ARI SHAPIRO, HOST:

Time now for our science news roundup from our friends at NPR's Short Wave podcast, Aaron Scott and Regina Barber. Good to have you both back.

AARON SCOTT, BYLINE: Hi, Ari.

REGINA BARBER, BYLINE: Yeah, it's good to be here, Ari.

SHAPIRO: As usual, you've brought us three science stories that grabbed you this week. What's on the menu?

BARBER: We got a black hole that's both super big and the oldest confirmed.

SCOTT: And then how rising temperatures and pollution are tipping the balance of the sexes, at least for sea turtles.

BARBER: And the potential health benefits of cutting a teaspoon of salt in your diet.

SHAPIRO: OK, let's start with a black hole - the oldest one scientists have been able to confirm?

BARBER: Yeah, and it's ginormous. It's called a supermassive black hole. It's super far away from us, which means we're seeing what it looked like just 470 million years after the universe was created. And this really early period of time in the universe was something astronomers didn't have much data for - just a lot of theories.

SCOTT: Until now. So the James Webb Space Telescope is allowing us to test all those theories. By letting us look this far back in time, it works kind of like a time machine to study how bits of the universe came together - like, in this case, this supermassive black hole.

BARBER: And Ari, these supermassive black holes - they exist at the center of almost every galaxy in the universe, including ours, the Milky Way. And they shape how galaxies form.

SHAPIRO: And what do scientists hope to learn by finding these enormous, ancient black holes?

BARBER: Well, they're trying to solve a mystery, which is how these supermassive black holes form at all. They know one way to make black holes, for sure. And that's when a massive star dies - like, much, much bigger than our sun - they explode, they collapse, and they create a black hole.

SCOTT: But supermassive black holes are thousands of times the mass of our sun, and they couldn't have been made just by dying stars. They're just too big.

BARBER: Yeah. And Priya Natarajan is a theoretical astrophysicist at Yale. And way back in 2006, she and her colleagues proposed that a supermassive black hole could get their start by a huge amount of dust and gas collapsing and then grow from there, rather than from a dying star.

SCOTT: But they needed evidence for this theory, and that's where the detection of this really old supermassive black hole comes in. Priya co-authored this latest research in the journal Nature Astronomy, and it provides some evidence in favor of their theory on how these things form from collapsing clouds of gas and not from collapsing stars.

SHAPIRO: How - but she first floated this theory nearly 20 years ago. Why did it take so long to demonstrate this?

BARBER: Yeah. She said it took three space telescopes to verify this - the Hubble Space Telescope, the new James Webb Space Telescope - or JWST - and the Chandra X-ray Observatory.

PRIYA NATARAJAN: And it's kind of a miraculous lining up of things - right? - because all three NASA flagship missions were involved in this.

BARBER: And Priya says, thanks to JWST in particular, we're getting a window into what's happening in the early universe. And this discovery is just opening it up just a crack.

SHAPIRO: All right. From massive, ancient black holes, let's go to tiny baby sea turtles. And climate change and pollution are endangering sea turtles by skewing the balance of females to males. How?

SCOTT: Yes, yes. So let's take the two apart - first temperature. Fun science fact for you, Ari - if you change the temperature of a sea turtle egg along with a number of other reptile eggs, you can actually change the sex of the embryo. It's called temperature-dependent sex determination.

BARBER: And this happens because hotter and cooler temperatures activate different genes that produce either female or male sex hormones. And in the case of sea turtles, rising temperatures on the beaches where they bury their eggs push the embryos to become female.

SCOTT: And we are not talking about a slight imbalance here. This is huge. In warmer places, like the northern part of the Great Barrier Reef, over 99% of the hatchlings are female - 99%.

SHAPIRO: Wow. OK, so that's how temperature affects the balance of male to female. What about pollution?

BARBER: Yeah. Well, the scientists who conducted this research realized that temperature couldn't explain everything, so they wondered if something else was playing a role.

