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First discovered: a lonely and wandering black hole

First discovered: a lonely and wandering black hole

sSince May 2022, there has been no doubt that a supermassive black hole exists in the center of our galaxy, the Milky Way. After years of work, an international team of researchers has been able to capture a “photo” of this gravitational monster called Sagittarius A* with the help of eight radio telescopes.

In the Astrophysical Journal, researchers presented evidence of a second black hole in the Milky Way. Unlike Sagittarius A*, it is not a stationary black hole, but an object that is cruising through the galaxy at high speed.

Scientists have never before directly detected a single black hole roaming through interstellar space – although theoretical considerations suggest there are more than 100 million roaming black holes in our galaxy.

Maybe 80 light years away from us

The black hole that has now been discovered is about 5,000 light-years away from Earth and is located in Kareena Sagittarius The spiral arm of our galaxy. From this information and complex statistical calculations, the researchers concluded that the closest black hole to Earth may be only 80 light-years away from us. For comparison: the nearest star – after the Sun – is located a little more than four light-years away.

The first discovery of a roaming black hole was made with measurements from Hubble Space Telescope. This method allowed to determine not only the distance of an object, but also its speed and mass.

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Accordingly, the black hole rushes through the Milky Way at a speed of 160 thousand kilometers per hour. Researchers determined its mass is seven times that of the Sun. Thus, this vagrant black hole is noticeably less massive than Sagittarius A* at the center of the galaxy. This gravitational monster has four million solar masses.

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Seven times the mass of the sun

The relatively small mass of the newly discovered black hole fits well with the theoretical expectations of astrophysicists, who postulated the existence of such celestial bodies for a very long time. It is said to be only 20 times larger than our sun and was formed during supernova explosions of larger stars.

The core remaining in a black hole is supposed to explode due to gravitational forces. Because this implosion is not perfectly symmetric, the black hole that forms receives a thrust so that it thrusts through space, like a shot from a cannonball.

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This artist's rendering shows one of the most primitive supermassive black holes known (the central black point) in the heart of a young, star-rich galaxy.  (Photo: Photo12/Universal Images Group via Getty Images)

But how does the Hubble telescope, operating in the optical wavelength range, locate a lone black hole when it emits no visible light at all, and is not surrounded by material that emits detectable radiation? In the case of Sagittarius A*, the “image” was only possible because this black hole is surrounded by matter.

Fine lens detection enabled

This so-called accretion disk is gradually being swallowed by the black hole and heated up considerably in the process. The “image” of Sagittarius A* is, after all, a picture of the radiation emitted from the immediate vicinity of the black hole.

Although a single black hole does not contain this radiation, researchers have still been able to detect it. This is because it bends the surrounding space due to its gravity. This curvature leads, among other things, to the fact that light from distant stars is on its way to Hubble telescope Flies close to the invisible black hole deviate slightly from its orbit.

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Researchers talk about the so-called effect of microlensing. They demonstrate the accuracy of the observed deflection of light with the following example: what Hubble was able to establish corresponds to the observation of a coin located in Los Angeles using a telescope in New York, proving that the position of the coin was shifted by two centimeters.

Hubble was measured for six years

The challenge of such an accurate measurement can be seen from the fact that Hubble has collected data over a period of six years to prove the existence of this black hole.

Measurement data were evaluated by two independent research groups – on the one hand by a team at Space Telescope Science Institute in Baltimore under the supervision of Kailash Sahu and on the other hand by scholars from University of California at BerkeleyDirected by Casey Lamm.

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Professor Reinhard Genzel with the VLT telescope (image montage)

The two teams came to slightly different conclusions, particularly regarding the mass of the vagrant’s body. In the case of the Lamm team, this is a bit smaller, which leaves a small possibility that it could not be a black hole but a neutron star.

The explanation is not entirely certain yet

“As much as we tend to say it’s definitely a black hole, we can’t hide the fact that there could be other possible explanations,” says Berkeley researcher Jessica Lu.

The search for unseen wanderers in the Milky Way will continue. With masses slightly larger than when such an object was first discovered, it could then prove its nature as a black hole with a greater degree of certainty.

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However, it is clear what further research will look like. Sahu notes that “there is no other way to detect isolated black holes than by measuring the effect of a microlensing”.