# What is the smallest diameter black hole that can be formed naturally?

We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

I was watching the video I Put a 1mm Size Black Hole Next to Earth and This Happened - Universe Sandbox 2 discussing what would happen if a 1 millimeter black hole is orbiting the earth, and I began questioning myself, is it really possible to naturally have such a small black hole?

What is the smallest size that a black hole can form naturally in real life?

The mass at which a star is able to condense into a black hole upon its death is called the Tolman-Oppenheimer-Volkoff Limit, which is roughly 2.17 solar masses. At this mass, the Schwarzschild radius of the black hole (the size of its event horizon) is about 6410 meters by the equation

$$r_s = frac{2GM}{c^2}.$$

EDIT: I'd also like to add that the theoretical minimum mass for a black hole is the Planck mass, $$2.2 imes 10^{−8}$$ kg, which would yield a radius of $$3.267 imes 10^{-35}$$ meters, though these would not be formed by stellar collapse, though they could have formed as primordial black holes in the very early universe.

## What's the size of a black hole's central mass?

I understand that blackholes are measured usually by their event horizon diameter but what's the size of the central mass? I've read it's a singularity. Has it been proven to be a singularity or is a mathematical shortcut?

Singularity (infinity) is where the math goes, but we have no way of knowing if there's some as-yet undiscovered physics that kicks in to prevent that from happening. Infinities are usual a big red flag in physics that some portion of knowledge is missing. I remain agnostic on the matter, with a slight leaning towards the central object having dimensionality.

I don’t know if we will ever find out. It started with atoms that had mass and volume and we know they are squeezed immensely close together. Maybe a new state of matter is formed maybe it becomes pure gravity whatever that is. However, since the math breaks down we either have to find new math/physics or find out experimentally. We can’t see past the singularity so we are left with new math and/or physics.

Contracted blackholes? The Event Horizon, which is what the Street Slang term "black hole" is usually referring to, is the Schwarzschild Radius (it's just easier to remember Event Horizon than how Schwarzschild is spelled). This is what all the Photoshop images show, warping stars around a "black hole". This is another example of the damage to science and logic of extending this LSD popularized 1960's Street Slang term into the realm of science terminology. Everybody understands "black" and everybody knows what a "hole" is, so there are thousands and thousands of "theories" about "falling" into a hole. Everybody knows what its like to fall into a hole so "black holes" must be easy to understand (regardless this is called spaghettification by astrophysicists).

A singularity is a mathematical construct, not a physical description. A singularity literally means "one point" (the point of the point is the point). Anyway, it is Newtonian mechanics up to the Event Horizon boundary. Classical stellar "black holes" used to have a nuclear physics requirement of 2 to 3 Solar Masses to go supernova after running out of fuel, collapsing into itself. So, this is a star that is a few times larger than our Sun, after going through its functional stages, collapsing into an Event Horizon of a few kilometers diameter. The gravitational force mathematics is Newtonian to the Event Horizon diameter. Once the radius is within the Schwarzschild Radius, gravity is no longer defined as a force, per Einstein, and is a curvature of space-time.

The mass of the star that collapsed is still there. That is why it still exhibits gravitational force outside of the Event Horizon. Since there is no way to observe it or measure it, the math indicates it is a subatomic size, about the size of a neutron. It is only at the very center of this matter that the denominator goes to zero, making the resultant product infinite.

There are a lot of problems going on with all these descriptions of "black holes" going on. The first is the phrase "gravity so strong that light can't escape". The Classical Stellar "black hole" is a burned out star. There is no light because it has gone cold, there is no light being emitted in the first place, much less having a "need to escape". The problem with starting with this as a condition, i.e. a gravitational force/curvature "strong" enough to stop photon velocity creates a dyslexic reverse logic situation. Starting with the assumption the gravitational force/curvature is strong enough to "stop" light, then developing the equations to explain that process results in the gravity being all located at a center point, the singularity. It can be mathematically defined that way but there is still a physical mass there.

Otherwise, what all these "black hole" theories are saying is enough protons, neutrons, and electrons can be compressed so tightly that it turns into Nothing, no volume, no physical characteristics at all except intense gravitational curvature. This does not make rational sense.

In the undersea world of submarines, a diesel-electric submarine running on electric is called a "hole in the water". Submariners know this is just a slang sonar term and don't think the enemy submarine "disappeared". They know it is still there. Submariners can accept this interpretation of the word "hole" as being merely an expression, not analyzed endlessly as an actual hole.

