A gaggle of black holes has been found clustered around the center of our home galaxy, the Milky Way—and the discovery hints at a much larger population of black holes hidden across the galaxy. The discover offers a new test bed for understanding the ripples in space-time known as gravitational waves.

For years, scientists have known that a monster black hole sits in the middle of the galaxy. Called Sagittarius A* (Sgr A*), the compact object is more than four million times as massive as our sun, but it's packed into a region of space no bigger than the distance between Earth and our star.

Scientists had long suspected that as many as 20,000 smaller black holes were orbiting the galactic center. But as the name suggests, black holes are not easy to see directly. (Find out how astronomers are trying to take the first picture of a black hole.)

Gravitational Waves 101 What are gravitational waves and how are they detected? These ripples in space-time, sometimes caused by neutron stars colliding, were recently recorded in the groundbreaking LIGO-Virgo observation.

To overcome this obstacle, a team of astronomers went looking for stellar binaries—specifically ones with black holes that are paired closely with stars. In these cases, matter from the star falls into its ultradense partner, and the swirling gas forms what's known as an accretion disk around the black hole's maw. This superheated disk of gas emits x-rays that astronomers can detect.

“They're just the tip of the iceberg,” says Chuck Hailey, an astrophysicist at the Columbia Astrophysics Lab and lead author of the study, published today in the journal Nature. “But the only way we could find these black holes is to look for these tracers.”

Thousands More?

The team then went looking for black hole binaries that are within about three light-years of Sgr A* and that are moving in ways that suggest they are falling into their supermassive cousin.

“Over a long period of time, you'd expect these black holes to rain down onto the supermassive black hole, where they get caught into orbit,” Hailey says.

Astronomers expect more black holes will be clustered around the massive galactic center than the number spread across the galaxy. So based on the new finds, the study authors think that as many as 500 black hole binaries exist in the Milky Way, and that the galaxy hosts up to ten thousand black holes in total.

They came to this conclusion by reasoning that the black holes with visible accretion disks are only a sampling of those that must exist.

“Imagine you were standing in a football field, and you had a whole pile of 100-watt lightbulbs and 10-watt lightbulbs,” Hailey says. Now, spread those bulbs out a mile away. “You could still see the 100-watt ones, but you might not see the 10-watt ones. By knowing what the ratio was in the football field, you could figure out how many dim ones you missed at a mile away.”

This conclusion relies on a theory that one out of every 20 black holes will latch on to a star. But Hailey says that even if the theory is not entirely accurate, it's likely the galaxy hosts many more black holes than the 60 or so we've seen so far.

“Let's suppose the theory is wrong, even by a factor of two or three,” he says. “We'll take it. If there's even a thousand of them there, that's spectacular, compared to not having found any.”

What Can Black Holes Teach Us?

The center of the Milky Way is the nearest supermassive black hole that scientists have to study, and the best laboratory for testing how objects crowded in space interact.

Hailey notes that the find also has implications for scientists studying gravitational waves, the ripples in space-time created by powerful cosmic events, like when massive objects collide. Knowing how many black holes are out there can help scientists studying gravitational waves predict which waves can be attributed to black holes and how they form.</s>WASHINGTON (Reuters) - Black holes are hanging out at the center of our galaxy by the thousands, according to scientists who have detected a bunch of them in the neighborhood of a supermassive black hole already known to reside at the heart of the Milky Way.

Researchers said data from the NASA’s orbiting Chandra X-ray Observatory allowed them to detect a dozen black holes surrounding Sagittarius A*, the mammoth black hole at the center of our spiral-shaped galaxy.

Black holes, which come in a variety of sizes, are extraordinarily dense entities with gravity so powerful that not even light can escape. Based on these findings, the scientists estimated that up to 10,000 black holes dwell within about 3 light years of Sagittarius A*.

“That’s a crowd,” Columbia University astrophysicist Chuck Hailey, lead author of the study published in the journal Nature, said on Thursday.

