What is a black hole? Astro-Investigates Ep. 1 (Black Holes)

NASA explains what black holes are, how they form from collapsed stars, why they are not literal holes, and how scientists detect them.

Key Takeaways

Black holes are real, extremely dense objects whose gravity prevents light from escaping.
They form largely from collapsed stars and also exist as supermassive objects at galaxy centers.
Scientists detect black holes through their emissions, accretion disks, and gravitational waves.
Black holes remain a key testing ground for Einstein's general relativity and our understanding of physics.
Earth is not in any danger from nearby black holes.

What the video covers

Black holes are objects with gravity so intense that not even light can escape, formed in part from the gravitational collapse of dying stars.
Black holes were once considered only a mathematical curiosity, but in the 1950s and 1960s scientists realized they exist in the universe.
Supermassive black holes sit at the centers of galaxies and are much larger than stellar-mass black holes.
Black holes do not actively 'suck' matter in; objects can orbit them like any other massive body.
Infalling matter forms a hot, bright accretion disk; the first image of a black hole showed this glowing ring around a dark center.
Near a black hole, time appears to slow down, and a traveler could be stretched into a 'cosmic noodle' by spaghettification.
Stars passing too close can be torn apart in a tidal disruption event.
At the center of a black hole lies a point of infinite density where general relativity breaks down.
Black holes are found via X-rays, optical, ultraviolet, and infrared emissions, and via gravitational waves from merging black holes.
Cygnus X-1, the first confirmed black hole, was identified in 1964; NASA missions such as Chandra, Hubble, NuSTAR, and JWST continue to study them.

Chapters

Why are they called black holes?

A black hole is so compact that not even light can escape its gravitational pull. Because it emits no light, it appears black, which gives it its name.

Do black holes suck in everything nearby?

No. Black holes do not actively pull in matter; objects can orbit them just as they orbit other massive stars or objects. Only material that gets too close falls in.

How do scientists detect black holes?

Scientists find them by observing high-energy emissions such as X-rays, by seeing light from accretion disks, and by detecting gravitational waves produced when two black holes merge.

Full Transcript — Download SRT & Markdown

Speaker A

Out in space, there are places where gravity's influence is so intense that not even light can escape. These are known as black holes, objects with extreme gravity caused by extreme density that have an extreme influence on everything that gets too close. Often the subject of science fiction, black holes are science fact. But they're often misunderstood, as black holes aren't exactly holes.

Speaker A

of science fiction, black holes are science fact. But they're often misunderstood as black holes aren't exactly holes.

Speaker A

So let's investigate. What are black holes? A black hole is an object so compact that not even light can escape its gravitational potential. That's exactly where the name black hole comes from. It's black because it emits no light. Black holes used to be just a mathematical curiosity. But in the 1950s and 1960s, we actually realized they're out there in the universe. We know that there are black holes that have stellar masses that are born from the gravitational collapse, from the death of stars. We also know that there are much bigger black holes that sit at the center of galaxies. The critical thing to remember about what happens with anything that's near a black hole is that black holes don't suck.

Speaker A

the 1950s and 1960s, we actually realized they're out there in the universe. We know that there are black holes that have stellar masses that are born from the gravitational collapse, from the death of stars. We also know that there are much bigger black

Speaker A

You can orbit a black hole just as you can orbit any other star or any other massive object. Because there's so much mass in such a tiny volume, you can get a lot closer to all of that mass. As matter falls in towards a black hole, it starts spinning faster and faster. It will naturally form into a disk. We call it this accretion disk because that matter will accrete onto the black hole. And that disk gets incredibly hot, incredibly bright. A couple of years ago, we had the first image of a black hole, and that looked like a donut.

Speaker A

You can orbit a black hole just as you can orbit any other star or any other massive object. Because there's so much mass in such a tiny volume, you can get a lot closer to all of that mass. As matter falls in towards

Speaker A

But the donut was the matter around the black hole. The black hole itself was just a dark, you know, ominous void at the center. Black holes have extreme physics going on around them. All sorts of crazy things happening. Your perception when you got very close to a black hole is that time is slowing down. If a human traveler got too close to a black hole, they would first fall through feeling nothing until the point of spaghettification, where they would be stretched into a cosmic noodle.

