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New images shed light on the supermassive blackhole at the center of the Milky Way

AILSA CHANG, HOST:

Sagittarius A is this supermassive black hole at the center of our galaxy, the Milky Way. And in 2022, scientists gave us the first-ever look at that black hole. Those images showed a fuzzy orange blob encircling a dark center, kind of like an orange donut. Yummy. Now, astronomers have released an even more detailed portrait of Sagittarius A. It depicts beautiful swirls of magnetic fields spiraling out from the edges of this massive gravity monster. Here to tell us more is Sara Issaoun. She's an observational astronomer on the Event Horizon Telescope team. Welcome.

SARA ISSAOUN: Thank you. I'm glad to be here.

CHANG: And so glad to have you. So I know these images can be years in the making, right? Like, what was particularly challenging about coming up with this new image of Sagittarius A?

ISSAOUN: So our Milky Way black hole, Sagittarius A*, is kind of a problem child black hole in that it's quite small in size, which...

CHANG: Oh.

ISSAOUN: ...Means that the gas around it varies much quicker as we would see it from Earth. So taking a long exposure photo is really, really challenging and took the team a lot more time to deal with.

CHANG: Can I also ask - because I need you to explain something I cannot quite wrap my head around. And that is if black holes get their name because their gravitational pull is so strong that light cannot escape, what are you actually taking a picture of? - because don't you need light to take any photo?

ISSAOUN: Exactly. So at the center of the photo, there's this kind of central darkness patch. That is where the black hole resides.

CHANG: OK.

ISSAOUN: And what we're seeing around it, this bright ring of light, is actually light coming from very, very hot, glowing gas near the black hole that is about to fall into the black hole and is glowing radiation. And then it escapes and travels, you know, millions of light years to get to us and form this beautiful image that we see.

CHANG: That is so cool. And you aren't even using a regular telescope, right? Like, you've linked a bunch of telescopes all over the planet to make, essentially, the way I understand it, an Earth-sized telescope, right?

ISSAOUN: Exactly because even though these supermassive black hole objects are enormous in size, Sagittarius A* is actually the size of the orbit of Mercury around the sun.

CHANG: Wow.

ISSAOUN: It's also 26,000 light years away from us at the center of our galaxy, so it looks really, really small as seen from Earth. So in order to be able to make an image of it, we need a very large telescope. And since we can't really build a kind of Death Star telescope the size of the Earth...

CHANG: (Laughter).

ISSAOUN: ...We had to come up with a clever technique. So this technique involves connecting telescopes that are already there on the Earth to synthesize a virtual telescope that has the magnifying power that, if you hold up your thumb at the end of your arm, you would be able to see the atoms that compose your thumb with the power of the Event Horizon telescope.

CHANG: Wow. That is so amazing. You know, the first image we saw of Sagittarius A, it was, like, this fuzzy orange donut, right? But then this latest photo, it looks a lot sharper. You can actually see the streaks of orange spiraling out of a dark center point. Can you explain more, like, what is happening there? What's - what changed?

ISSAOUN: Right, so what we're seeing in this new image is an added dimension to the information we had before. Now we're only looking at part of the light that's coming from the hot gas around the black hole that is polarized. And this polarized light is what teaches information about the mechanisms around how a black hole feeds and how its magnetic fields look like. And it feeds gas very, very slowly. So on human scales, if you were to have the same kind of diet as Sagittarius A*, you would eat about one grain of rice every million years.

CHANG: Oh, my God.

ISSAOUN: So I don't recommend...

CHANG: That's brutal.

ISSAOUN: ...It.

(LAUGHTER)

ISSAOUN: Yeah, it's not great.

CHANG: I feel sorry for Sagittarius A right now.

ISSAOUN: I know. Yeah, it's very underfed.

CHANG: But I don't want it to be so well fed that it ends up gobbling our sun and all the planets around it, so, OK, maybe we'll keep Sagittarius A on a diet.

ISSAOUN: Yes.

CHANG: That is astronomer Sara Issaoun of the Event Horizon Telescope Collaboration. Thank you so much.

ISSAOUN: Thank you. Transcript provided by NPR, Copyright NPR.

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Kai McNamee
[Copyright 2024 NPR]
Christopher Intagliata is an editor at All Things Considered, where he writes news and edits interviews with politicians, musicians, restaurant owners, scientists and many of the other voices heard on the air.
Ailsa Chang is an award-winning journalist who hosts All Things Considered along with Ari Shapiro, Audie Cornish, and Mary Louise Kelly. She landed in public radio after practicing law for a few years.