Sagittarius A*, boasting 4 million times the mass of our sun, is located 26,000 light years from Earth. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

The findings, which confirm decades-old predictions, provide insight into a fundamental aspect of galaxies.

“Since our galaxy is very average, it tells us that the universe is teeming with black holes orbiting near theirsupermassive black holes, because most galaxies have supermassive black holes,” Hailey said.

The newly detected black holes, all produced by the collapse of massive dying stars, are rare ones that captured and bound themselves to a passing star, forming what is called a stellar binary.

Black holes in isolation are hard to find, but the X-ray signatures of stellar binaries allowed their detection.

“Black holes can form farther out from the center of the galaxy. They gravitationally interact with stars, cosmic collisions so to speak, and lose energy,” Hailey said.

“As they lose energy, they sink to the center of the galaxy, the same way heavy sediment sinks faster than light sedimentin water. They get captured by the gravity of the supermassive black hole, catch a star, and voila, you have something we can see X-rays from.”

Supermassive black holes arise relatively soon after their galaxies are formed, devouring enormous amounts of gas, dust and stars to achieve colossal size. Hailey said, “As one black hole grows to such huge size, even if it was not originally in the exact center, it will sink into the center of the galaxy.”</s>A Columbia University-led team of astrophysicists has discovered a dozen black holes gathered around Sagittarius A* (Sgr A*), the supermassive black hole in the center of the Milky Way Galaxy. The finding is the first to support a decades-old prediction, opening up myriad opportunities to better understand the universe.

“Everything you’d ever want to learn about the way big black holes interact with little black holes, you can learn by studying this distribution,” said Columbia Astrophysicist Chuck Hailey, co-director of the Columbia Astrophysics Lab and lead author on the study. “The Milky Way is really the only galaxy we have where we can study how supermassive black holes interact with little ones because we simply can’t see their interactions in other galaxies. In a sense, this is the only laboratory we have to study this phenomenon.”

The study appears in the April 5 issue of Nature.

For more than two decades, researchers have searched unsuccessfully for evidence to support a theory that thousands of black holes surround supermassive black holes (SMBHs) at the center of large galaxies.

“There are only about five dozen known black holes in the entire galaxy — 100,000 light years wide — and there are supposed to be 10,000 to 20,000 of these things in a region just six light years wide that no one has been able to find,” Hailey said, adding that extensive fruitless searches have been made for black holes around Sgr A*, the closest SMBH to Earth and therefore the easiest to study. “There hasn’t been much credible evidence.”

He explained that Sgr A* is surrounded by a halo of gas and dust that provides the perfect breeding ground for the birth of massive stars, which live, die and could turn into black holes there. Additionally, black holes from outside the halo are believed to fall under the influence of the SMBH as they lose their energy, causing them to be pulled into the vicinity of the SMBH, where they are held captive by its force.

While most of the trapped black holes remain isolated, some capture and bind to a passing star, forming a stellar binary. Researchers believe there is a heavy concentration of these isolated and mated black holes in the Galactic Center, forming a density cusp which gets more crowded as distance to the SMBH decreases.

In the past, failed attempts to find evidence of such a cusp have focused on looking for the bright burst of X-ray glow that occurs when black holes mate with companion stars.

“It’s an obvious way to want to look for black holes,” Hailey said, “but the Galactic Center is so far away from Earth that those bursts are only strong and bright enough to see about once every 100 to 1,000 years.” To detect black hole binaries then, Hailey and his colleagues realized they would need to look for the fainter, but steadier X-rays emitted after the initial bonding, when the binaries are in an inactive state.

“It would be so easy if black hole binaries routinely gave off big bursts like neutron star binaries do, but they don’t, so we had to come up with another way to look for them,” Hailey said. “Isolated, unmated black holes are just black — they don’t do anything. So looking for isolated black holes is not a smart way to find them either. But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable. If we could find black holes that are coupled with low mass stars and we know what fraction of black holes will mate with low mass stars, we could scientifically infer the population of isolated black holes out there.”

