Black Hole Week - Blog Posts

Our Weird and Wonderful Galaxy of Black Holes

Black holes are hard to find. Like, really hard to find. They are objects with such strong gravity that light can’t escape them, so we have to rely on clues from their surroundings to find them.

When a star weighing more than 20 times the Sun runs out of fuel, it collapses into a black hole. Scientists estimate that there are tens of millions of these black holes dotted around the Milky Way, but so far we’ve only identified a few dozen. Most of those are found with a star, each circling around the other. Another name for this kind of pair is a binary system.That’s because under the right circumstances material from the star can interact with the black hole, revealing its presence. 

The visualization above shows several of these binary systems found in our Milky Way and its neighboring galaxy. with their relative sizes and orbits to scale. The video even shows each system tilted the way we see it here from our vantage point on Earth. Of course, as our scientists gather more data about these black holes, our understanding of them may change.   

If the star and black hole orbit close enough, the black hole can pull material off of its stellar companion! As the material swirls toward the black hole, it forms a flat ring called an accretion disk. The disk gets very hot and can flare, causing bright bursts of light.

V404 Cygni, depicted above, is a binary system where a star slightly smaller than the Sun orbits a black hole 10 times its mass in just 6.5 days. The black hole distorts the shape of the star and pulls material from its surface. In 2015, V404 Cygni came out of a 25-year slumber, erupting in X-rays that were initially detected by our Swift satellite. In fact, V404 Cygni erupts every couple of decades, perhaps driven by a build-up of material in the outer parts of the accretion disk that eventually rush in. 

In other cases, the black hole’s companion is a giant star with a strong stellar wind. This is like our Sun’s solar wind, but even more powerful. As material rushes out from the companion star, some of it is captured by the black hole’s gravity, forming an accretion disk.

A famous example of a black hole powered by the wind of its companion is Cygnus X-1. In fact, it was the first object to be widely accepted as a black hole! Recent observations estimate that the black hole’s mass could be as much as 20 times that of our Sun. And its stellar companion is no slouch, either. It weighs in at about 40 times the Sun.

We know our galaxy is peppered with black holes of many sizes with an array of stellar partners, but we've only found a small fraction of them so far. Scientists will keep studying the skies to add to our black hole menagerie.

Curious to learn more about black holes? Follow NASA Universe on Twitter and Facebook to keep up with the latest from our scientists and telescopes.

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What’s Inside a ‘Dead’ Star?

Matter makes up all the stuff we can see in the universe, from pencils to people to planets. But there’s still a lot we don’t understand about it! For example: How does matter work when it’s about to become a black hole? We can’t learn anything about matter after it becomes a black hole, because it’s hidden behind the event horizon, the point of no return. So we turn to something we can study – the incredibly dense matter inside a neutron star, the leftover of an exploded massive star that wasn’t quite big enough to turn into a black hole.

Our Neutron star Interior Composition Explorer, or NICER, is an X-ray telescope perched on the International Space Station. NICER was designed to study and measure the sizes and masses of neutron stars to help us learn more about what might be going on in their mysterious cores.

When a star many times the mass of our Sun runs out of fuel, it collapses under its own weight and then bursts into a supernova. What’s left behind depends on the star’s initial mass. Heavier stars (around 25 times the Sun’s mass or more) leave behind black holes. Lighter ones (between about eight and 25 times the Sun’s mass) leave behind neutron stars.

Neutron stars pack more mass than the Sun into a sphere about as wide as New York City’s Manhattan Island is long. Just one teaspoon of neutron star matter would weigh as much as Mount Everest, the highest mountain on Earth!

These objects have a lot of cool physics going on. They can spin faster than blender blades, and they have powerful magnetic fields. In fact, neutron stars are the strongest magnets in the universe! The magnetic fields can rip particles off the star’s surface and then smack them down on another part of the star. The constant bombardment creates hot spots at the magnetic poles. When the star rotates, the hot spots swing in and out of our view like the beams of a lighthouse.

