AILSA CHANG, HOST:
It's time now for our science news roundup from Short Wave, NPR's science podcast. I'm joined by Regina Barber and Nate Rott from the show. Hey to both of you.
NATE ROTT, BYLINE: Hello.
REGINA BARBER, BYLINE: Hey.
CHANG: Hey. OK, so, as always, you guys have brought us three science stories that caught your attention recently. What is in store for all of us?
BARBER: Exploring what the heck is a black hole star.
ROTT: Why not all exercise may lower your dementia risk.
BARBER: And an in-depth look at shrinking shrews.
CHANG: Shrinking shrews - say that fast 50 times...
BARBER: Yeah.
CHANG: ...In a row.
ROTT: Shrinking shrews, shrinking shrews, shrinking shrews.
CHANG: (Laughter) OK. Let's start with the question, what the heck is a black hole star? Tell us.
BARBER: Yeah. It's totally new to science. When the James Webb Space Telescope, 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'd never seen in space before.
ROTT: Oh, and do they have any idea what these little red dots might be?
BARBER: I mean, they had ideas. They could have been galaxies or big stars or black holes, but nobody really knew for sure.
ROTT: And a recent study published in the journal Nature puts forward an answer for at least some of these mysterious red dots - a type of object that is a black hole star.
CHANG: What is that?
ROTT: Yeah. So it's a black hole with a superdense cloud of gas and dust around it, which is kind of like the atmosphere of a star.
BARBER: 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.
ROHAN NAIDU: So instead, imagine if you had something like very dense layers of gas, but 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.
ROTT: That's astronomer and lead author of the study Rohan Naidu at the University of Hawaii. These are not technically stars, but their light is very star-like.
CHANG: 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?
BARBER: 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 Anna de Graaff, another astronomer involved in this study.
ANNA DE GRAAFF: So we think the 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.
CHANG: Very, very cool. OK. 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...
BARBER: Yeah.
CHANG: ...Part why I love to exercise. But now you're telling me there's some new study saying only certain kinds of exercise. I hope I've been doing the right one.
ROTT: Ailsa, I think you have.
CHANG: (Laughter).
ROTT: I'm not a doctor, but, yes, you have. No, so...
CHANG: My brain is so good.
(LAUGHTER)
ROTT: 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, Ailsa - 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.
CHANG: Wow.
BARBER: So lead author Natan Feter, at the University of Southern California, says this contradicts the popular belief that any exercise is good exercise.
NATAN FETER: In terms of dementia prevention, every move might not count.
CHANG: Man, this seems like really crummy news for people who have very, very physical jobs. 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.
BARBER: Yeah. Natan 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 stress, more exposure to air and noise pollution - things scientists know are linked to a higher risk of dementia.
ROTT: Yeah. 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 benefits people see from exercising on the job.
CHANG: OK. So this is probably stressful news for people who work in these jobs.
BARBER: Yeah.
CHANG: Is there any silver lining?
ROTT: Yeah, so Teresa (ph) and Natan 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.
BARBER: And Natan 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.
FETER: We know that if you increase five minutes a day of leisure physical activity, we still see some benefits.
CHANG: Well, let's move on now to our final topic, shrinking shrews. Not shrieking shrews - shrinking, yeah?
ROTT: Shrinking shrews. They do shriek, I would assume. But yeah.
CHANG: (Laughter).
ROTT: Shrews are these tiny, mice-like mammals that can be found all over the world. And some of them, including the long-clawed shrew, which this study focuses on, have this super wild way of getting through winter.
CHANG: What?
BARBER: 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.
CHANG: (Laughter) How do they get smaller? They get, like, skinnier?
ROTT: They literally shrink, Ailsa. Like, honey, I shrunk the shrew.
CHANG: (Laughter).
ROTT: Here's Dina Dechmann, a behavior ecologist at the Max Planck Institute.
DINA DECHMANN: 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.
BARBER: But then, maybe even wilder, is that when winter is over, they regrow that bone and organ tissue.
CHANG: OK. I'm sorry, but this seems like a lot of work to save energy, which is ironic.
ROTT: Yeah. Evolution is a beautiful thing, right? So this is actually called Dehnel's phenomena (ph), and scientists have known about this since the 1950s. But Dina says research into it has really only taken off in the last, like, decade or so, in part because of interest from biomedical researchers.
DECHMANN: There's lots of interest from, like, osteoporosis research people or people who want to, like, regrow bone.
BARBER: And researchers or doctors who want to regrow brain tissue or livers, you name it.
CHANG: Are there any other shrinking animals besides shrinking shrews?
ROTT: 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 this whole process, which is what this new study published by the Royal Society really shows.
BARBER: Yeah. Researchers in Japan found what they coin as reverse Dehnel's phenomenon in long-clawed shrews, where the organs and bone shrink, but the snout gets longer in the winter.
ROTT: 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, thermoregulate, regulate their temperatures. But it does show, like, how highly adapted some of these tiny animals are to seasonal changes.
CHANG: That is so fascinating. That was Nate Rott and Regina Barber of NPR's science podcast Short Wave, where you can learn about new discoveries, everyday mysteries and the science behind the headlines. Thank you to both of you.
ROTT: Thank you.
BARBER: Thank you.
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