Hailey and colleagues turned to archival data from the Chandra X-ray Observatory to test their technique. They searched for X-ray signatures of black hole-low mass binaries in their inactive state and were able to find 12 within three light years, of Sgr A*. The researchers then analyzed the properties and spatial distribution of the identified binary systems and extrapolated from their observations that there must be anywhere from 300 to 500 black hole-low mass binaries and about 10,000 isolated black holes in the area surrounding Sgr A*.

“This finding confirms a major theory and the implications are many,” Hailey said. “It is going to significantly advance gravitational wave research because knowing the number of black holes in the center of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them. All the information astrophysicists need is at the center of the galaxy.”

Hailey’s co-authors on the paper include: Kaya Mori, Michael E. Berkowitz, and Benjamin J. Hord, all of Columbia University; Franz E. Bauer, of the Instituto de Astrofísica, Facultad de Física, Pontificia, Universidad Católica de Chile, Millennium Institute of Astrophysics, Vicuña Mackenna, and the Space Science Institute; and Jaesub Hong, of Harvard-Smithsonian Center for Astrophysics.

Publication: Charles J. Hailey, et al., “A density cusp of quiescent X-ray binaries in the central parsec of the Galaxy,” Nature volume 556, pages 70–73 (05 April 2018) doi:10.1038/nature25029</s>At the centre of our galaxy lies a supermassive black hole, about four million times the mass of our sun. New research has found that it's not alone.

For some time, the theory has been that the supermassive black holes at the centre of most galaxies, including our own Milky Way, are accompanied by smaller black holes.

In a study published in Nature on Wednesday, a team of astronomers discovered 12 of these outliers, within three light-years of our supermassive black hole, called Sagittarius A*. The findings suggest that there are upwards of 10,000 surrounding the galactic centre.

But since black holes are black, with nothing — including light — able to escape their mighty grasp, how does one exactly go about finding them?

You can't see an inactive black hole, one that isn't consuming anything. But you can see evidence of a black hole's meal.

As black holes — the remnants of dead stars — gobble up matter, a particular type of X-ray is burped back out into the cosmos. These types of black holes are referred to as black hole binaries.

In an effort to spot some of these black hole binaries, the team analyzed data that had already been collected by the Chandra X-Ray Observatory in orbit around Earth.

"They're devilishly hard to find," Chuck Hailey, lead author of the paper and astrophysicist with Columbia University told CBC News.

"But every now and then you'll find one of these black holes catch a star, and matter will come out of this star in a disk around the black hole … so we can detect the tip of the iceberg."

They found a dozen of these black hole binaries, and because it's rare for a black hole to grab a star, the scientists can infer that many others are out there that didn't grab a star and are thus invisible.
• Supermassive black hole from early universe is farthest ever found

The astronomers were also careful not to be fooled by the many other intriguing X-ray-emitting objects at the galactic centre. Black holes consuming a dying star emit low-energy X-rays compared to other stars or objects, so they were able to isolate them omitting other, high-energy X-rays.

Black holes are one of the most fascinating objects in our universe. They form after the spectacular death of a massive star — about 10 times that of our own sun — a supernova explosion that can outshine the star's host galaxy.

As gravity takes over and eventually wins, it forms a singularity, a single point in space where gravity is so strong that no object — not even light — can escape its grasp once it crosses its boundary.

Supermassive black holes are believed to form at the same time a galaxy forms, though astronomers aren't certain of the exact process. It's believed that these types of black holes lie at the centre of most galaxies.

Stars form as gas and dust succumb to gravity and fusion is ignited. And it turns out the galactic centre is surrounded by a halo of gas and dust, a perfect breeding ground for massive stars needed to create black holes. These black holes eventually are believed to congregate around the centre.