## Black hole dubbed 'the Unicorn' may be galaxy's smallest one

Scientists have discovered what may be the smallest-known black hole in the Milky Way galaxy and the closest to our solar system - an object so curious that they nicknamed it 'the Unicorn.'

The researchers said the black hole is roughly three times the mass of our sun, testing the lower limits of size for these extraordinarily dense objects that possess gravitational pulls so strong not even light can escape. A luminous star called a red giant orbits with the black hole in a so-called binary star system named V723 Mon.

The black hole is located about 1,500 light years - the distance light travels in a year, 5.9 trillion miles (9.5 trillion km) - from Earth. While it may be the closest one to us, it is still far away. By way of comparison, the closest star to our solar system, Proxima Centauri, is 4 light years away.

Black holes like this one form when massive stars die and their cores collapse.

"We nicknamed this black hole 'the Unicorn' partly because V723 Mon is in the Monoceros constellation - which translates to unicorn - and partly because it is a very unique system" in terms of the black hole's mass and relative closeness to Earth, said Ohio State University astronomy doctoral student Tharindu Jayasinghe, lead author of the study published this week in the journal Monthly Notices of the Royal Astronomical Society.

There are three categories of black holes. The smallest, like 'the Unicorn,' are so-called stellar mass black holes formed by the gravitational collapse of a single star. There are gargantuan 'supermassive' black holes like the one at our galaxy's center, 26,000 light years from Earth, which is four million times the sun's mass. A few intermediate-mass black holes also have been found with masses somewhere in between.

"It is clear that nature makes black holes of a wide range of masses. But a three-solar-mass black hole is a big surprise. There are no very good models for how to make such a black hole, but I am sure people will work on that more now," said Ohio State University astronomy professor and study co-author Kris Stanek.

'The Unicorn' falls into what the researchers called a "mass gap" between the largest-known neutron stars - objects similarly formed by a large star's collapse - at around 2.2 times the mass of our sun and what previously had been considered the smallest black holes at around five times the sun's mass.

"'The unicorn' is truly one of the smallest black holes possible," Jayasinghe said.

Its strong gravity alters the shape of its companion star in a phenomenon known as tidal distortion, making it elongated rather than spherical and causing its light to change as it moves along its orbital path. It was these effects on the companion star, observed using Earth-based and orbiting telescopes, that indicated the black hole's presence.

"Black holes are electromagnetically dark, and so they are difficult to find," Jayasinghe said.

Unlike some other black holes orbiting with a star, this one was not observed to be drawing material from its companion, which is 173 times more luminous than our sun.

The only smaller potential black hole is one with a mass 2.6 times that of our sun that was spotted in another galaxy, Jayasinghe said.

Another team of scientists last year described a black hole roughly 1,000 light years from Earth, but other researchers have questioned whether it is a black hole.

## Smallest Black Hole Found

NASAscientists have identified the smallest, lightest black hole yet found.

The newlightweight record-holder weighs in at about 3.8 times the mass of our sun andis only 15 miles (24 kilometers) in diameter.

"Thisblack hole is really pushing the limits," said study team leader NikolaiShaposhnikov of NASA's Goddard Space Flight Center in Greenbelt, Md. "Formany years astronomers have wanted to know the smallest possible size of ablack hole, and this little guy is a big step toward answering thatquestion."

Thelow-mass blackhole sits in a binary system in our galaxy known as XTE J1650-500 in thesouthern hemisphere constellation Ara. NASA's Rossi X-ray Timing Explorer(RXTE) satellite discovered the system in 2001, and astronomers soon realizedthat the system harbored a relatively lightweight black hole. But the blackhole's mass had never been precisely measured.

Black holescan't be seen, but they're identified by the activity around them, which alsohelps astronomers estimate a size of the region inside the activity, and howmuch mass must be in that confined region to generate all the surroundingactivity. More specifically, astronomers can weigh black holes by using arelationship between the apparent size of the black hole and the X-rays emittedby the torrent of gas that swirls into the black hole's disk from its companionstar.

As the gaspiles up near the black hole, it "becomes very dense and congested,"like a traffic jam, Shaposhnikov said at a press conference announcing thefind. "So matter has to literally squeeze into the black hole."

As it issqueezed, the gas heats up and radiates X-rays. The intensity of the X-raysvaries in a pattern repeated over a nearly regular interval. Astronomers havelong suspected that the frequency of this signal, called the quasi-periodicoscillation, or QPO, depends on the mass of the black hole.

