supernova blast," says Langill.
What would happen if our sun went supernova?
Dr. Langill says the sun won't go supernova, but will die eventually.
"It would be like a Hollywood horror movie, for sure."
But, according to Dr. Langill, the sun won't die for another five billion years.