"Some of these black holes were born billions of years ago," Hailey said. "Some of them were formed comparatively recently. So they kind of just collect there, it's sort of like a junkyard … they can't escape the pull from the supermassive black hole so they just kind of sit there."

What Hailey finds particularly exciting is that the new findings could also aid in more discoveries and the study of gravitational waves, first seen in 2015. Among other ways, these waves of gravity can be created by merging black holes.

Our galaxy is considered fairly normal, which means that gravitational wave theorists can can make predictions on how many gravitational wave events might happen in other galaxies. And, Hailey said, perhaps they will find one at the centre of a distant galaxy.

Overall, he's excited by the finding, particularly that it supports the decades-long prediction of these black holes. And he hopes that other astronomers will use publicly available data to further seek out these somewhat elusive mysteries of the universe.

"For me, you can kind of breathe a sigh of relief, that we really think we basically understand how things are happening at the centre of the galaxy."</s>A group of astrophysicists analysed a set of X-rays blasted from the centre of the galaxy in a hunt for black holes. With the help of NASA’s Chandra X-Ray Observatory, the scientists have found 12 black holes with masses similar to the stars surrounding the supermassive black hole Sagittarius A*. But the scientists have admitted the estimates are much graver, with as many as 20,000 black hole out there in the vast depths of deep space. The astounding black hole discovery comes hot on the heels of scientists announcing the Milky Way is expanding faster than the speed of sound.

Chuck Hailey, the study’s lead author and professor of physics at Columbia University, said finding black holes in space is an arduous task for astronomers. He said: “Isolated black holes just don’t do much that would lend themselves to easy detection. That’s why we say they are black. “Sure, they eat gas and dust, but they are very lousy at converting this fuel into X-rays, which we can detect. “But black holes with a stellar companion make X-rays. The star dumps gas into a disk around the black hole, and that disk is good at making X-rays.”

According to the published study, as many as 20,000 black holes are predicted to settle into the central parsec of the Galaxy as a result of the forces of dynamical friction. However at the moment a “density cusp”, or localised increase in number, indicating this presence has not yet been detected. Black holes, which are vast amounts of matter asked into small areas, are typically ten times larger than our own sun but packed into an area roughly the diameter of New York city. Although scientists cannot directly observe black holes with the technology we currently posses, they can detect black holes by studying the matter around them.

Astronomers believed a “supermassive” black hole sits at the centre of the Milky Way, called Sagittarius A*. Professor Hailey said: “The Milky Way is really the only galaxy we have where we can study how supermassive black holes interact with little ones because we simply can't see their interactions in other galaxies. “In a sense, this is the only laboratory we have to study this phenomenon." According to the expert there are only about five dizen known black holes in the entire galaxy, which spans an incredible width of 100,000 light years.</s>Scientists have long searched for proof of the decades-old theory that black holes surround the supermassive black hole known as Sagittarius A* that lies at the heart of our galaxy. By tweaking their approach just a little, astronomers have now turned up the first direct evidence that they do in fact exist, creating new opportunities to study the interplay between regular black holes and their much bigger brethren.

Sometimes when a black hole is sucked into and held in the vicinity of a supermassive black hole, they will latch onto a nearby star to form a stellar binary. This mating generates a big burst of X-ray light, which has provided black hole-hunters with a target to search for.

"It's an obvious way to want to look for black holes," explains Chuck Hailey, an astrophysicist at Columbia University and lead author on the new study. "But the Galactic Center is so far away from Earth that those bursts are only strong and bright enough to see about once every 100 to 1,000 years."

Hailey and his team found success by instead searching for the fainter but more consistent X-ray light beamed from the stellar binary after they've bonded, and are resting in an inactive state. They applied this technique to archival data gathered by NASA's Chandra X-ray Observatory, looking out for X-ray signatures of black hole-low mass binaries. They found 12 within three light years of Sagittarius A* that fit the bill nicely.

