NASA’s Curious Universe

Episode Title:“Inside a Black Hole”

Introducing NASA’s Curious Universe

Our universe is a wild and wonderful place. Join NASA astronauts, scientists, and engineers on a new adventure each week — all you need is your curiosity. Visit our space laboratory, meet the slow-moving crawlers that transport rockets to the launch pad, and dive into faraway galaxies where black holes form. First-time space explorers welcome.

About the Episode

Don’t let the name fool you: a black hole is anything but empty space. Black holes are some of the most extreme, bizarre and fascinating objects in the universe. Regina Caputo and Jeremy Schnittman describe what it might be like to go hunting for one.

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REGINA CAPUTO:Say you were floating towards the black hole… Basically, the first part of you would start to experience the really extreme gravity. Your body would basically start to be stretched like a, like a spaghetti, stretching to get into the black hole where we would never see you again. Once you’re in, you’re stuck and that becomes your universe…

HOST PADI BOYD:This is NASA’s Curious Universe. Our universe is a wild and wonderful place. I’m PadiBoyd, and in this podcast, NASA is your tour guide!

HOST PADI BOYD:This week’s adventure will give you a front row seat to some of the universe’s most perplexing wonders… we’re exploring black holes.

REGINA CAPUTO:Really, these are the, some of the most extreme environments in the universe.

HOST PADI BOYD:That’s Regina Caputo, she’s an astrophysicist at NASA, and she studies black holes – mysterious and fascinating cosmic objects.

REGINA CAPUTO:…We can’t make anything like a black hole on earth to study it. And so if we really want to how gravity interacts with all of the other forces in the universe, like it’s really a playground for understanding how gravity works, how fundamental particles work, how stars collapse in on themselves… [fades out]

HOST PADI BOYD:Black holes truly are one of a kind. But what exactly is a black hole?

HOST PADI BOYD:Let’s start with the word “Black”. The name comes from the fact that nothing can escape the gravity of a black hole, not even light.

HOST PADI BOYD:How can they keep such a tight hold on everything? Well they are extremely massive.

REGINA CAPUTO: And so they have very strong gravitational, attractive forces. And so they really don’t like suck things in, they pull things in because that’s how gravity works. It’s things that have mass are all attracted to each other.

HOST PADI BOYD:And the more mass, the more gravity! Even though light travels so quickly, it is no match for the gravity of a black hole.

HOST PADI BOYD:So now you know why they’re black, let’s talk about why they’re called “holes”. This is actually a misleading word to describe these massive objects.

HOST PADI BOYD:While they may seem like a hole in the sky because they don’t produce light, a black hole is not empty, It’s actually a lot of matter condensed into a single point. This point is known as a singularity.

HOST PADI BOYD:So how do we get such a large amount of mass to come together at one point in space? Step one: get yourself a large star.

JEREMY SCHNITTMAN:These big stars burn up their fuel really fast because they have more gravity, which makes the centers of them hotter and denser. So the they can go through a lot more nuclear reactions and they burn it all up really, really fast.

HOST PADI BOYD:That’s Jeremy Schnittman, a research astrophysicist at NASA. He’s going to explain how a star gives rise to a black hole as it eats up its fuel…

JEREMY SCHNITTMAN:They build up a big pile of ashes in the center of the star, those ashes. Actually, it’s iron. That iron doesn’t do nuclear burning, so it doesn’t give off, extra heat just sits there and it’s getting bigger and bigger and bigger.

HOST PADI BOYD:And now you have these two forces that are battling against each other. One force comes from whatever fuel is left to be burned. And another force is from the gravity of the iron pulling everything inward.

JEREMY SCHNITTMAN: And eventually you run out of heat, you run out of this pressure that’s holding up the center of the star, and the gravity just keeps getting bigger and the pressure stays more or less the same. And sothe gravity wins, and when the gravity wins… everything just starts collapsing.

HOST PADI BOYD: At that moment, two things are happening. Some star stuff is being shot off into space, causing the light shows we call supernovae. And the rest of it condenses into one point, the singularity.