As theblack hole gets bigger, the zone of swirling gas is pushed farther out, so theQPO ticks away slowly. But for smaller black holes, the gas sits closer in andthe QPO ticks rapidly.

Shaposhnikovand his colleague Lev Titarchuk of George Mason University used this methodto "weigh" XTE J1650-500 and found a mass of 3.8 suns. This valueis well below the previous record holder GRO 1655-40, which tips the scales atabout 6.3 suns.

This new ?massmeasurement could help shed light on what the smallest star that will produce ablack hole is. Astronomers know that some unknown critical threshold, possiblybetween 1.7 and 2.7 solar masses, marks the boundary between a star that generatesa black hole upon its death and one that produces a neutron star.

"Thisnew result brings us much closer to the theoretically predicted limit,"Shaposhnikov said.

Knowingthis boundary would help scientists understand the behavior of matter when itis scrunched to extraordinarily high densities.

"Thequestion of black hole masses has concerned us for more than a decade now,"said astrophysicist Vicky Kalogera of Northwestern University, who was notinvolved with the study, during the press conference. Scientists had predictedthat there should be more black holes at the lower end of the mass range thanastronomers had identified, so this study helps clear up some confusion as towhere these lightweight black holes were, she added.

Kalogeradid caution that the method used by Shaposhnikov and Titarchuk is not the mainway that black hole masses are measured, but noted that their measurements ofthe masses of other black holes agreed well with the results from the standardmethod.

Shaposhnikovand Titarchuk presented their findings on March 31 at the American AstronomicalSociety's High-Energy Astrophysics Division meeting in Los Angeles.

## A black hole dubbed ‘the Unicorn’ may be galaxy’s smallest one

WASHINGTON (Reuters) – Scientists have discovered what may be the smallest-known black hole in the Milky Way galaxy and the closest to our solar system – an object so curious that they nicknamed it ‘the Unicorn.’

The researchers said the black hole is roughly three times the mass of our sun, testing the lower limits of size for these extraordinarily dense objects that possess gravitational pulls so strong not even light can escape. A luminous star called a red giant orbits with the black hole in a so-called binary star system named V723 Mon.

The black hole is located about 1,500 light years – the distance light travels in a year, 5.9 trillion miles (9.5 trillion km) – from Earth. While it may be the closest one to us, it is still far away. By way of comparison, the closest star to our solar system, Proxima Centauri, is 4 light years away.

Black holes like this one form when massive stars die and their cores collapse.

“We nicknamed this black hole ‘the Unicorn’ partly because V723 Mon is in the Monoceros constellation – which translates to unicorn – and partly because it is a very unique system” in terms of the black hole’s mass and relative closeness to Earth, said Ohio State University astronomy doctoral student Tharindu Jayasinghe, lead author of the study published this week in the journal Monthly Notices of the Royal Astronomical Society.

There are three categories of black holes. The smallest, like ‘the Unicorn,’ are so-called stellar mass black holes formed by the gravitational collapse of a single star. There are gargantuan ‘supermassive’ black holes like the one at our galaxy’s center, 26,000 light years from Earth, which is four million times the sun’s mass. A few intermediate-mass black holes also have been found with masses somewhere in between.

“It is clear that nature makes black holes of a wide range of masses. But a three-solar-mass black hole is a big surprise. There are no very good models for how to make such a black hole, but I am sure people will work on that more now,” said Ohio State University astronomy professor and study co-author Kris Stanek.

‘The Unicorn’ falls into what the researchers called a “mass gap” between the largest-known neutron stars – objects similarly formed by a large star’s collapse – at around 2.2 times the mass of our sun and what previously had been considered the smallest black holes at around five times the sun’s mass.

“‘The unicorn’ is truly one of the smallest black holes possible,” Jayasinghe said.

Its strong gravity alters the shape of its companion star in a phenomenon known as tidal distortion, making it elongated rather than spherical and causing its light to change as it moves along its orbital path. It was these effects on the companion star, observed using Earth-based and orbiting telescopes, that indicated the black hole’s presence.

“Black holes are electromagnetically dark, and so they are difficult to find,” Jayasinghe said.

Unlike some other black holes orbiting with a star, this one was not observed to be drawing material from its companion, which is 173 times more luminous than our sun.

The only smaller potential black hole is one with a mass 2.6 times that of our sun that was spotted in another galaxy, Jayasinghe said.