"It would be so easy if black hole binaries routinely gave off big bursts like neutron star binaries do, but they don't, so we had to come up with another way to look for them," Hailey said. "Isolated, unmated black holes are just black – they don't do anything. So looking for isolated black holes is not a smart way to find them either. But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable. If we could find black holes that are coupled with low mass stars and we know what fraction of black holes will mate with low mass stars, we could scientifically infer the population of isolated black holes out there."

By extrapolating their results in this way, making use of analysis and spatial distribution of already identified binary systems, they team figures there are between 300 and 500 black hole-low mass binaries in the same region, along with around 10,000 isolated black holes.

"Everything you'd ever want to learn about the way big black holes interact with little black holes, you can learn by studying this distribution," says Hailey. "The Milky Way is really the only galaxy we have where we can study how supermassive black holes interact with little ones because we simply can't see their interactions in other galaxies. In a sense, this is the only laboratory we have to study this phenomenon."</s>University of Columbia in New York reveals there could be 10,000 smaller black holes surrounding the supermassive black hole in the Milky Way's Galactic Center.

A new study by Columbia University suggests that 10,000 smaller black holes surround the supermassive black hole at the core of the Milky Way.

According to a report by Science Daily, researchers discovered a dozen black holes surrounding the supermassive black hole in the middle of the Milky Way, Sagittarius A. This supports predictions that smaller black holes surround a much larger black hole.

Chuck Hailey, the study’s lead author and a co-director of the university’s astrophysics lab, explains that studying the distribution makes it possible to learn the interaction between bigger black holes and the smaller black holes.

For years, scientists have been looking for evidence that much smaller black holes surround supermassive ones located at the core of large galaxies. The Columbia University study which appears in the April 5 issue of the journal Nature aims to shed light on this theory.

As Hailey explains, the most accessible place to prove this theory is by studying the closest supermassive black hole to Earth, Sagittarius A.

The most common method to look for black holes is to look for bursts of X-ray glow which occurs in some black hole binaries. According to Hailey, this is the obvious way to search for black holes located in the Galactic Center. However, bursts which are bright and strong enough can only be seen in 100 to 1,000 years. Hence, his team devised another method — looking for X-rays emitted by binaries that are in an inactive state. These emissions are fainter but steadier.

These emissions indicate the mating between a low mass star and a black hole, hence proving a more viable way of knowing what lies in the Galactic Center.

“Isolated, unmated black holes are just black — they don’t do anything. So looking for isolated black holes is not a smart way to find them either. But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable. If we could find black holes that are coupled with low mass stars and we know what fraction of black holes will mate with low mass stars, we could scientifically infer the population of isolated black holes out there.”

Based on the data from Chandra X-ray Observatory, the team tested the technique and searched for X-ray signatures indicating the fusion between a black hole and a low mass binary in an inactive state. Within three light years of the supermassive black hole, they found 12 black holes-low mass binaries.

The spatial distribution of the emissions they tracked indicates that there are about 300 to 500 black hole and low mass binaries and approximately 10,000 black holes in the area close to the Sagittarius A.

Discovering the existence of these 10,000 black holes surrounding the supermassive black hole Sagittarius A will be a valuable tool in the advancement of gravitation wave research and other studies involving the universe.</s>At the center of our galaxy is a massive black hole. This black hole, called Sagittarius A*, is approximately 6 million times the mass of our sun, and the gravitational field it generates is enough to keep our entire galaxy orbiting it. But Sagittarius A* is not the only black hole at the center of our galaxy: New research from Columbia University suggests that the galactic center could hold thousands more.

The Columbia researchers gathered data from NASA’s Chandra X-Ray Space Telescope, which studies the night sky looking for x-rays from stars, black holes, and other galaxies. In this case, the researchers looked at signals coming from a few light years around Sagittarius A*, hoping to find a handful of black holes nearby.

