Podcster: Rob Sparks; Guest: Dr. Steve Howell
Title: A Stellar Companion For Betelgeuse
Organization: NOIRLab
Links: https://www.facebook.com/NOIRLabAstro ; https://www.instagram.com/noirlabastro/ ; https://www.youtube.com/noirlabastro ; @NOIRLabAstro
NOIRLab Press Release: https://noirlab.edu/public/news/noirlab2523/; https://iopscience.iop.org/article/10.3847/2041-8213/adeaaf; https://www.nasa.gov/science-research/astrophysics/nasa-scientist-finds-predicted-companion-star-to-betelgeuse/; https://noirlab.edu/public/news/noirlab2523/; https://www.nytimes.com/2025/07/21/science/betelgeuse-star-companion.html
Description: Astronomers have discovered a companion star in an incredibly tight orbit around Betelgeuse using the NASA and U.S. National Science Foundation-funded ‘Alopeke instrument on Gemini North, one half of the International Gemini Observatory, partly funded by the NSF and operated by NSF NOIRLab. In this podcast, Steve Howell describes the discovery of this long sought after companion and future observations research into this type of star system.
Bio: Rob Sparks is in the Communications, Education and Engagement group at NSF’s NOIRLab in Tucson, Arizona
Dr. Steve Howell has spent over 40 years as a professional astronomer. During that time, he developed digital (CCD) imaging instrumentation and data reduction techniques space and ground-based telescopes, performed research in a wide variety of astronomical areas and collaborated with hundreds of astronomers world-wide. His areas of expertise are instrumentation, interacting binaries, stellar evolution, and exoplanets. Howell’s professional work has providing community service to the field of astronomy as well as formal and informal STEM education.
Transcript:
[Rob Sparks]
It’s the 365 Days of Astronomy podcast, coming in three, two, one. Hi, this is Rob Sparks of NSF Moore Lab. Welcome to this episode of the 365 Days of Astronomy podcast.
My guest today is a longtime friend, Steve Howell from NASA Ames Research Center. Good morning, Steve. How are you doing today?
[Dr. Steve Howell]
Good morning, Rob. I’m doing well. It’s another great day here in the Bay Area.
[Rob Sparks]
Yeah, a little hot here in Tucson this time of year, so I wish I was there. Anyway, first, could you tell us a little about yourself and your career and research interests?
[Dr. Steve Howell]
Sure. So I’ve been doing astronomy for about 40 years now. I just flew by, I guess.
My research interests have varied over time to basically look at, can I build an instrument that’ll do something that nobody’s done before? And so I’ve been pretty successful at finding ways to build instruments to make observations of stars and galaxies and quasars and whatever that haven’t been done before. And I think we’re going to talk about one of those today.
[Rob Sparks]
Yes, we are. You’ve been on this several times to meet always about interesting things that have never been done before. So that definitely fits with what you do.
We’re going to talk about Betelgeuse today. It’s long been thought that Betelgeuse had a companion star. And I thought, why did astronomers think it might have a companion star?
And what inspired you to take up the search for this potential companion?
[Dr. Steve Howell]
Yeah, so Betelgeuse is a fantastic star. As we all know, if you’ve ever looked at the night sky, it’s hard to miss Betelgeuse. It’s this spectacularly bright red star in the constellation of Orion, where all the other stars are nice and blue.
So it’s really a great target. You can see with your eye quite well, it’s very bright. So for maybe 100 years or more, there’s been suspicions that something else is going on with Betelgeuse besides its regular variations.
It’s a red supergiant. It’s a very large star. If you put it at the center of our solar system, its outer atmosphere would extend almost to the asteroid belt.
So it’s much, much bigger than our sun. And so the star pulsates. This is what stars of that kind do.
It pulsates with a period of about 600 days, I think it is. I’m sorry, 400 days. But for a long time, there’s been a period of about six years that people have noticed in the data.
And they never knew what to attribute that to. And there’s been studies done for, as I say, almost 100 years trying to figure out what this extra period is. In the fall of 2024, two very large, detailed, complete studies, independent studies, looked at 100 years of data for Betelgeuse.
And they each came to the same conclusion. Betelgeuse definitely has a companion. They predicted its orbit, they predicted its position, and they predicted its separation.
But they said, it’s so close to Betelgeuse, and it’s so much fainter than Betelgeuse, no one will ever be able to see it. So that was one of the challenges that I took up. And I guess we’re here to talk about that it worked.
[Rob Sparks]
Yeah. So let’s talk about how you went about this too. That totally fits with your MO.
Have a challenge and go for it, right? Yeah. So what instruments, telescopes, and observations used to make this extremely challenging observation in this very challenging search?
Right.
[Dr. Steve Howell]
So the two big challenges, and Rob, you’re well aware of one of these, is Betelgeuse is incredibly bright. If you look at Betelgeuse with any telescope, basically, with any kind of a camera, it saturates your camera. Betelgeuse is such a bright star.
