Astronomers say we might be on the verge of a once-in-a-lifetime opportunity. They predict a star about 3,000 lightyears from Earth in the constellation Corona Borealis that cannot normally be seen with the naked eye is about to go nova. That would make it temporarily as bright as Polaris, also known as the North Star.
Joining me now to talk more about it is Daniel Caton. He is an astronomy professor at Appalachian State University.
Marshall Terry: So give me an idea of where in the sky this star, called T. Corona Borealis, is located.
Daniel Caton: So Corona Borealis is the northern crown, and it's a little arc of several stars, and it turns out that this time of the year, it's right overhead as it gets dark, between, say, 9 and 10 [p.m.], it's really very near our zenith. It would be easy to find second magnitude stars, you might need to get out of the light pollution of Charlotte to a little bit darker location; maybe in the suburbs, you can see it. To give you an idea, the star itself, when at nova, is expected to get to about second magnitude, and that's about the brightness of most of the stars in the Big Dipper, which is also up in the northwest.
Terry: So what is a nova, exactly? I’ve heard of a supernova where a star is destroyed. This is different?
Caton: Right. Well, it is different, but maybe related and we're not quite sure. So a nova is when you have a pair of stars orbiting each other, and about half of all stars, unlike our Sun, are found to be orbiting a companion star, and one star has evolved to where it's shed off its outer layers and it's out of fuel. And what's left is a white dwarf, which is a about 10,000-degree surface core of that original star and it's about the size of the Earth, so that's all that's left. But it's a whole solar mass of material in that. And this, in fact, by the way, is the fate of our Sun, and his companion is, in this case, a red giant, a star that is also now evolving. And so it's starting to expand to where some of the gas in this atmosphere bleeds over, falls over onto the white dwarf, and so this can go on for a while, in this case, about 80 years. And then finally, you have too much hydrogen fresh fuel on the surface of this white dwarf and the temperatures and pressures reach the point where there's a nuclear explosion and H-bomb goes off over the whole surface. It doesn't destroy the star, but it's a tremendously brighter star after that happens.
Terry: You mentioned it can take about 80 years. This has happened before with is particular star. The last time was in the 1940s, right?
Caton: 1946 and prior to that,1866. So it's something that repeats pretty regularly around 79 years. So the current prediction is it should happen again in the year 2025, ± 1.3 years. So we're sort of in the window, but there are also signs of its current behavior that are indicating that it's getting ready to go.
Terry: How common are these recurring novas in our Milky Way galaxy?
Caton: There's not a whole lot, I think, total there may be 100 or so. There's about 10 that we're keeping track of, so we only have a couple of handful of stars to even model this behavior on. So that there's only a handful or so then that have been observed to repeat a couple of times.
Terry: And we're talking about this like it's going to happen, but given how long light takes to travel, this actually happened thousands of years ago. Am I thinking of that in the right way?
Caton: Yeah, but, you know, 3000 years ago, but it’s moot. I mean, that's just automatically built into everything we observe. We observe galaxies that are billions of light years away, and we're looking at them as they were billions of years ago. And that's just the way it is, so we don't really think much about that.
Terry: So when exactly is this nova expected to occur in a way that we can see it and what should people do if they do want to see it?
Caton: Well, we don't exactly know, but what happens particularly with T Cor Bor (T. Corona Borealis) that's been observed since the 1800s, and we've seen two outbursts, nicely spaced and with a good measurement of the brightness through the whole period between those bursts, by a whole bunch of astronomers, including a lot of hobbyists, amateur astronomers who observe it. We know that between outbursts, it's pretty much static in its brightness for a long time. Then it rises about half the magnitude or more and reaches this plateau. It's already there, and then, in the past, it drops off that plateau and then comes back to its quiescent brightness and then bursts. And we are right on that decline from the plateau. So it could be tomorrow, it could be tonight, it could be next month, it could be next year. Well, we can't exactly tell, but it's being observed by hundreds of amateurs and others around the planet on an average of about once every 12 minutes. All the time, someone on the planet is observing it. So we're going to have a good handle on when it really starts to go up.
Terry: And when it does, as you said earlier, people should just look up and literally straight up because it’s kind of straight over our heads?
Caton: Yeah, Corona Borealis is right overhead. It's kind of near a star called Arcturus, a bright orangish star, a giant of its own. You can find Arcturus by following the arc of the handle of the Big Dipper, then you follow the arc to Arcturus. And it's within 10 or 15 degrees of Arcturus, so you'll see this little arc of stars near the crown.