Black holes by themselves don’t tend to give off any x-rays, but when they’re orbiting around another star they do. In this case, the researchers managed to find a dozen such black holes with companion stars. Because nearly all black holes are loners, this suggests that there could be upwards of 10,000 total black holes in the center of our galaxy.

This new finding could help scientists looking to study black holes by giving them many more known black holes to study. Prior to this, scientists had only located a few dozen black holes in our entire galaxy. Perhaps this result could be the first in a series of new discoveries about these strange cosmic objects.</s>Artist's impression of a black hole that was formed by a star implosion. Using an X-ray telescope, astrophysicists detected a population of these at the Milky Way's centre.

Our galaxy's supermassive black hole's entourage of smaller black holes has been spotted for the first time.

Chuck Hailey from Columbia University and colleagues teased out the faint signal of a dozen "black hole binaries" — where a black hole and another object, such as a star, orbit each other — close to their supermassive counterpart in the centre of the Milky Way.

This cosmic posse, which could comprise more than 10,000 black holes in its entirety, was reported in Nature Astronomy today.

Black holes tend to come in two sizes. There are stellar-mass black holes — the super-dense remnant left when a star more than eight times the mass of the Sun dies.

But they have monster cousins.

These supermassive black holes, millions of times more massive than the Sun, are thought to be found in the centre of pretty much all large galaxies.

The Milky Way has one. It's about 4 million times the mass of the Sun and resides in the Sagittarius A* region. (The asterisk denotes the source of radio waves thought to be generated by the supermassive black hole.)

And where you find a supermassive black hole, astrophysicists predicted, you should also see clusters of stellar-mass black holes surrounding it, producing what's called a "density cusp".

While black holes can form quite far from the centre of their galaxies, they gradually lose energy and start to migrate towards the galactic centre, Professor Hailey said, "much as sediment dumped in water will sink down under the influence of gravity.

Another theory is that massive stars, born in gas and dust that surrounds a supermassive black hole, implode to form black holes.

Either way, our galaxy's supermassive black hole should be surrounded by hundreds of stellar-mass black holes — at least.

The problem has been spotting them.

So how do you 'see' a black hole?

One way to find the elusive objects is to look for bursts of X-rays that are produced when a black hole feeds off a companion star. The orbiting pair is called a black hole binary.

Despite telescopes being trained on the galactic centre for more than a decade, astrophysicists have had no joy.

So he and his colleagues decided not to seek these rare X-ray flashes.

Instead, they sniffed out the steady X-ray emissions expected from the disc of gas and dust that swirls around a black hole.

This was no easy feat. The centre of the Milky Way is around 25,000 light-years from Earth.

It's also crowded with other X-ray-emitting objects, such as binary pairs that contain a white dwarf star.

Their trick, Professor Hailey said, was to look for lower-energy X-rays — a signature of a black hole binary — in the midst of higher-energy X-rays, which are a hallmark of white dwarf binaries.

Using data collected by the Chandra X-ray Observatory telescope, they found 12 black hole binaries within around 3.3 light-years from Sagittarius A*.

This, Professor Hailey said, "is just the tip of the iceberg of all the black holes there".

Extrapolating from their distribution, he and his team calculated that there is probably hundreds of black hole binaries keeping Sagittarius A* company — and potentially more than 10,000 solo black holes.</s>For the last few years, Chuck Hailey has had the center of the Milky Way hanging in his office at Columbia University. The picture, pinned above his desk, shows a bright orange and yellow blob—the glow of cosmic gas as it gets devoured by the supermassive black hole at the center of the galaxy. Astronomers captured this glow using X-rays, a versatile type of radiation that’s good for seeing through galactic gas as well as human bodies. Some of the X-ray emissions astronomers detect coming from the galactic center come from this black hole, known as Sagittarius A*, but not all. The rest comes from a population of other, smaller black holes clustered in the region. Astronomers have long predicted the presence of such black holes at the center of the galaxy, which they said could number in the thousands. Now, Hailey and his colleagues have found the first evidence of these black holes. Using archival data from the Chandra X-ray Observatory, a telescope orbiting Earth, Hailey and his team at Columbia picked out 12 X-ray sources within a few light-years of the galactic center that they believe are some of these smaller black holes. Their research was published Wednesday in Nature.