HOST PADI BOYD:And that folks, is how you make a stellar black hole. It’s called “Stellar” because it was made from a star.

HOST PADI BOYD:Our Sun is a star – so you may be asking, will it ever become a black hole?

HOST PADI BOYD:Our Sun will never form an iron core massive enough to collapse into a black hole. In fact, the smallest black hole we’ve ever observed was about four times the mass of the Sun. Instead of a black hole, our Sun will evolve into something else.

REGINA CAPUTO:But at some point in our Sun’s lifetime it will puff up into a red giant phase. And so it’ll get really, really, really big. Future humans will have to deal with that, but it’s very, very far in the future [laugh].

HOST PADI BOYD: By far in the future, Regina means really far… about 4 billion years.

HOST PADI BOYD:If our sun weremagically replaced by a black hole of the same mass, here’s what would happen.

HOST PADI BOYD: Earth and all of the other planets would stay in their same orbits, experiencing the same amount of gravity as before.

REGINA CAPUTO:We wouldn’t even notice, like the Earth would still rotate around.

HOST PADI BOYD:The major difference? No light. A solar system in darkness. Not a fun scenario!

HOST PADI BOYD:So Jeremy took you through the birth of a stellar mass black hole, but that’s not the only kind of black hole that we know of.

HOST PADI BOYD:There’s another kind of black hole that makes a stellar mass black hole look like a blip in the universe.

JEREMY SCHNITTMAN:There are the supermassive black holes that are millions or even billions of times more massive than the Sun. And those are in the, the centers of almost every galaxy and we still don’t really know where those come from, but they seem to be quite universal.

HOST PADI BOYD:In fact, we have one of these mysterious giants at the center of our galaxy.

HOST PADI BOYD:About 26,000 light years from Earth, the equivalent of 150 quadrillion miles, is the Milky Way’s supermassive black hole called Sagittarius A*. It’s called that because it is located in the constellation Sagittarius.

HOST PADI BOYD: And you might be surprised to know that it wasn’t discovered until 1974.

HOST PADI BOYD:Which raises the question, If you were hunting for a black hole, how would you know when you had found one? After all, they are black!

REGINA CAPUTO:You can’t actually see a black hole cause they don’t produce light like stars do.

HOST PADI BOYD: However black holes can be some of the brightest objects in the sky. That’s because of what can happen before black holes gobble up star stuff.

HOST PADI BOYD: Around a black hole is a boundary called the event horizon. Anything that passes the event horizon is trapped within the black hole. But right as gas and dust get closer and closer to the event horizon, the gravity from the black hole makes them spin really fast… forming lots of radiation.

REGINA CAPUTO:And so we see that last little bits of light escaping from the event horizon…

HOST PADI BOYD:Another clue that there is a black hole is when you see a star orbiting what appears to be nothing… at a very fast pace. That’s how Cygnus X-1, the first ever confirmed black hole, was found in the 70’s.

JEREMY SCHNITTMAN:We saw this star orbiting around something, and we didn’t know what it was orbiting around. There were a lot of X rays coming from it. And we figured that the only way it could be moving that fast is if there’s a really strong gravitational field pulling on it. Since there’s really nothing else that it could have been and it was more or less invisible. That’s how we concluded that it was in fact, a black hole.

HOST PADI BOYD:Cygnus X-1 was a big deal – finding it confirmed what until then had only been a mathematical prediction based on Einstein’s theory of relativity. Since then, we’ve found black holes through other means. Like sometimes, a black hole can reveal itself if it comes in between Earth and a bright star.

JEREMY SCHNITTMAN:Gravity actually bends light, bends the trajectory of photons.

HOST PADI BOYD:The gravity of the black hole bends the space surrounding it, so the light from the star travels through this warped space and looks very strange…kind of like a cosmic donut. It’s a phenomenon called gravitational lensing.

HOST PADI BOYD:And finally, there’s one more way we can detect black holes. One that requires that two black holes get very close to each other.

