Short Wave - Why scientists are stoked about mysterious black hole stars

Episode Date: August 21, 2026

You've heard of black holes. You've heard of stars. But have you heard of the newly discovered black hole stars that may explain multiple mysteries of the universe? We just did and we're honestly freaking out about it. Learn everything you need to know about it in this episode. Plus, hear some other cool stories fresh off the presses: Which exercise can help reduce your risk of dementia and how shrews shrink — and then regrow — parts of their body throughout the year.Interested in hearing more reporting on space, scientific mysteries or other emerging science? We want to know! Email us what you'd like us to talk about at [e-mail]!Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

Hey, Regina Barber here. To ask if you're following Shortwave on the NPR app or whichever one you're using, it's a little action that goes a long way for our small team. Okay, here's the show. You're listening to Shortwave from NPR. Shortwavers, Nate Rot here with my co-host, Gina B. Hey, Nate. We are back with our biweekly science news roundup with Friend of the Pod

and host of all things considered Elsa Chang. Are I really a friend? Thank you. Oh, Elsa, your family. Okay, so our first topic is in Gina's wheelhouse, Elsa. Space. Of course. The whole universe is my wheelhouse.

Yeah. And it's a wild mystery that we're going to be talking about that's being described as a brand new object, a black hole star. A black hole star, I don't even know what that is. Well, Elsa, to warm up for this discussion about the regular black holes of our universe, we are going to quiz you. Oh my God, no, I'm already nervous. What's happening? On some black hole facts that Shortwave has covered in the past, so there's no excuses for you here.

Oh, my God, I haven't committed everything that comes out of your mouth, my memory. Lock in. Okay, first question. Black holes are not actually holes at all. What shape are they? Triangle. Sadly, no. That's not correct.

Black holes are spheres that are kind of squished. It's like three-dimensional. There's spheres. I'd like to know if spheres, one syllable or two-syllables, that's my conundrum. Spheres. I don't have an answer to that either. Second question. If you were to fall into a black hole, Elsa, depending on the black hole, your body could be stretched like a noodle.

Ow. Scientists have a name for when that happens. What is it? Making pasta? The clue is like a noodle. It's like a noodle. Canoodling? I like that.

No, space is not that romantic. It is spaghettification. I swear to God, I was about to say nudification. So I was like almost there. You're so close. It doesn't actually sound fun. And another weird thing happens, your perception of time and space flips. So, you know, time gets really weird.

Okay, what's my last opportunity for humiliation? You're going to get this one. Do we or don't we, in part, owe our existence to a black hole? I guess we do? Correct. Correct, Elsa. See, you did it. So the black hole that's at the center of our galaxy, the Milky Way also helped it form.

Astronomers don't know exactly how that works, but we all have ideas. All right, Elsa. So you got one out of three answers, right? But your spirit was three out of three. That's right. Your personality is three out of three. So in our hearts, you've won. And this has also given us, I think, a spectacular foundation for the next part of this episode.

So today on the show, what is a black hole star? Listen up. We also reveal some surprising exercise findings when it comes to lowering your risk. dementia and talk about a mammal that can shrink. You're listening to Shortwave, the science podcast from NPR. Okay, Elsa, you must want to start with the Black Hole Star, right? Like astronomy's awesome. You like it? Of course, especially after that miniature quiz. I'm ready for some redemption.

I am so hyped to beef up my space knowledge even more. So what the heckety heck is a Black Hole Star? Yeah, it's totally new to science. When the James Webb Space Saston, or JWST for short, started sending back pictures from very, very far away, meaning very early in the universe. They noticed something strange. All of these tiny little red dots they've never seen in space before. Oh, and did they have any idea what these little red dots might be?

I mean, they had ideas. They could have been galaxies or big stars or black holes, but nobody really knew for sure. And a recent study published in the journal Nature puts forward an answer for at least some of these mysterious red dots. It's a type of object that is a black hole star. Huh, what is that? Yeah, so it's a black hole with a super dense cloud of gas and dust around it, which is kind of like the atmosphere of a star.

But here's the difference. A regular star has basically a fusion reactor in its center. That's what makes it shine. But a black hole star does not. So instead, imagine if you had something like very dense layers of gas that instead of nuclear reactions at the center, you had a glowing black hole, a rapidly feeding black hole that was holding up this whole enterprise together. That's astronomer and lead author of the study Rohan Nidu at the University of Hawaii. These are not technically stars, but their light is

very star-like. Ooh, very cool. But why haven't we seen these before? You said these things are from the beginning of time. So what, did they go extinct or something? That's a really good scientific question. There's this long-standing mystery how supermassive black holes, like the one at the center of the Milky Way, become that giant, like millions of times the mass of our sun. These little red dots can provide an answer. Here's Anad de Groff, another astronomer involved in this study. So we think that little red dots could be this sort of this early growth spurt of a black hole or possibly even the birth of a supermassive black hole. And that is the most exciting part. Yeah, and Elsa, this all points to a new era of astronomy and discovery that the James Webb Space Telescope has ushered in, you know, finding new things much more often and getting one step closer to figuring out how these supermassive black holes form.