Neutron stars are so dense that they warp nearby space-time, like a bowling ball resting on a trampoline. The warping effect is so strong that it can redirect light from the star’s far side into our view. This has the odd effect of making the star look bigger than it really is!

NICER uses all the cool physics happening on and around neutron stars to learn more about what’s happening inside the star, where matter lingers on the threshold of becoming a black hole. (We should mention that NICER also studies black holes!)

Scientists think neutron stars are layered a bit like a golf ball. At the surface, there’s a really thin (just a couple centimeters high) atmosphere of hydrogen or helium. In the outer core, atoms have broken down into their building blocks – protons, neutrons, and electrons – and the immense pressure has squished most of the protons and electrons together to form a sea of mostly neutrons.

But what’s going on in the inner core? Physicists have lots of theories. In some traditional models, scientists suggested the stars were neutrons all the way down. Others proposed that neutrons break down into their own building blocks, called quarks. And then some suggest that those quarks could recombine to form new types of particles that aren’t neutrons!

NICER is helping us figure things out by measuring the sizes and masses of neutron stars. Scientists use those numbers to calculate the stars’ density, which tells us how squeezable matter is!

Let’s say you have what scientists think of as a typical neutron star, one weighing about 1.4 times the Sun’s mass. If you measure the size of the star, and it’s big, then that might mean it contains more whole neutrons. If instead it’s small, then that might mean the neutrons have broken down into quarks. The tinier pieces can be packed together more tightly.

NICER has now measured the sizes of two neutron stars, called PSR J0030+0451 and PSR J0740+6620, or J0030 and J0740 for short.

J0030 is about 1.4 times the Sun’s mass and 16 miles across. (It also taught us that neutron star hot spots might not always be where we thought.) J0740 is about 2.1 times the Sun’s mass and is also about 16 miles across. So J0740 has about 50% more mass than J0030 but is about the same size! Which tells us that the matter in neutron stars is less squeezable than some scientists predicted. (Remember, some physicists suggest that the added mass would crush all the neutrons and make a smaller star.) And J0740’s mass and size together challenge models where the star is neutrons all the way down.

So what’s in the heart of a neutron star? We’re still not sure. Scientists will have to use NICER’s observations to develop new models, perhaps where the cores of neutron stars contain a mix of both neutrons and weirder matter, like quarks. We’ll have to keep measuring neutron stars to learn more!

Keep up with other exciting announcements about our universe by following NASA Universe on Twitter and Facebook.

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Rare & Record-Breaking Black Holes

While even the most “normal” black hole seems exotic compared to the tranquil objects in our solar system, there are some record-breaking oddballs. Tag along as we look at the biggest, closest, farthest, and even “spinniest” black holes discovered in the universe … that we know of right now!

Located 700 million light-years away in the galaxy Holmberg 15A, astronomers found a black hole that is a whopping 40 billion times the mass of the Sun — setting the record for the biggest black hole found so far. On the other hand, the smallest known black hole isn’t quite so easy to pinpoint. There are several black holes with masses around five times that of our Sun. There’s even one candidate with just two and a half times the Sun’s mass, but scientists aren’t sure whether it’s the smallest known black hole or actually the heaviest known neutron star!

You may need to take a seat for this one. The black hole GRS 1915+105 will make you dizzier than an afternoon at an amusement park, as it spins over 1,000 times per second! Maybe even more bizarre than how fast this black hole is spinning is what it means for a black hole to spin at all! What we're actually measuring is how strongly the black hole drags the space-time right outside its event horizon — the point where nothing can escape. Yikes!

If you’re from Earth, the closest black hole that we know of right now, Mon X-1 in the constellation Monoceros, is about 3,000 light-years away. But never fear — that’s still really far away! The farthest known black hole is J0313-1806. The light from its surroundings took a whopping 13 billion years to get to us! And with the universe constantly expanding, that distance continues to grow.

So, we know about large (supermassive, hundreds of thousands to billions of times the Sun's mass) and small (stellar-mass, five to dozens of times the Sun's mass) black holes, but what about other sizes? Though rare, astronomers have found a couple that seem to fit in between and call them intermediate-mass black holes. As for tiny ones, primordial black holes, there is a possibility that they were around when the universe got its start — but there’s not enough evidence so far to prove that they exist!

