The discovery of 12 black holes around Sagittarius A *, the supermassive black hole at the center of the Milky Way

The discovery of 12 black holes around Sagittarius A *, the supermassive black hole at the center of the Milky Way

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A team of scientists suspects that the center of our galaxy, the Milky Way, may be full of black holes.

A new study published on Wednesday presents evidence that reinforces an old theory: “supermassive” black holes in the centers of galaxies are surrounded by many smaller ones.

The supermassive black hole at the center of the Milky Way is known as Sagittarius A * (Sgr A *).

Charles Hailey, of the University of Columbia, United States, led the study that concluded with the detection of a dozen inactive, low-mass “binary systems” near Sgr A *.

That is, they observed couples formed by a star and an invisible companion: the black hole.

The research was published in the journal Nature .

Haley’s team used file data from NASA’s Chandra X-ray telescope to get their conclusions.

Sgr A * is surrounded by a halo of gas and dust that creates the perfect breeding ground for the birth of massive stars(those that have at least 10 times the mass of the Sun).

When dying, these stars can become black holes.

Center of the Milky Way
Copyright of the AFP image
Image caption Previous searches at the center of the Milky Way had found little evidence of smaller black holes around Sgr A *.

In addition, it is believed that the black holes on the outside of the halo fall under the influence of Sgr A * as they lose their energy, which keeps them captive near it.

Some of these black holes join or become “companions” of passing stars, and form the binary systems that Hailey detected.

Weak is and constant

Previous searches at the center of the Milky Way had found little evidence of smaller black holes around Sgr A *.

Scientists were looking for bright bursts of X-rays that sometimes emit binary black holes.

But “the galactic center is so far from Earth that those explosions are strong and bright enough to see them once every 100 or 1,000 years,” said Professor Hailey.

This is why the astrophysicist and his colleagues, also from Columbia, the Harvard-Smithsonian Center for Astrophysics and the Pontificia Universidad Católica de Chile, took another path.

The team decided to look for the weakest but most stable X-rays that these binaries emit when they are inactive.

“The isolated and unbonded black holes are just black, they do nothing ,” Hailey said.

“But when black holes join with a low mass star, the marriage emits bursts of X-rays that are weaker, but constant and detectable,” he added.

Black hole
Copyright of the GETTY IMAGES image
Image caption Some massive stars turn into black holes when they die.

A search for X-ray emissions from binary black holes of low mass in the Chandra data showed 12 within a distance of three light-years from Sgr A *.

“But these are just the tip of the iceberg,” Hailey said according to the AFP news agency.

By extrapolating from the properties and distribution of these binary systems, the team estimated that there may be between 300 to 500 low-mass binary holes and about 10,000 isolated low-mass black holes around Sgr A *.

Gravitational waves

Professor Hailey said the finding “confirms an important theory” and added that “gravitational wave research will advance significantly because knowing the number of black holes in the center of a galaxy can help better predict how many wave events can be associated with them”.

Gravitational waves are distortions smaller than a proton in the space-time mesh.

They were predicted by Albert Einstein’s general theory of relativity and detected for the first time by the LIGO observatory in 2015.

One of the ways in which these waves arise is through the collision of black holes.

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