And I was attempting to observe Betelgeuse with the Gemini 8-meter telescope. So we’re looking at a star as bright as Betelgeuse with an 8-meter telescope. So that sounds crazy.
Why would you do that? The reason is that the other thing you need to do, besides looking directly at a very bright star, is to find this companion, you had to have very high resolution. You had to separate this tiny, faint companion from the star Betelgeuse.
And the way you can get lots of resolution is to get a larger and larger and larger telescope. That gives you better angular resolution. So Gemini was the ideal telescope to try this with.
I just had to overcome the fact that Betelgeuse is very bright. And it turns out that we have an instrument we built that’s on Gemini, Gemini North on Mauna Kea. And that instrument allows us to take incredibly short exposures.
So we observed Betelgeuse in the blue part of the optical spectrum. Yes, it’s a very red star. So we observed it in the blue because it’s slightly less bright in the blue.
And we took thousands of exposures. Each one was 14 milliseconds in length. And that’s a way we could not saturate our detectors.
All these data were processed with this software pipeline we used to reduce our data. And we made a very high resolution image of Betelgeuse. And sure enough, right where it was predicted, there was the companion star.
[Rob Sparks]
Well, great. So that verifies the prediction. That helps a lot, doesn’t it?
It does indeed, yeah. So tell us about this companion you discovered. And what did you learn about this companion from these observations, other than where it’s supposed to be?
[Dr. Steve Howell]
Right, it’s right where it’s supposed to be. So the companion, we talked just briefly here before that Betelgeuse would be about the size of the asteroid belt in our solar system. The companion orbits about at the size of, or about at the distance of the asteroid belt in our solar system.
So the companion is actually orbiting inside the very large extended atmosphere of the star Betelgeuse. It’s about one and a half times the mass of the sun. It probably has not yet even formed as a real star yet.
Betelgeuse is a pretty young star, young in astronomy. It’s only 10 million years old. So that’s pretty young in astronomy.
And the companion and Betelgeuse were, of course, both formed together as a binary star. So at one and a half solar masses for the companion, it hasn’t even reached the main sequence yet. So it’s still a forming star, but now it’s inside the atmosphere of Betelgeuse, since Betelgeuse has become a red supergiant.
And that doesn’t really bode well for the future of that star. So what does it hold for the future of that star? Well, that star, because it’s inside this very tenuous atmosphere, but it’s still inside an atmosphere, it will have drag, orbital drag.
And so it will slowly spiral in to Betelgeuse. The prediction is within about the next 10,000 years. Oh, wow.
[Rob Sparks]
So it’ll literally be eaten up by Betelgeuse. Right. Yeah.
So what are the next steps for learning more about Betelgeuse companion? And are there other similar systems you might be exploring in the future as well? Yeah.
[Dr. Steve Howell]
So that’s a great question. So we and many others are going to look at Betelgeuse a lot more, of course. We now know there’s a companion there.
We want to understand the companion in more detail. As I mentioned, we only had one measurement of it at one wavelength, a very blue wavelength. So the next chance we have to observe this companion being somewhat widely separated from Betelgeuse will be in the fall of 2027.
So we have a few years to think about our planned observations. Of course, at this time, the star should be on the other side of Betelgeuse. It should have orbited halfway around Betelgeuse.
We’ll see it on the other side. But we would like to get more observations, not only in wavelengths of optical light, but perhaps in wavelengths of other light as well. We also have noted that a number of stars like Betelgeuse, Antares, for example, also a red supergiant.
Also very easy to see. Also very easy to see, that’s right. It also shows one of these very long extra periods of about six or seven years and has also been thought that it has a companion as well.
So our plan is to observe stars like Antares and a few other red supergiants that seem like they might all have companions. The problem with Antares, much like with Betelgeuse, is we have to wait for the companion, the predicted companion for Antares, to be at its widest separation. So we have a chance of separating the two stars.
And it turns out that is in July of 2027.
[Rob Sparks]
So 2027 will be a fun year. Yeah, it’s going to be a busy year for you. Well, thank you for joining me today, Steve.
That’s great. This is a very interesting topic. And I know there’s a lot of people, very famous stars, so a lot of people have a great interest in it.
[Dr. Steve Howell]
Great. Well, thanks, Rob. It’s always fun to chat with you.
And yeah, let’s all look at Betelgeuse. Someday it will explode as a supergiant.
[Rob Sparks]
Yeah, and hopefully not in the next 10,000 years, it’ll take that little star with it. Yes, it will. Thanks, Steve.
This is Rob Tegar signing off for this episode of 365 Days of Astronomy podcast. You are listening to the 365 Days of Astronomy podcast. Cool.
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365 Days of Astronomy
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