One thing that’s on astronomers’ wishlist is to see two supermassive black holes crashing into one another. Unfortunately, that event hasn’t been detected — yet! It could be only a matter of time before one reveals itself.

Though these are the records now, in early 2021 … records are meant to be broken, so who knows what we’ll find next!

Add some of these records and rare finds to your black hole-watch list, grab your handy-dandy black hole field guide to learn even more about them — and get to searching!

Keep up with NASA Universe on Facebook and Twitter where we post regularly about black holes.

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Black Holes: Seeing the Invisible!

Black holes are some of the most bizarre and fascinating objects in the cosmos. Astronomers want to study lots of them, but there’s one big problem – black holes are invisible! Since they don’t emit any light, it’s pretty tough to find them lurking in the inky void of space. Fortunately there are a few different ways we can “see” black holes indirectly by watching how they affect their surroundings.

Speedy stars

If you’ve spent some time stargazing, you know what a calm, peaceful place our universe can be. But did you know that a monster is hiding right in the heart of our Milky Way galaxy? Astronomers noticed stars zipping superfast around something we can’t see at the center of the galaxy, about 10 million miles per hour! The stars must be circling a supermassive black hole. No other object would have strong enough gravity to keep them from flying off into space.

Two astrophysicists won half of the Nobel Prize in Physics last year for revealing this dark secret. The black hole is truly monstrous, weighing about four million times as much as our Sun! And it seems our home galaxy is no exception – our Hubble Space Telescope has revealed that the hubs of most galaxies contain supermassive black holes.

Shadowy silhouettes

Technology has advanced enough that we’ve been able to spot one of these supermassive black holes in a nearby galaxy. In 2019, astronomers took the first-ever picture of a black hole in a galaxy called M87, which is about 55 million light-years away. They used an international network of radio telescopes called the Event Horizon Telescope.

In the image, we can see some light from hot gas surrounding a dark shape. While we still can’t see the black hole itself, we can see the “shadow” it casts on the bright backdrop.

Shattered stars

Black holes can come in a smaller variety, too. When a massive star runs out of the fuel it uses to shine, it collapses in on itself. These lightweight or “stellar-mass” black holes are only about 5-20 times as massive as the Sun. They’re scattered throughout the galaxy in the same places where we find stars, since that’s how they began their lives. Some of them started out with a companion star, and so far that’s been our best clue to find them.

Some black holes steal material from their companion star. As the material falls onto the black hole, it gets superhot and lights up in X-rays. The first confirmed black hole astronomers discovered, called Cygnus X-1, was found this way.

If a star comes too close to a supermassive black hole, the effect is even more dramatic! Instead of just siphoning material from the star like a smaller black hole would do, a supermassive black hole will completely tear the star apart into a stream of gas. This is called a tidal disruption event.

Making waves

But what if two companion stars both turn into black holes? They may eventually collide with each other to form a larger black hole, sending ripples through space-time – the fabric of the cosmos!

These ripples, called gravitational waves, travel across space at the speed of light. The waves that reach us are extremely weak because space-time is really stiff.

Three scientists received the 2017 Nobel Prize in Physics for using LIGO to observe gravitational waves that were sent out from colliding stellar-mass black holes. Though gravitational waves are hard to detect, they offer a way to find black holes without having to see any light.

We’re teaming up with the European Space Agency for a mission called LISA, which stands for Laser Interferometer Space Antenna. When it launches in the 2030s, it will detect gravitational waves from merging supermassive black holes – a likely sign of colliding galaxies!

Rogue black holes

So we have a few ways to find black holes by seeing stuff that’s close to them. But astronomers think there could be 100 million black holes roaming the galaxy solo. Fortunately, our Nancy Grace Roman Space Telescope will provide a way to “see” these isolated black holes, too.

Roman will find solitary black holes when they pass in front of more distant stars from our vantage point. The black hole’s gravity will warp the starlight in ways that reveal its presence. In some cases we can figure out a black hole’s mass and distance this way, and even estimate how fast it’s moving through the galaxy.

