New star in Puna sky?

[terracore]

From spaceweather.com

"THAT NOVA YOU'VE HEARD ABOUT IS ABOUT TO EXPLODE: By the time you finish reading this story, there could be a new star in the night sky. Recurrent nova T CrB (pronounced "tee-core-bore") is poised on the knife edge of a once-in-a-lifetime explosion.

"Our best estimate for the time of eruption is close to now," says Brad Schaefer, Professor Emeritus of Astronomy at Louisiana State University.

Schaefer is a leading expert on T CrB. He's been studying the star since he was a teenager. "When I was 18 year old, I calculated when T CrB should erupt again, and I've been waiting for this moment ever since," he says.
T CrB is a "recurrent nova." That means it erupts not just once, but over and over again. Its explosion in 1866 was the first nova astronomers had ever seen in detail. "No one knew what caused it," says Schaefer. Another blast in 1946 established its period (79 or 80 years) and led researchers to the modern interpretation:

Located 3000 light years away, T CrB is a binary star system consisting of an ancient red giant circled by a hot white dwarf. Hydrogen from the red giant spills onto the surface of the white dwarf. It takes about 80 years to accumulate a critical mass, then--BOOM--a thermonuclear explosion occurs. "It's an H-bomb that blows up on an incredibly large scale," says Schaefer.

After an explosion, the process resets and repeats. Looking at old light curves, Schaefer realized that T CrB tells us when it's about to explode. Approximately 1.1 years before each blow-up, there's a "pre-eruption dip" in brightness. Amateur astronomers working with the American Association of Variable Star Observers (AAVSO) detected the pre-eruption dip in March 2023:

Above: The pre-eruption dip in March 2023

"If the star behaves in 2023-2024 as it did in 1945-1946, then the next eruption should take place in 2024.4+-0.3," says Schaefer. "That's May 2024 plus or minus a few months."

The explosion will be visible to the naked eye. Schaefer expects it to be about as bright as the North Star (2nd magnitude). When it blows, T CrB will burst forth as an extra jewel in the "Northern Crown" (the constellation Corona Borealis), easy to find high in the summer night sky between Hercules and Bootes.

"T CrB will be the brightest nova for generations," says Schaefer. "It's a chance for everyone in the world to step outside, look up, and see the hellfire."

Observing tips: (1) Tonight, go outside and see what Corona Borealis normally looks like: sky map. Then, when the nova explodes, you'll be able to tell the difference. (2) Sign up for Space Weather Alerts. All subscribers (Basic and Pro) will receive an immediate text message when the nova explodes."


If anybody has any Puna specific viewing tips, would appreciate reading them.

[TomK]

You can now observe it from sunset to around 1 am in the NE. It sets at around 2 am, but you'll have a hard time seeing it after 1 am. It's too faint to be seen by the naked eye but when it goes nova it should be visible. I have to take issue with this:

"The explosion will be visible to the naked eye. Schaefer expects it to be about as bright as the North Star (2nd magnitude). When it blows, T CrB will burst forth as an extra jewel in the "Northern Crown" (the constellation Corona Borealis), easy to find high in the summer night sky between Hercules and Bootes.

"T CrB will be the brightest nova for generations," says Schaefer. "It's a chance for everyone in the world to step outside, look up, and see the hellfire."

It will surely be hellfire if you lived in that system when the nova occurs, but from our position, it's going to look like a normal star. Unless something unexpected happens, it'll be about as bright as the pole star, as mentioned, and that's about it. Scientifically, it will be very interesting, but for the casual observer, I don't think it'll make headline news anywhere.

PS. If anyone is interested in the science behind novae and why recurrent novae are predictable, I'll be happy to explain if you don't want to look it up yourself. Just ask.

[kalianna]

Ah, TomK, I think you underestimate the mediaʻs ability to turn almost anything into an "awesome" or "stunning" or "once in a lifetime" event. Theyʻve been promoting this for weeks already. Hereʻs a couple of prime examples from our internetʻs always reliable click-bait sources:

"NASA: Nova Explosion to Be ‘Once-in-Lifetime’ Event in Night Sky" https://learningenglish.voanews.com/a/na...64089.html

"Nova explosion of nearby star will soon light up Earth's skies" https://www.earth.com/news/t-coronae-bor...ths-skies/

etc. Having never recovered from my broken heart after waiting my whole life to see the magnificent Haleyʻs comet, I donʻt get too excited about this stuff any more. And after seeing you compare it to the north star, which is rarely visible in Punaʻs cloudy evening skies and even when clear takes a bit to find, Iʻll check it out during this relatively dry spell and let you know if my life was changed by this event. Thanks for the reality check.

[TomK]

There's a difference here. Predicting the brightness of comets is very hard; it's impossible right now. We can certainly predict their orbits to the second, but predicting how bright they'll be involves so many variables we don't know. I understand the media has become involved, and predicting when a recurrent nova will occur is easy. In this case, the media are quoting a so-called expert, and even the expert says it won't be brighter than 2nd mag, which is not something that will stand out in the night sky. That would be fine, but the media quotes him as saying we can see the hellfire. Well, we can, but it'll just look like another star. Some might get excited about it, but I don't, other than it's something scientifically interesting.

[TomK]

There's a decent article in Sky & Telescope about the potential nova:

https://skyandtelescope.org/astronomy-ne...t-to-know/

I would caution those expecting it to become as bright as the pole star, which isn't very bright, and the nova's brightness depends significantly on the event's geometry. As material falls from the red giant, it's located in one spot. That spot will keep changing as the stars orbit each other, but it is the point where the mass will become critical. If that point is on the far side of the white dwarf, we won't even see a magnitude 2 star; it will be much fainter.