Very, very cool. Okay, let's move on to the next topic. It's well established as far as I understand that exercise can lower your risk of dementia. That's in part why I love to exercise. But now you're telling me there's some new studies saying only certain kinds of exercise. I hope I've been doing the right ones. Elsa, I think you have. I'm not a doctor, but yes, you have.

Because my brain is so good. So it might not be the type of exercise per se, but why you do it. So a new analysis in the journal, the Lancet Public Health, looked at 74 studies with more than 4 million participants. And they found that people who exercised by choice in their free time, like you, Elsa, you know, biking, hiking, they had lower risk of developing dementia. Compared to people who got their physical activity while commuting or at work. So, for example, people in physically demanding jobs actually showed a higher risk of developing dementia. Wow.

So lead author, Nathan Feeder at the University of Southern California, says this contradicts the popular belief that any exercise is good exercise. In terms of dementia prevention, every move might not count. Man, this seems like really crummy news for people who have very, very physical. So you're telling me that people who get their exercise from, say, physical labor at work do not get the same protection from dementia as someone who's just exercising in their leisure time? That seems so unfair. Yeah. Nathan says that this study seems to be uncovering some of the inequities between people who exercise for fun versus people who exercise for the job. People who exercise on the job, like lifting boxes or building houses, tend to be folks with lower socioeconomic status, which is associated with higher strength. more exposure to air and noise pollution, things scientists know are linked to a higher risk of dementia.

Yeah, clinical researcher Teresa Lou Ambrose at the University of British Columbia, who is not a part of this research, says it may also have to do with choice. There might be greater stress associated with the fact that you didn't choose to do this activity and that it's hard on you and you don't have a consistent break. And one thing this study might indicate is that some of these risk factors for dementia, we mentioned like higher stress, more exposure to air pollution, might weaken some of the of the benefits people see from exercising on the job. Okay. So this is probably stressful news for people who work in these jobs. Is there any silver lining? Yeah. So Teresa and Nathan do both point out that even

though the analysis looked at over 70 studies, only a handful looked at work-related exercise. So they could be missing some nuances in here. And Nathan says don't be stressed if you don't have much time or energy at the end of your day to exercise. Even just a few minutes is better than nothing. We know that if you increase five minutes a day of leisure, physical activity, we still see some benefits. Well, let's move on now to our final topic. Shrinking shrews, not shrieking shrews, shrinking. Shrinking shrews. They do shriek, I would assume.

But, yeah, shrews are these tiny mice-like mammals. It can be found all over the world. And some of them, including the long-clod shrew, which this study focuses on, have this super, wild way of getting through winter. So instead of fattening up like a bear or a groundhog to store up energy, they reduce the amount of energy they need by getting smaller. How do they get smaller? They get like skinnier?

They literally shrink, Elsa, like, honey, I shrunk the shrew. Here's Dina Deckman, behavioralologist at the Max Planck Institute. And this includes, for example, the brain, which shrinks by a quarter, and the skull, like the ossified bone and many, many organs. And yeah, it's super crazy. But then maybe even wilder is that when winter is over, they regrow that bone in organ tissue. Okay, I'm sorry, but this seems like a lot of work to save energy,

which is ironic. Yeah, evolution is a beautiful thing, right? So this is actually called Daniels phenomenon. And scientists have known about this since the 1950s, but Dana says research into it has really only taken off in the last decade or so in part because of interest from biomedical researchers. There's lots of interest from like osteoporosis research people or people who want to like regrow them.

And researchers or doctors who want to regrow brain tissue or livers, you name it. Are there any other shrinking animals besides shrinking shrews? Well, scientists have found that other animals that are small and have like high metabolisms, like moles and weasels, they can do this in the winter. But there's still a lot to learn about the. this whole process, which is what this new study published by the Royal Society really shows. Yeah, researchers in Japan found what they coined as reverse Danil's phenomenon in long-clod shrews, where the organs and bones shrink, but the snout gets longer in the winter.

So the lead author says they're not really sure why the snout grows, while other parts like the skull shrink, maybe to enhance their ability to like thermo-regulate, regulate their temperatures. But it does show like how highly adapted some of these tiny animals are to seasonal changes. If only we were so adapted. True, Elsa, that is so true. Elsa, thank you, as always, for kicking it with Shortwave.

Such a pleasure. If you, like me, love having as much Elsa in your life as possible, check out, consider this. NPR's afternoon podcast about what the news means for you. And if you liked this episode, check out our stories on what it's like to fall into a black hole

and how the brain cleans up its waist while you sleep. This episode was produced by Burley McCoy and Kai McNamee. It was edited by Rebecca Ramirez and Christopher in Taliazza. Tyler Jones checked the facts. Jimmy Keely and Ted Mebane were the audio engineers. I'm Regina Barber. And I'm Nate Rod. Thanks for listening to Shortwave, the science podcast from NPR.