Another team of scientists last year described a black hole roughly 1,000 light years from Earth, but other researchers have questioned whether it is a black hole.

## Smallest Known Galaxy with a Supermassive Black Hole

University of Utah astronomer Anil Seth will deliver a public lecture about tiny galaxies and big black holes at 7 p.m. MDT Saturday, Sept. 20, 2014, at the Clark Planetarium’s ATK IMAX Theater in downtown Salt Lake City. Tickets are \$2 for the general public on first-come basis.

Sept. 17, 2014 – A University of Utah astronomer and his colleagues discovered that an ultracompact dwarf galaxy harbors a supermassive black hole – the smallest galaxy known to contain such a massive light-sucking object. The finding suggests huge black holes may be more common than previously believed.

“It is the smallest and lightest object that we know of that has a supermassive black hole,” says Anil Seth, lead author of an international study of the dwarf galaxy published in Thursday’s issue of the journal Nature. “It’s also one of the most black hole-dominated galaxies known.”

The astronomers used the Gemini North 8-meter optical-and-infrared telescope on Hawaii’s Mauna Kea and photos taken by the Hubble Space Telescope to discover that a small galaxy named M60-UCD1 has a black hole with a mass equal to 21 million suns.

Their finding suggests plenty of other ultracompact dwarf galaxies likely also contain supermassive black holes – and those dwarfs may be the stripped remnants of larger galaxies that were torn apart during collisions with yet other galaxies.

“We don’t know of any other way you could make a black hole so big in an object this small,” says Seth, an assistant professor of physics and astronomy at the University of Utah. “There are a lot of similar ultracompact dwarf galaxies, and together they may contain as many supermassive black holes as there are at the centers of normal galaxies.”

Black holes are collapsed stars and collections of stars with such strong gravity that even light is pulled into them, although material around them sometimes can spew jets of X-rays and other forms of radiation. Supermassive black holes – those with the mass of at least 1 million stars like our sun – are thought to be at the centers of many galaxies.

The central, supermassive black hole at the center of our Milky Way galaxy has the mass of 4 million suns, but as heavy as that is, it is less than 0.01 percent of the galaxy’s total mass, estimated at some 50 billion solar masses.

By comparison, the supermassive black hole at the center of ultracompact dwarf galaxy M60-UCD1 is five times larger than the Milky Way’s, with a mass of 21 million suns, and is a stunning 15 percent of the small galaxy’s total mass of 140 million suns.

“That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1,” Seth says.

“We believe this once was a very big galaxy with maybe 10 billion stars in it, but then it passed very close to the center of an even larger galaxy, M60, and in that process all the stars and dark matter in the outer part of the galaxy got torn away and became part of M60,” he says. “That was maybe as much as 10 billion years ago. We don’t know.”

Seth says ultracompact dwarf galaxy M60-UCD1 may be doomed, although he cannot say when because the dwarf galaxy’s orbit around M60 isn’t known. M60 is among the largest galaxies in what astronomers refer to as “the local universe.”

“Eventually, this thing may merge with the center of M60, which has a monster black hole in it, with 4.5 billion solar masses – more than 1,000 times bigger than the supermassive black hole in our galaxy. When that happens, the black hole we found in M60-UCD1 will merge with that monster black hole.”

Galaxy M60 also is pulling in another galaxy, named NGC4647. M60 is about 25 times more massive than NGC4647.

Ultracompact Dwarf Galaxies and Supermassive Black Holes

The study – conducted by Seth and 13 other astronomers – was funded by the National Science Foundation in the U.S., the German Research Foundation and the Gemini Observatory partnership, which includes the NSF and scientific agencies in Canada, Chile, Australia, Brazil and Argentina.

Ultracompact dwarf galaxies are among the densest star systems in the universe. M60-UCD1 is the most massive of these systems now known, with a total of 140 million solar masses.

These dwarf galaxies range are less than a few hundred light years across (about 1,700 trillion miles wide), compared with our Milky Way’s 100,000-light-year diameter.

M60-UCD1 is roughly 54 million light years from Earth or about 320 billion billion miles. But the dwarf galaxy is only 22,000 light years from the center of galaxy M60, which “is closer than the sun is to the center of the Milky Way,” Seth says.

