‘Black hole police’ discover first dormant black hole outside the Milky Way

‘Black hole police’ discover first dormant black hole outside the Milky Way

A dormant black hole at least nine times the mass of the Sun has been discovered just 160,000 light-years from Earth, orbiting a star.

A team of researchers – known as the ‘black hole police’ because they have debunked so many black hole discoveries – searched nearly 1,000 stars from the Tarantula Nebula in the constellation Dorado before the locate.

They claim it is the first dormant “stellar mass” black hole to be detected outside the Milky Way galaxy.

Stellar-mass black holes form when massive stars reach the end of their lives and collapse under their own gravity.

The black hole is said to be “dormant” if it is not actively devouring matter and, therefore, emitting no light or other radiation.

The discovery has been compared to finding a “needle in a haystack”, as dormant black holes are notoriously difficult to spot because they don’t interact with their surroundings.

Co-author Dr Pablo Marchant of KU Leuven in Belgium said: “It’s amazing, we hardly know of any dormant black holes given how astronomers think of them.”

Artist's impression of the binary system VFTS 243. The system, which is located in the Tarantula Nebula in the Large Magellanic Cloud, is composed of a hot blue star with 25 times the mass of the Sun and a black hole , which is at least nine times the mass of the Sun

Artist’s impression of the binary system VFTS 243. The system, which is located in the Tarantula Nebula in the Large Magellanic Cloud, is composed of a hot blue star with 25 times the mass of the Sun and a black hole , which is at least nine times the mass of the Sun

Artist's impression of the VFTS 243 binary system. The background image shows a VISTA (Visible and Infrared Survey Telescope for Astronomy) image of a segment of the Large Magellanic Cloud, marking the region in which VFTS 243 resides.  Sizes of star, black hole and orbits are not to scale

Artist’s impression of the VFTS 243 binary system. The background image shows a VISTA (Visible and Infrared Survey Telescope for Astronomy) image of a segment of the Large Magellanic Cloud, marking the region in which VFTS 243 resides. Sizes of star, black hole and orbits are not to scale

WHAT IS A “BINARY SYSTEM”?

A binary star is a system of two stars bound by gravity and orbiting each other.

Either star in the system could be a black hole.

When they do, they are often identified by the presence of bright X-ray emissions.

X-rays are produced by matter falling from one component, called the donor (usually a relatively normal star), to the other component, called the accretor (the black hole).

Matter forms a glowing accretion disk swirling around the black hole.

However, observations from NASA’s Chandra X-ray Telescope reveal that VFTS 243 is weak in X-rays.

The newly discovered black hole is in the Large Magellanic Cloud, a neighboring satellite galaxy to the Milky Way.

The Large Magellanic Cloud orbits a hot blue star nearly three times the size of our galaxy.

Thousands of stellar-mass black holes are thought to exist in the Milky Way and Magellanic Clouds.

They are much smaller than the supermassive black hole 27,000 light-years from Earth that powers the Milky Way, known as Sagittarius A*.

The black hole is part of a “binary” with a bright companion star, where they orbit each other in a system known as VFTS 243.

Co-author Dr Julia Bodensteiner, from the European Southern Observatory (ESO) in Germany, said: ‘For more than two years we have been looking for such binary black hole systems.

“I was very excited when I heard about VFTS 243, which I believe is the most compelling candidate reported to date.”

It took six years of data from ESO’s Very Large Telescope (VLT) to officially identify VFTS 243.

The VLT’s FLAMES (Fibre Large Array Multi Element Spectrograph) scanner can observe more than a hundred objects at a time.

Historically, binaries hosting stellar-mass black holes have been identified through the presence of bright X-ray emissions from the accretion disk.

The glowing accretion disk is formed from gases from the atmosphere of the living star that flow towards and surround the black hole.

However, observations from NASA’s Chandra X-ray Telescope reveal that VFTS 243 is weak in X-rays.