For more about black holes, check out these Tumblr posts!

⚫ Gobble Up These Black (Hole) Friday Deals!

⚫ Hubble’s 5 Weirdest Black Hole Discoveries

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Five Reasons You Wouldn’t Want to Live Near a Black Hole

Black holes are mystifying yet terrifying cosmic phenomena. Unfortunately, people have a lot of ideas about them that are more science fiction than science. Black holes are not cosmic vacuum cleaners, sucking up anything and everything nearby. But there are a few ways Hollywood has vastly underestimated how absolutely horrid black holes really are.

Black holes are superdense objects with a gravitational pull so strong that not even light can escape them. Scientists have overwhelming evidence for two types of black holes, stellar and supermassive, and see hints of an in-between size that’s more elusive. A black hole’s type depends on its mass (a stellar black hole is five to 30 times the mass of the Sun, while a supermassive black hole is 100,000 to billions of times the mass of the Sun), and can determine where we’re most likely to find them and how they formed. 

Let's focus on supermassive black holes for now, shall we? Supermassive black holes exist in the centers of most large galaxies. Some examples are Sagittarius A* (that’s pronounced “A-star”) at the center of our Milky Way and the black hole at the center of galaxy Messier 87, which became famous earlier this year when the Event Horizon Telescope released an image of it. As the name suggests, these black holes are — well — supermassive. Why are they so enormous? Scientists suspect it has something to do with their locations in the centers of galaxies. With so many stars and lots of gas there, they can grow large rapidly (astronomically speaking).

You may have seen a portrayal of planets around supermassive black holes in the movies. But what would the conditions on those worlds actually look like? What kinds of problems might you face?

1. 100% chance for cosmic winds

“Space weather” describes the changing conditions in space caused by stellar activity. Solar eruptions produce intense radiation and clouds of charged particles that sweep through our planetary system and can affect technology we rely on, damaging satellites and even causing electrical blackouts. Thankfully, Earth’s atmosphere and magnetic field protect us from most of the storms produced by the Sun.

Now, space weather near a black hole would be interesting if the black hole is consuming matter. It could be millions — perhaps even billions — of times stronger than the Sun’s, depending on how close the planet is. Even though black holes don’t emit light themselves, their surroundings can be very bright and hot. Accretion disks — swirling clouds of matter falling toward black holes — emit huge amounts of radiation and particles and form incredible magnetic fields. In them, you’d also have to worry about debris traveling at nearly the speed of light, slamming into your planet. It’d be hard to avoid getting hit by anything coming at you that fast!

2. Hello? Can you still hear us?

We launched the Parker Solar Probe to learn more about the Sun. If you lived on a world around a supermassive black hole, you'd probably want to study it too. But it would be a lot more challenging!

You’d have to launch satellites that could withstand the extreme space weather. And then there would be major communication issues — a time-delay in messages sent between the spacecraft and your planet.

On Earth we experience time gaps when talking to missions on Mars. It takes up to 22 minutes to hear back from them. Around a black hole, that effect would be much more extreme. Objects closer to the black hole would experience time differently, making things seem slower than they actually are. That means the delay in communications with a satellite launched toward a black hole would become longer and longer as it got closer and closer. By the time you hear back from your satellite, it might be gone!

3. Can someone turn off the lights?

Supermassive black holes at the centers of galaxies typically have a lot of nearby stars. In fact, if you were to live on a planet near the center of the Milky Way, there would be so many stars you could read at night without using electricity.

That sounds kind of cool, right? Maybe — unless your planet is actually orbiting the supermassive black hole. Being that close, the light from all those stars would be concentrated and amplified due to the extreme gravity around the black hole, making the light stronger and even causing scary beams of strong radiation. You would want to have a bucket of sunscreen ready to apply often — or simply never leave your home.

4. Did someone leave the oven on?

And not only would it be really bright, it would also be really toasty, thanks to radioactive heating! Those stars hanging around the black hole emit not just light but ghostly particles called neutrinos— speedy, tiny particles that weigh almost nothing and rarely interact with anything. While neutrinos coming from our Sun aren't enough to harm us, the volume that would be coming from the cluster of stars near a black hole would be enough to radioactively heat up whatever they slam into.