Astronomers have debated whether these dwarf galaxies are the stripped centers or nuclei of larger galaxies that were ripped away during collisions with other galaxies, or whether they formed like globular clusters – groups of perhaps 100,000 stars, all born together. There are about 200 globular clusters in our Milky Way, and some galaxies have thousands, Seth says.

The astronomers estimated the mass of the dwarf galaxy’s supermassive black hole by using the Gemini North telescope to measure the speed and motion of stars in orbit around it, and they showed the galaxy contains more mass than would be expected by the amount of starlight it emits. The stars at the center of M60-UCD1 move at about 230,000 mph – faster than stars would be expected to move without the black hole.

An alternate theory is that M60-UCD1 doesn’t have a supermassive black hole, but instead is populated by a lot of massive, dim stars.

But Seth says the research team’s observations with the Gemini North telescope and analysis of archival photos by the Hubble Space Telescope revealed that mass was concentrated in the galaxy’s center, indicating the presence of a supermassive black hole. That suggests that M60-UCD1 is the stripped nucleus of what once was a much larger galaxy, and that other ultracompact dwarf galaxies also may harbor huge black holes, Seth says.

The galaxy that was stripped and left M60-UCD1 as a remnant was about 10 billion solar masses, or about one-fifth the mass of the Milky Way, Seth says.

The astronomers studied M60-UCD1 because they had published a paper last year showing the galaxy was an X-ray source and was extremely dense. The X-ray emissions suggest gas is being sucked into the black hole at a rate typical of supermassive black holes in much larger galaxies.

The Research Facilities and Team

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes: Gemini North on the island of Hawaii and Gemini South on Cerro Pachón in central Chile. Together, the telescopes cover both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin and actively controlled mirrors to collect and focus infrared light from space, eliminating the blurring effects of the atmosphere and enabling the observations for the new study. The observatory is managed by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation.

The Hubble Space Telescope was built by NASA and the European Space Agency and is operated by the Space Telescope Science Institute.

Seth conducted the study with University of Utah physics and astronomy postdoctoral researcher Mark den Brok and with astronomers Remco van den Bosch of the Max Planck Institute for Astronomy, Germany Steffen Mieske of the European Southern Observatory, Santiago, Chile Holger Baumgardt of the University of Queensland, Australia Jay Strader of Michigan State University Nadine Neumayer and Michel Hilker of the European Southern Observatory, Garching, Germany Igor Chilingarian of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and Moscow State University Richard McDermid and Lee Spitler of Asutralia’s Macquarie University Jean Brodie of the University of California, Santa Cruz Matthias J. Frank of the University of Heidelberg, Germany and Jonelle Walsh of the University of Texas, Austin.

A video simulation of galaxy M60’s gravity stripping M60-UCD1’s outer parts is here: http://vimeo.com/105370891
Until the embargo expires, media may use the case-sensitive password: Baumgardt

Caption and credit for video:

Formation of Dwarf Galaxy M60-UCD1: University of Utah astronomer Anil Seth led an international research team that discovered the smallest galaxy known to harbor a supermassive black hole. The video simulation shows how this small galaxy, named M60-UCD1, was formed from a larger, normal galaxy. The video begins with a background image made by the Hubble Space Telescope, with the huge elliptical galaxy M60 in the center, galaxy NGC4647 in the upper right and MC60-UCD as a small whitish spot lower right. As the video begins, a normal galaxy (yellow and red) orbits M60. During an estimated 500 million years, M60’s gravity strips stars (red material) from the orbiting galaxy, leaving as a remnant the ultracompact dwarf galaxy now known as M60-UCD1. The end of the video zooms in on the Hubble Space Telescope close-up image of M60-UCD1, which today continues to orbit M60. Seth says that while this process took about 500 million years, astronomers don’t know when it happened, and that it could have been billions of years ago. This video was made by University of Queensland astronomer Holger Baumgardt, one of Seth’s co-authors on the new study published by Nature.

## How big is a mini black hole?

Yesterday at the American Astronomical Society's conference in Los Angeles, evidence for the smallest black hole ever observed was presented. It comes in at a mere 3.8 times the Sun's mass and is only 24 kilometers across. New Scientist has a story about it.

Also Know, what is the smallest black hole discovered? The Smallest Known Black Hole. NASA scientists have identified the lightest black hole yet, just 3.8 times the mass of the sun, in a binary star system in the Milky Way known as XTE J1650-500. The next smallest black hole, spotted in 1994, weighed in at 6.3 solar masses.

People also ask, how big is a miniature black hole?

