07/16/2021

Betelgeuse’s False Supernova Alarm

8:15 minutes

This animation combines four real images of the red supergiant star Betelgeuse, the first taken in January 2019 and the others taken in December 2019, January 2020 and March 2020, during the star’s unprecedented dimming. All images, which allow us to resolve the surface of the star, were taken with the SPHERE instrument on ESO’s Very Large Telescope. Credit: ESO/M. Montargès et al./L. Calçada


The famous red giant star, Betelgeuse, sits on the left shoulder of the constellation Orion. It’s one of the brightest stars in the night sky, distinguishable by its faint red hue. 

In December 2019, the star suddenly dimmed to about a third of its usual brightness. Scientists called this the ‘Great Dimming.’ And there was some speculation in the news that the dimming meant Betelgeuse was about to explode in a giant supernova.

four images of a blurred orange dot getting more and more dim with the passage of time, beginning from january 2019 to march 2020
The image on the far left, taken in January 2019, shows Betelgeuse at its normal brightness, while the remaining images, from December 2019, January 2020, and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. Credit: ESO/M. Montargès et al.

But within months, Betelgeuse quietly returned to its original brightness, leaving astronomers perplexed. Now, nearly two years after the initial dimming, a study recently published in Nature proposed a theory for Betelgeuse’s Great Dimming.

Supernova expert Sarafina Nance joins Ira to talk about Betelgeuse, give an outside perspective on the new Nature study, and discuss her science communication work. 


Further Reading

  • Read the paper in Nature.
  • Get more information about Betelgeuse during its dimming from ESO.

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Segment Guests

Sarafina Nance

Sarafina Nance is a PhD candidate in the Department of Astronomy at the University of California, Berkeley & Lawrence Berkeley National Lab in Berkeley, California.

Segment Transcript

IRA FLATOW: I’m really looking forward to our next story because it talks about my favorite constellation Orion. Orion is very easy to pick out in the sky and it has a star in the upper left part that you can actually see with your naked eye. That it has a faint red color. That’s the famous red giant star Betelgeuse. One of the brightest stars in the night sky. Something strange happened to its reddishness.

In December 2019, the star suddenly dimmed to only one third its usual brightness. It came to be called the Great Dimming. And there was some speculation that the dimming meant Betelgeuse was about to go supernova kaboom. But within months, Betelgeuse quickly returned to its original brightness, leaving astronomers perplexed. And now nearly two years after the initial dimming, a study recently published in Nature proposed a theory for Betelgeuse’s strange behavior.

Sarafina Nance is a PhD candidate in the Department of Astronomy at the University of California at Berkeley and the Lawrence Berkeley National Lab. And while she is an astrophysicist and a supernova connoisseur, she was not the author on the Nature study but is here to talk about it. Welcome Sarafina.

SARAFINA NANCE: Thank you so much for having me. I’m so excited to be here.

IRA FLATOW: Did you follow it when it first started dimming back then?

SARAFINA NANCE: I did. Yeah. In part because I could see it with my naked eye. I would walk outside at night that I would stare up there and be like, oh my God, what’s happening to my star? So it was very exciting.

IRA FLATOW: This was so you call it a rare event then. I mean, it’s not something you would see all the time. Is it meaningful? What happened do we know what happened to it?

SARAFINA NANCE: Yeah, I think we are working hard to figure that out. And it seems like there’s some consensus now on what exactly happened. But it was an interesting sort of progression of trying to understand what’s going on within the star and what that means for other red supergiants could this great dimming happen in other places around our universe? So it seems like we think that dust is the ultimate culprit. And in astronomy that’s actually pretty common and somewhat sad.

But also exciting for those who study dust. So we think dust actually probably obscured the star from our line of sight. Meaning we saw the star appear dimmer than it actually is. This new study also proposed that it seems like there could have also been a sort of cooling on one part of the star. A cooling that made the light appear dimmer. And so those two factors sort of came together to make the star appear, as you said, about 35% as bright as it normally is.

IRA FLATOW: So is that the consensus now of what happened?

SARAFINA NANCE: I think so. Yes. Yeah. It seems like it’s dust with some cool convection and temperature changes as well.