SCOTT: And previous research had shown that heavy metals and some other contaminants can disrupt hormones for other reptiles, like alligators, and cause them to have skewed sex ratios, so these researchers decided to test green sea turtle nests for a number of these pollutants. This is Arthur Barraza, the lead author of the paper that came out this week in Frontiers in Marine Science.

ARTHUR BARRAZA: One of the things that I found was that certain heavy metals were associated with more females in the nest than predicted.

BARBER: Things like cadmium and antimony, along with a couple organic chemicals - basically compounds that come from things like urban runoff, mining and fossil fuels and plastic waste.

SCOTT: And Arthur says this isn't really a problem now, but it could be a big threat to the survival of turtles in coming years because they'll have an incredibly difficult time finding a mate and reproducing. I mean, you can imagine that turtle Tinder is just going to be tumbleweeds.

SHAPIRO: Terrible.

SCOTT: (Laughter).

SHAPIRO: OK, so what can we do about it?

BARBER: Yeah. Conservationalists (ph) are experimenting with using seawater to irrigate turtle nests to cool them down and create a more mixed ratio of the sexes.

SHAPIRO: So they're watering turtle nests to grow the next generation of males.

SCOTT: Uh-huh. Yeah, there's a joke in there somewhere, probably.

SHAPIRO: Let's end on the third story you've brought us - this research about salt and blood pressure. And I'm going to take a wild guess and say that eating more salt drives your blood pressure up.

BARBER: Yeah. So cutting it is going to make it better. Cutting one teaspoon of salt a day results in a decline of blood pressure comparable to taking medication, actually.

SHAPIRO: Just one teaspoon? Wow.

BARBER: Yeah.

SCOTT: Yeah. And this is from a new study published in JAMA, or the Journal of the American Medical Association. And before we go further, we should start with just some basics. So we mentioned salt, like table salt. But the thing we're really talking about is sodium, which is in the salt.

BARBER: Right. And we know we need some sodium for our bodies to work properly. It plays an important role, for instance, in nerve and muscle function. But too much sodium is bad for our health. Like, for some of us, it can contribute to high blood pressure, which can cause stroke or heart disease.

SHAPIRO: How exactly does that work? Why does salt make blood pressure go up?

BARBER: It has to do with our bodies absorbing more water because of the salt. Like, so extra sodium in your blood pulls more water into your blood vessels, increasing the amount of blood in your blood vessels.

SCOTT: And that, in turn, increases the pressure, leading in some people to high blood pressure. Or if you already have high blood pressure, it could make it worse, and then all of this can result in damage to your blood vessels and organs.

SHAPIRO: It sounds, from this study, like people don't have to make a dramatic change in their diet to have a real impact.

SCOTT: Yeah. They saw these blood-pressure-lowering effects in just one week, even for people already on blood pressure medication. So quick effects - but it's not necessarily going to be easy, Ari. According to the FDA, Americans eat on average about 3,400 mg of sodium per day, and a teaspoon of table salt has about 2,300 mg of sodium in it. So in this case, you're going to need to cut your daily sodium intake by two-thirds.

SHAPIRO: Oh, forget that.

BARBER: Yeah (laughter).

SCOTT: Yeah.

BARBER: And for many of us, this sodium actually comes from packaged and prepared foods, so maybe just make sure you check out those nutritional labels. Bottom line, though, the researchers say that really any amount of sodium reduction in your diet, for most people, will be better for your blood pressure compared to no reduction at all.

SHAPIRO: You know what? We all have our vices, and I'm not giving up french fries.

(LAUGHTER)

SHAPIRO: That is Regina Barber and Aaron Scott of NPR's science podcast, Short Wave, where you can learn about new discoveries, everyday mysteries and the science behind the headlines. Regina, Aaron, thank you.

BARBER: Thank you, Ari.

SCOTT: Thank you.

(SOUNDBITE OF MUSE SONG, "SUPERMASSIVE BLACK HOLE") Transcript provided by NPR, Copyright NPR.

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