NASAscientists have identified the smallest, lightest black hole yet found. The newlightweight record-holder weighs in at about 3.8 times the mass of our sun andis only 15 miles (24 kilometers) in diameter.

The black hole would then lose the rest of its mass in a short amount of time as abrupt explosions&mdashwe can detect these explosions as gamma ray bursts. The end. So, yes, black holes do die, and they do so when the theories of the extremely large come together with the theories of the very small.

## How to watch June’s ‘strawberry’ moon this Thursday

Scientists have discovered what may be the smallest-known black hole in the Milky Way galaxy and the closest to our solar system – an object so curious that they nicknamed it ‘the Unicorn.’

The researchers said the black hole is roughly three times the mass of our sun, testing the lower limits of size for these extraordinarily dense objects that possess gravitational pulls so strong not even light can escape. A luminous star called a red giant orbits with the black hole in a so-called binary star system named V723 Mon.

The black hole is located about 1,500 light years – the distance light travels in a year, 5.9 trillion miles (9.5 trillion km) – from Earth. While it may be the closest one to us, it is still far away. By way of comparison, the closest star to our solar system, Proxima Centauri, is 4 light years away.

Black holes like this one form when massive stars die and their cores collapse.

“We nicknamed this black hole ‘the Unicorn’ partly because V723 Mon is in the Monoceros constellation – which translates to unicorn – and partly because it is a very unique system” in terms of the black hole’s mass and relative closeness to Earth, said Ohio State University astronomy doctoral student Tharindu Jayasinghe, lead author of the study published this week in the journal Monthly Notices of the Royal Astronomical Society.

There are three categories of black holes. The smallest, like ‘the Unicorn,’ are so-called stellar mass black holes formed by the gravitational collapse of a single star. There are gargantuan ‘supermassive’ black holes like the one at our galaxy’s center, 26,000 light years from Earth, which is four million times the sun’s mass. A few intermediate-mass black holes also have been found with masses somewhere in between.

“It is clear that nature makes black holes of a wide range of masses. But a three-solar-mass black hole is a big surprise. There are no very good models for how to make such a black hole, but I am sure people will work on that more now,” said Ohio State University astronomy professor and study co-author Kris Stanek.

‘The Unicorn’ falls into what the researchers called a “mass gap” between the largest-known neutron stars – objects similarly formed by a large star’s collapse – at around 2.2 times the mass of our sun and what previously had been considered the smallest black holes at around five times the sun’s mass.

“‘The unicorn’ is truly one of the smallest black holes possible,” Jayasinghe said.

Its strong gravity alters the shape of its companion star in a phenomenon known as tidal distortion, making it elongated rather than spherical and causing its light to change as it moves along its orbital path. It was these effects on the companion star, observed using Earth-based and orbiting telescopes, that indicated the black hole’s presence.

“Black holes are electromagnetically dark and so they are difficult to find,” Jayasinghe said.

Unlike some other black holes orbiting with a star, this one was not observed to be drawing material from its companion, which is 173 times more luminous than our sun.

The only smaller potential black hole is one with a mass 2.6 times that of our sun that was spotted in another galaxy, Jayasinghe said.

Another team of scientists last year described a black hole roughly 1,000 light-years from Earth, but other researchers have questioned whether it is a black hole.

Scientists have discovered what may be the smallest-known black hole in the Milky Way galaxy and the closest to our solar system — an object so curious that they nicknamed it 'the Unicorn.'

The researchers said the black hole is roughly three times the mass of our sun, testing the lower limits of size for these extraordinarily dense objects that possess gravitational pulls so strong not even light can escape. A luminous star called a red giant orbits with the black hole in a so-called binary star system named V723 Mon.

The black hole is located about 1,500 light years — the distance light travels in a year, 9.5 trillion km — from Earth. While it may be the closest one to us, it is still far away. By way of comparison, the closest star to our solar system, Proxima Centauri, is 4 light years away.

Detecting the unified call of black holes and stars

Black holes like this one form when massive stars die and their cores collapse.

"We nicknamed this black hole 'the Unicorn' partly because V723 Mon is in the Monoceros constellation — which translates to unicorn — and partly because it is a very unique system" in terms of the black hole's mass and relative closeness to Earth, said Ohio State University astronomy doctoral student Tharindu Jayasinghe, lead author of the study published this week in the journal Monthly Notices of the Royal Astronomical Society.