The dozen black holes are small as far as black holes go, about 10 times the mass of our sun. They are infinitesimal, of course, compared to the supermassive black hole they surround, which is about 4 million times the mass of the sun. Here’s what Chandra captured (the blue dots are the newly discovered black holes): Courtesy of Nature and Hailey et al. Astronomers found the smaller black holes by looking for their victims. When a black hole orbits together with a star, in a formation known as a binary system, the black hole feeds on its companion, sucking the starlight into the shadows. The slow process of devouring the companion star produces a glowing disk of hot gas that can be seen by powerful telescopes through X-rays. This is why Hailey and his team were able to spot these black holes out of all the thousands out there. Without cannibalized stars to light the way, we can't see black holes with current technology “A black hole all by its lonesome doesn’t do much of anything, and even when it eats some gas or dust, it’s very inefficient at converting its food to X-rays or any other form of radiation,” Hailey says. “But when a black hole, or even a neutron star or a white dwarf, when they have a stellar companion—that is, a living star—that star will shed gas and form a disk around the black hole.” Those disks are very good at producing the X-rays detectable by powerful technology.

Hailey and his team predict there may be as many as 10,000 of these small black holes lurking in our galaxy’s center. They make this estimate based on astronomers’ observations of similar black holes with stellar companions closer to Earth—oh yeah, there are black holes floating around the entire Milky Way—and their X-ray emissions. If these black holes were in the galactic center, they’d be too dim for us to spot from here. “We’re seeing the tip of the iceberg,” Hailey said. “We’re actually missing most of them just because the center of the galaxy is so far away.” The new detection makes Hailey wonder just how many of these black holes are floating around without a star companion, completely invisible to our telescopes. It’s actually quite rare for a black hole to successfully lasso a star with its gravity and start chomping down on it, so there must be many more out there without a companion than with one, Hailey said. If the thought of thousands of black holes swirling about the center of your galaxy scares you, don’t worry. These mysterious objects are no threat to our little planet. But let’s say—just for fun—you found yourself at the galactic center, hurtling through the region alongside particles of cosmic dust. In that situation, it would actually be more advantageous to get swallowed up by the supermassive black hole instead of one of the smaller ones. Both would kill you, of course. But the bigger black hole would make the journey less painful, says Sera Markoff, an astrophysicist at the University of Amsterdam and a member of the Event Horizon Telescope, a project that’s striving to photograph a black hole for the first time. Every black hole is surrounded by an invisible boundary called the event horizon, beyond which nothing, not even light, can escape. Anything that crosses that horizon is a goner. If you were able to hover over the event horizon, extreme tidal forces—the fierce gravitational tug of the black hole—would stretch your body to resemble a strand of spaghetti. The smaller the black hole, the more concentrated the tidal forces, and the greater the tugging, Markoff said. “So the tidal force of a supermassive black hole is gentle”—relatively speaking, of course—“and when you pass through the event horizon, you wouldn’t really feel it. You wouldn’t get shredded until much further in,” she said. While the center of a galaxy would destroy any living creature that ended up there, from a cosmic perspective, it is a place of creation. Hailey likens it to a nursery for cultivating celestial objects. “It’s sort of like fertile soil in which to grow big stars, which then collapse into these black holes and then grab another star,” he said. This process produces the fertilizer for everything else in the universe, expelling the heavy elements that help seed new stars, planets and, in some lucky places, life.
A study published to the journal Nature finds dozens of potential stellar mass black holes in the Galactic Center, suggesting there may be as many as 20,000 orbiting the supermassive black hole Sagittarius A*.