Speaker A

we had the first image of a black hole and that looked like a donut.

Speaker A

When a star is passing by a black hole, one side of it gets greater gravity than the other. And so you get this very stretching effect. And so the star can be torn apart. This is what's called a tidal disruption event. What could be inside of a black hole? The most commonly accepted answer is a point of infinite density that we cannot really describe well. At this particular region within a black hole, all of our theory of general relativity breaks down.

Speaker A

got very close to a black hole is that time is slowing down. If a human traveler got too close to a black hole, they would first fall through feeling nothing until the point of spaghettification where they would be stretched into a cosmic noodle.

Speaker A

There are all sorts of ways of finding black holes. You can find them from their emission at certain wavelengths, like in the X-rays. We can see them in the optical, in the ultraviolet, in the infrared. Various NASA missions have been great at finding black holes. And then more recently, the really exciting way to find black holes is when two black holes merge, they create ripples in space-time, and you can detect that from gravitational wave observatories. One big mystery about astronomical black holes is how the large supermassive black holes that exist at the center of almost every galaxy actually got to be there. Another critical question is really what happens beyond the event horizon. What is essentially inside the black hole?

Speaker A

be inside of a black hole? The most commonly accepted answer is a point of infinite density that we cannot really describe well. At this particular region within a black hole, all of our theory of general relativity breaks down.

Speaker A

The real reason we want to know about these, as interesting as they are on their own, is that they are all connected with our general understanding of the physics of the universe. We're seeing black holes bigger than we had seen before. We're seeing black holes that weigh a hundred times the mass of the Sun. And right now, the community is trying to figure out where they're created. Einstein himself did not think such things would exist. Other people using his theory said, we could have things like this, like black holes. And now it's become sort of a bread-and-butter kind of study on many levels, to the point of us imaging them directly. I think it's one of the great stories of how science works, from pursuing ideas in terms of purely theoretical thought, but then observations coming in, and then merging the two to have a better understanding of the universe. The first black hole ever confirmed, Cygnus X-1, was first discovered back in 1964, when astronomers identified high-energy X-rays captured by a sounding rocket.

Speaker A

black holes. And then more recently, the really exciting way to find black holes is when two black holes merge, they create ripples in space -time and you can detect that from gravitational wave observatories. One big mystery about astronomical black holes is how the large supermassive black holes that exist at the center

Speaker A

Since then, NASA has launched a number of different missions and studies to further investigate black holes. These have included NASA's Chandra X-ray Observatory, the Hubble Space Telescope, NuSTAR, the James Webb Space Telescope, and many more. These are just a few examples of NASA's continued effort to expand our understanding of black holes. Thankfully, as humans living on planet Earth, we will never be close enough to any black hole, including the supermassive black hole at the center of our own galaxy, to ever be in danger of falling in. I promise.

Speaker A

The real reason we want to know about these, as interesting as they are on their own, they are all connected with our general understanding of the physics of the universe. We're seeing black holes bigger than we had seen before. We're seeing black holes

Speaker A

that weigh a hundred times the mass of the sun. And right now, the community is trying to figure out where they're created. Einstein himself did not think such things would exist. Other people using his theory said, we could have things like this, like

Speaker A

black holes. And now it's become sort of a bread and butter kind of study on many levels to the point of us imaging them directly. I think it's one of the great stories of how science works, from pursuing ideas

Speaker A

in terms of purely theoretical thought, but then observations coming in and then merging the two to have a better understanding of the universe. The first black hole ever confirmed, Cygnus X -1, was first discovered back in 1964, when astronomers identified high -energy X -rays captured by a sounding rocket.

Speaker A

Since then, NASA has launched a number of different missions and studies to further investigate black holes. These have included NASA's Chandra X -ray Observatory, the Hubble Space Telescope, new star, the James Webb Space Telescope, and many more.

Speaker A

These are just a few examples of NASA's continued effort to expand our understanding of black holes. Thankfully, as humans living on planet Earth, we will never be close enough to any black hole, including the supermassive black hole at the center of our own galaxy to ever be in danger

Speaker A

of falling in. I promise.

Topics:black holesNASAastronomyaccretion diskspaghettificationCygnus X-1gravitational wavessupermassive black holegeneral relativityspace science

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