There are three categories of black holes:

1. The smallest, like 'the Unicorn,' are so-called stellar mass black holes formed by the gravitational collapse of a single star.
2. There are gargantuan 'supermassive' black holes like the one at our galaxy's center, 26,000 light years from Earth, which is four million times the sun's mass.
3. A few intermediate-mass black holes also have been found with masses somewhere in between.

"It is clear that nature makes black holes of a wide range of masses. But a three-solar-mass black hole is a big surprise. There are no very good models for how to make such a black hole, but I am sure people will work on that more now," said Ohio State University astronomy professor and study co-author Kris Stanek.

'The Unicorn' falls into what the researchers called a "mass gap" between the largest-known neutron stars - objects similarly formed by a large star's collapse - at around 2.2 times the mass of our sun and what previously had been considered the smallest black holes at around five times the sun's mass.

Astronomers sight wandering huge black hole, but at a safe distance

"'The unicorn' is truly one of the smallest black holes possible," Jayasinghe said.

Its strong gravity alters the shape of its companion star in a phenomenon known as tidal distortion, making it elongated rather than spherical and causing its light to change as it moves along its orbital path. It was these effects on the companion star, observed using Earth-based and orbiting telescopes, that indicated the black hole's presence.

"Black holes are electromagnetically dark, and so they are difficult to find," Jayasinghe said.

Unlike some other black holes orbiting with a star, this one was not observed to be drawing material from its companion, which is 173 times more luminous than our sun. The only smaller potential black hole is one with a mass 2.6 times that of our sun that was spotted in another galaxy, Jayasinghe said.

## A black hole dubbed ‘the Unicorn’ may be galaxy’s smallest one

WASHINGTON (Reuters) – Scientists have discovered what may be the smallest-known black hole in the Milky Way galaxy and the closest to our solar system – an object so curious that they nicknamed it ‘the Unicorn.’

The researchers said the black hole is roughly three times the mass of our sun, testing the lower limits of size for these extraordinarily dense objects that possess gravitational pulls so strong not even light can escape. A luminous star called a red giant orbits with the black hole in a so-called binary star system named V723 Mon.

The black hole is located about 1,500 light years – the distance light travels in a year, 5.9 trillion miles (9.5 trillion km) – from Earth. While it may be the closest one to us, it is still far away. By way of comparison, the closest star to our solar system, Proxima Centauri, is 4 light years away.

Black holes like this one form when massive stars die and their cores collapse.

“We nicknamed this black hole ‘the Unicorn’ partly because V723 Mon is in the Monoceros constellation – which translates to unicorn – and partly because it is a very unique system” in terms of the black hole’s mass and relative closeness to Earth, said Ohio State University astronomy doctoral student Tharindu Jayasinghe, lead author of the study published this week in the journal Monthly Notices of the Royal Astronomical Society.

There are three categories of black holes. The smallest, like ‘the Unicorn,’ are so-called stellar mass black holes formed by the gravitational collapse of a single star. There are gargantuan ‘supermassive’ black holes like the one at our galaxy’s center, 26,000 light years from Earth, which is four million times the sun’s mass. A few intermediate-mass black holes also have been found with masses somewhere in between.

“It is clear that nature makes black holes of a wide range of masses. But a three-solar-mass black hole is a big surprise. There are no very good models for how to make such a black hole, but I am sure people will work on that more now,” said Ohio State University astronomy professor and study co-author Kris Stanek.

‘The Unicorn’ falls into what the researchers called a “mass gap” between the largest-known neutron stars – objects similarly formed by a large star’s collapse – at around 2.2 times the mass of our sun and what previously had been considered the smallest black holes at around five times the sun’s mass.

“‘The unicorn’ is truly one of the smallest black holes possible,” Jayasinghe said.

Its strong gravity alters the shape of its companion star in a phenomenon known as tidal distortion, making it elongated rather than spherical and causing its light to change as it moves along its orbital path. It was these effects on the companion star, observed using Earth-based and orbiting telescopes, that indicated the black hole’s presence.

“Black holes are electromagnetically dark, and so they are difficult to find,” Jayasinghe said.

Unlike some other black holes orbiting with a star, this one was not observed to be drawing material from its companion, which is 173 times more luminous than our sun.

The only smaller potential black hole is one with a mass 2.6 times that of our sun that was spotted in another galaxy, Jayasinghe said.

Another team of scientists last year described a black hole roughly 1,000 light years from Earth, but other researchers have questioned whether it is a black hole.