REGINA CAPUTO:…And then they start orbiting around each other and basically get closer and closer and closer and closer together as they’re spiraling towards each other. And at some point their event horizons merge, and they smash into each other.

HOST PADI BOYD: And this process literally shakes the fabric of space time. We’ve observed this before, and in some ways we’ve heard it, too. We’ve detected these waves with LIGO – the Laser Interferometer Gravitational-wave Observatory. LIGO is funded by the National Science Foundation and operated by Caltech and MIT.

REGINA CAPUTO:That smashing together of these very, very massive objects sends out ripples in space time. And those ripples are just like sound waves and LIGO is built to detect those ripples.

HOST PADI BOYD:Scientists took those ripples and translated them into audio waves so that wecan hear it. Take a listen. First you’ll hear the sound at the original frequency corresponding to the gravitational waves.

HOST PADI BOYD:Now here is the sound played at a higher frequency that is easier for us to hear.

HOST PADI BOYD:Did you hear the “woop” sound? That was the waves getting faster and faster as the black holes merged.

REGINA CAPUTO:And so that’s how we get the sounds of the universe.

HOST PADI BOYD:All of these ways of detecting black holes require that some other object be present. But, if the black hole is flying solo, with nothing nearby orbiting it and nothing nearby to eat, there is little chance that we will ever notice it.

HOST PADI BOYD:We will likely only get to know a fraction of the millions if not a billion stellar mass black holes that are estimated to live in the Milky Way alone…

PADI BOYD:Stellar mass and supermassive black holes are vastly different in mass. And for a while, scientists thought there might be no black holes with masses in between these two extremes. But recently, with the help of the Hubble Space Telescope, astrophysicists found the best evidence yet of intermediate-mass black holes. NASA’s Chandra and NuStar telescopes have also been exploring these newly discovered middleweights.

HOST PADI BOYD:Now, it’s time for us to explore a black hole up close and personal. Let’s take a journey into one!

REGINA CAPUTO:So say you were floating towards the black hole.

HOST PADI BOYD:Now let’s suppose that you are approaching a stellar mass black hole, and that it isn’t actively consuming star stuff, because if it were, even being near the black hole could be deadly.

REGINA CAPUTO:I certainly would not want to be in the path of a black hole. That’s actively eating up these stars. They eat things and then they kind of like, you know, burp up particles, you know, at the speed of light.

HOST PADI BOYD: Lots of high energy particles do not mix well with life. So let’s just assume you approach a lonely black hole by chance – because you wouldn’t see it. Now as you get closer, all of the sudden, you start feeling this tugging on one side of your body, but not on the other.

REGINA CAPUTO:Basically the first part of you that was starting to get closer and closer to the black hole would start to experience the really extreme gravity that was near the black hole. Say if you were going feet first, you know, your feet would start to be stretched apart basically like a spaghetti.

JEREMY SCHNITTMAN:There’s even a technical term for it. It’s called spaghettification. Basically, just rip you to pieces.

REGINA CAPUTO:You probably wouldn’t survive.

PADI BOYD:But, just for fun, let’s say you did survive.

REGINA CAPUTO:Part of you would cross over into the event horizon and the rest of you would probably be following pretty soon after.

PADI BOYD:This onlyhappens with stellar mass black holes where you can feel that change in gravity. But, if you found yourself entering a supermassive black hole, you wouldn’t feel a thing! All of a sudden, you just would be inside the black hole, never to be seen again. Well, kind of…

PADI BOYD:Here’s the crazy part. If your friend were watching this happen to you, they might see you get stretched – but it would happen really slowly until at some point it might look like you were frozen in time… like you never passed through the event horizon.

PADI BOYD:That’s because time gets stretched out by the immense gravity that black hole produces.

JEREMY SCHNITTMAN:Really, it bends the, the reality of our universe.

PADI BOYD:And the reverse happens from your vantage point. So, if you were looking out at your friend, it would seem like they were moving through life at warp speed.

PADI BOYD:If somehow you weren’t ripped apart by the gravity, or managed to survive the radiation near the black hole’s event horizon, well then you would get to enter the black hole.