IRA FLATOW: This is Science Friday from WNYC Studios. So why are we so interested in studying it to see what happened?

SARAFINA NANCE: Well I think Betelgeuse is a really fascinating star for a lot of reasons. One of which we already talked about. We can see it. And also because it is a very large red supergiant. Very close to us. About 724 light years away. And so when it explodes as a supernova, we will be able to see it from Earth. And so it’s exciting to try to understand what’s going on within the star and to see how long it has before it explodes so that maybe we can try to catch that.

IRA FLATOW: I know that seeing a supernova, seeing a star explode, is a really rare event too. Are you kind of disappointed it was not a supernova?

SARAFINA NANCE: I’m a little sad. I’m a little– I didn’t have too high hopes, but I’m a little bummed.

IRA FLATOW: Yeah. What can you learn by studying supernovas? Why are we excited about them?

SARAFINA NANCE: I can gush about this for hours or days. Supernova are some of the most interesting exotic parts of our universe. They eject elements into their surroundings that actually form the basis of most matter in our universe, including us. You know, when Carl Sagan said we are star stuff, we are. We are the stuff of stars thanks to supernova.

So that’s one reason. Another reason is there just some really fascinating physics that goes on in a star before it explodes. And we get to use supernova as laboratories for some of the most interesting and complicated explosion physics that exists. And finally, supernova have really cool applications.

I am currently using core collapse supernova, so really big stars that explode at the ends of their lives, just like Betelgeuse will, to try to measure the expansion rate of our universe. So we know the universe is expanding. We know that expansion rate is accelerating with time. And we can use supernova to try to understand exactly how fast it’s expanding and how that changes with time.

IRA FLATOW: You know, there was a lot of hype about this in social media and wherever because people really love that star. And they were wondering what could happen to it. Do you think that serves a purpose? The hype that at least gets the public talking about astronomy?

SARAFINA NANCE: I think that this is why science communication is so important. I think that getting people interested, engaged, excited, passionate about looking up out at the night sky and thinking about what’s out there is incredibly important.

IRA FLATOW: I notice that you’re very active in social media. Do you think social media has a special place as opposed to traditional forms of media for being a science communicator?

SARAFINA NANCE: I do. I think that social media has its pros and cons. But in some ways, how often do you get access to the best scientists in the world, to some of the people making the most interesting discoveries, and you get to ask them questions. You get to interact with them. And that’s totally new. That hasn’t been done before, social media. And so to me that means that we can increase the representation of people who are communicating science.

And who are actually elevated in sharing their work and sharing their discoveries. And that increasing representation is incredibly important when you want to prioritize different voices, marginalized voices, and allowing people to see that there are many different types of scientists and anybody can be a scientist.

IRA FLATOW: That’s really interesting. You say that now. You write on your website that as an Arab woman in the sciences, I also hope to change the narrative of who can be a scientist and what a scientist looks like.

SARAFINA NANCE: Yeah, I think for most of my life, I didn’t feel like I had a place in astronomy. And a lot of that is from explicit and implicit messages that I got very early on. I had a male astronomer tell me when I was about nine years old that I could not become an astronomer when I grow up. And–

IRA FLATOW: Really?

SARAFINA NANCE: Yes. And that sticks with you. I remember that moment very vividly. And that has continued throughout most of my career in various capacities. But on the other hand, I’ve had some amazing mentors who have helped me and a community of people who have helped me pursue my dreams. And so my hope is to be the woman be the scientist that young Sarafina would have wanted to look up to when she was a young girl. And be that person for anybody who’s interested in and pursuing their dreams.

IRA FLATOW: Well we wish you all the best of luck. And as one person famously said many years ago, keep looking up.

SARAFINA NANCE: Keep looking up. Thank you so much for having me.

IRA FLATOW: Thank you for taking time to be with us today. Sarafina Nance, PhD candidate in the Department of Astronomy at the University of California at Berkeley and Lawrence Berkeley National Lab.

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Ira Flatow is the host and executive producer of Science FridayHis green thumb has revived many an office plant at death’s door.

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