This image from the VLT Survey Telescope at ESO's Paranal Observatory in Chile shows the Tarantula Nebula and its surroundings in the Large Magellanic Cloud.  It shows star clusters, clouds of glowing gas and the scattered remnants of supernova explosions

This image from the VLT Survey Telescope at ESO’s Paranal Observatory in Chile shows the Tarantula Nebula and its surroundings in the Large Magellanic Cloud. It shows star clusters, clouds of glowing gas and the scattered remnants of supernova explosions

Historically, binaries hosting stellar-mass black holes have been identified through the presence of bright X-ray emissions from the accretion disk (pictured).  The glowing accretion disk is formed by gases from the living star's atmosphere flowing towards and surrounding the black hole (stock illustration)

Historically, binaries hosting stellar-mass black holes have been identified through the presence of bright X-ray emissions from the accretion disk (pictured). The glowing accretion disk is formed by gases from the living star’s atmosphere flowing towards and surrounding the black hole (stock illustration)

The study, published today in Nature Astronomy, also sheds light on how black holes are created from the cores of dying stars.

The star that gave birth to VFTS 243 appears to have collapsed entirely, leaving no trace of a powerful supernova explosion.

Dr Shenar explained: “Evidence for this ‘direct collapse’ scenario has recently emerged – but our study provides arguably one of the most direct indications.”

“This has huge implications for the origin of black hole mergers in the cosmos.”

It took six years of data from ESO's Very Large Telescope (pictured) to identify VFTS 243

It took six years of data from ESO’s Very Large Telescope (pictured) to identify VFTS 243

The FLAMES instrument, mounted on the Nasmyth A platform of ESO's Very Large Telescope.  FLAMES is a high resolution spectrograph of the VLT and can access targets over a wide corrected field of view.  It allows to observe more than a hundred objects at the same time

The FLAMES instrument, mounted on the Nasmyth A platform of ESO’s Very Large Telescope. FLAMES is a high resolution spectrograph of the VLT and can access targets over a wide corrected field of view. It allows to observe more than a hundred objects at the same time

Artist's rendering of NASA's Chandra X-ray Observatory Space Telescope

Artist’s rendering of NASA’s Chandra X-ray Observatory Space Telescope

Despite the nickname “black hole police”, the international team of researchers actively encourages scrutiny of their work.

Lead author Dr Tomer Shenar from the University of Amsterdam said: ‘As a researcher who has debunked potential black holes in recent years, I was extremely skeptical of this finding.

“For the first time, our team has come together to report on the discovery of a black hole – instead of dismissing one.”

Dr. Kareem El-Badry of Harvard University in Boston is dubbed the “Black Hole Destroyer” due to his notoriety for his debunking discoveries.

Dr El-Badry said: ‘When Tomer asked me to double-check his findings, I had my doubts.

“But I couldn’t find a plausible explanation for the data that didn’t implicate a black hole.

“Of course, I expect others in the field to carefully consider our analysis and try to concoct alternative models.

“It’s a very exciting project to be involved in.”

WHAT’S IN A BLACK HOLE?

Black holes are strange objects in the universe that get their name from the fact that nothing can escape their gravity, not even light.

If you venture too close and cross the so-called event horizon, the point from which no light can escape, you will also be trapped or destroyed.

For small black holes, you would never survive such a close approach anyway.

Tidal forces near the event horizon are enough to stretch any matter until it is just a string of atoms, in a process physicists call “spaghettification.”

But for large black holes, like the supermassive objects at the heart of galaxies like the Milky Way, which weigh tens of millions or even billions of times the mass of a star, crossing the event horizon would be uneventful.

Because it should be possible to survive our world’s transition to the world of black holes, physicists and mathematicians have long wondered what that world would look like.

They turned to Einstein’s general relativity equations to predict the world inside a black hole.

These equations work well until an observer reaches the center or the singularity, where in theoretical calculations the curvature of spacetime becomes infinite.

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