REGINA CAPUTO:Once you’re in, you’re stuck and that becomes your universe.

PADI BOYD:What would you see and feel? We don’t really know. We can only theorize. But at some point, you would become one with the singularity. Essentially, you’d be compressed into a tiny speck.

REGINA CAPUTO:So I would not recommend traveling to black holes [laugh]. At least not that close [laugh].

PADI BOYD:And luckily it shouldn’t be too tricky to avoid them.

HOST PADI BOYD:The nearest black holes we know of are thousands of light– years away from us, meaning it would take thousands of years to get to them if we could travel at the speed of light, which we can’t. So not only will they not be eating Earth, they are too far away for a visit from earthlings.

HOST PADI BOYD: By now, the universe is peppered with black holes with new ones forming all the time. And some black holes keep expanding as they consume more gas. But how and when does a black hole die?

JEREMY SCHNITTMAN:Even the ones that are, you know, accreting hot gas and are very bright, they only do that for a very short part of their lifetime but eventually, they’ll all just run out of fuel, if even if they have a star orbiting around them that won’t last forever. There’s nothing left for them to do. They’re just gonna they’re just gonna sit there.

HOST PADI BOYD:And for the most part, all of the matter inside the black hole will stay there as well.

JEREMY SCHNITTMAN: What happens in a black hole stays in a black hole.

HOST PADI BOYD: There is only one theorized way that anything can escape a black hole’s gravitational grip.

JEREMY SCHNITTMAN:There’s a interesting result from Stephen Hawking, the famous theoretical physicist who showed that because of these quantum mechanical effects, a tiny bit of radiation can actually leak out of a black hole. This is called Hawking radiation. But in practice, it’s such a tiny, tiny, tiny effect. First, we will never be able to observe it. And second, if you have a star that’s 10 or 15 times the size of the sun, it would take trillions and trillions of years before you’re even changed a little bit because of the Hawking radiation.

REGINA CAPUTO:Once you hit black hole, you’re black hole for the rest of the universe it seems like..

HOST PADI BOYD:The long lasting nature of black holes leads scientists to speculate that towards the end of the universe, when there is no stuff left to make new stars, and when all of the existing stars have burnt up, the universe will be dominated by black holes – a dark and uninviting scenario.

HOST PADI BOYD: Until, eventually, those dissipate trillions upon trillions of years later – more time than we can fathom.

HOST PADI BOYD: And then, there will be nothing.

HOST PADI BOYD:This is NASA’s Curious Universe. This episode was written by Margot Wohl and Maddie Arnold. The Curious Universe team includes Micheala Sosby and Vicky Woodburn. Our executive producer is Katie Atkinson.

HOST PADI BOYD: Special thanks to Claire Andreoli, Ryland Heagy, Barb Mattson, Erin Kara and the Astrophysics team.

HOST PADI BOYD:If you liked this episode, please let us know by leaving us a review, tweeting about the show @ NASA, and sharing us with a friend…

HOST PADI BOYD:To keep up with the latest black holes science from NASA, check out NASA.gov/blackhole

HOST PADI BOYD:Still curious about NASA? You can send us questions about this episode or a previous one and we’ll try to track down the answers!

HOST PADI BOYD:You can email a voice recording or send a written note to NASA-CuriousUniverse@mail.NASA.gov. Go to nasa.gov/curiousuniverse for more information.

HOST PADI BOYD:Thank you for listening to the second season of NASA’s Curious Universe. We’ve enjoyed taking you along with us as we explored everything from the international space station to our asteroid hunting mission! We’re taking a break now, but we’ll be back before you know it.

HOST PADI BOYD:Until then, you can continue exploring the universe and discovering our home planet with NASA by visiting nasa.gov. You can also follow NASA on Twitter, Instagram and Facebook. And, find more NASA podcasts in your app or at nasa.gov/podcasts.

HOST PADI BOYD:Before we sign off, we asked our scientists to do their best impression of the sounds we can make from black hole data. Here’s what they gave us…