The planet would absorb neutrinos, which would, in turn, warm up the core of the planet eventually making it unbearably hot. It would be like living in a nuclear reactor. At least you’d be warm and could toss your winter coats?

5. You are what you eat?

If your planet got too close to a black hole, you’d likely face a gruesome fate. The forces from the black hole's gravity stretch matter, essentially turning it into a noodle. We call this spaghettification. (Beware the cosmic pasta-making machine?) Imagine yourself falling feet-first toward a black hole. Spaghettification happens because the gravity at your feet is sooooo much stronger than that at your head that you start to stretch out!

Maybe you wish you could simply drift around a black hole in a spacecraft and enjoy the view, or travel through one like science fiction depicts. Sadly, even if we had the means to get close to a black hole, it clearly wouldn’t be that simple or even very enjoyable.

Watch Dr. Jeremy Schnittman’s talk on the science behind the black hole from the movie Interstellar here.

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Hubble’s 5 Weirdest Black Hole Discoveries

Our Hubble Space Telescope has been exploring the wonders of the universe for nearly 30 years, answering some of our deepest cosmic questions. Some of Hubble’s most exciting observations have been about black holes — places in space where gravity pulls so much that not even light can escape. As if black holes weren’t wild enough already, Hubble has helped us make discoveries that show us they’re even weirder than we thought!

Supermassive Black Holes Are Everywhere

First, these things are all over the place. If you look at any random galaxy in the universe, chances are it has a giant black hole lurking in its heart. And when we say giant, we’re talking as massive as millions or even billions of stars! 

Hubble found that the mass of these black holes, hidden away in galactic cores, is linked to the mass of the host galaxy — the bigger the galaxy, the bigger the black hole. Scientists think this may mean that the black holes grew along with their galaxies, eating up some of the stuff nearby.

Some Star Clusters Have Black Holes

A globular cluster is a ball of old, very similar stars that are bound together by gravity. They’re fairly common — our galaxy has at least 150 of them — but Hubble has found some black sheep in the herd. Some of these clusters are way more massive than usual, have a wide variety of stars and may even harbor a black hole at the center. This suggests that at least some of the globular clusters in our galaxy may have once been dwarf galaxies that we absorbed.

Black Hole Jets Regulate Star Birth

While black holes themselves are invisible, sometimes they shoot out huge jets of energy as gas and dust fall into them. Since stars form from gas and dust, the jets affect star birth within the galaxy. 

Sometimes they get rid of the fuel needed to keep making new stars, but Hubble saw that it can also keep star formation going at a slow and steady rate.

Black Holes Growing in Colliding Galaxies

If you’ve ever spent some time stargazing, you know that staring up into a seemingly peaceful sea of stars can be very calming. But the truth is, it’s a hectic place out there in the cosmos! Entire galaxies — these colossal collections of gas, dust, and billions of stars with their planets — can merge together to form one supergalaxy. You might remember that most galaxies have a supermassive black hole at the center, so what happens to them when galaxies collide? 

In 2018, Hubble unveiled the best view yet of close pairs of giant black holes in the act of merging together to form mega black holes!

Gravitational Wave Kicks Monster Black Hole Out of Galactic Core

What better way to spice up black holes than by throwing gravitational waves into the mix! Gravitational waves are ripples in space-time that can be created when two massive objects orbit each other. 

In 2017, Hubble found a rogue black hole that is flying away from the center of its galaxy at over 1,300 miles per second (about 90 times faster than our Sun is traveling through the Milky Way). What booted the black hole out of the galaxy’s core? Gravitational waves! Scientists think that this is a case where two galaxies are in the late stages of merging together, which means their central black holes are probably merging too in a super chaotic process. 

Want to learn about more of the highlights of Hubble’s exploration? Check out this page! https://www.nasa.gov/content/goddard/2017/highlights-of-hubble-s-exploration-of-the-universe

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