gpolit.com
gpolit.com April 24, 2018


Centre of Milky Way is teeming with black holes

06 April 2018, 01:44 | Camille Rivera

Are the Milky Way's borders expanding?

Milky Way is getting bigger, say scientists

A view of Sagittarius A*, the supermassive black hole at the center of the Milky Way, taken with the Chandra X-ray Observatory (circled in green).

The researchers found that star formation evolves by fits and starts.

The center of the Milky Way galaxy is filled with more than 10,000 black holes, according to a new study. In addition, "the galactic center is very crowded so it is hard to differentiate systems in which a black hole is present from other more prosaic X-ray sources such as white dwarfs".

"But black holes with a stellar companion make X-rays".

They used the ground-based SDSS telescope for optical data, and the two space telescopes GALEX and Spitzer for near-UV and near-IR data respectively, to look in detail at the colors and the motions of the stars at the end of the disk found in the other galaxies.

At the center of our galaxy lurks a supermassive black hole. The team suggests there could be hundreds of such black hole binaries at the centre of our galaxy and thousands of black holes without a companion star. Hailey and his colleagues went back through archived observations made by this telescope to look for evidence of black holes.

In the new study, Charles Hailey, an astrophysicist at Columbia University, and his colleagues scrutinized the past dozen years of data gathered by the Chandra X-ray Observatory, an orbiting craft whose instruments are created to detect high-energy radiation emitted by the immensely hot material surrounding exploded stars and near black holes.

Many galaxies, including our own, have one supermassive black hole at their core, which grows by slowly pulling in a host of smaller objects, including stars and entire star systems.

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

The researchers now believe there are around 300 to 500 black hole low-mass binaries surrounding Sagittarius A* on top of about 10,000 isolated black holes.

The work may also help shed light on how x-ray binaries form and develop, Harrison says.

In our neck of the galaxy, x-ray binary systems aren't so common. However, emissions from x-ray binaries that include neutron stars often surge suddenly and then subside at least once every 5 to 10 years, Hailey explains. In the journal Nature, the team now says they spotted a dozen black holes paired with stars all within just a few light-years of the central supermassive one.

We know that active star formation is going on in the region of our galactic centre.

Stars form as gas and dust succumb to gravity and fusion is ignited.

The Galaxy consists of several hundred billion stars, with huge amounts of gas and dust, all intermingled and interacting through the force of gravity.

GREENFIELDBOYCE: Now, black holes aren't the only things at the center of the galaxy. "It won't be quick, but if you could travel forward in time and look at the galaxy in 3 billion years' time it would be about five percent bigger than today", said Martínez-Lombilla.

"Isolated, unmated black holes are just black-they don't do anything".

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.

GREENFIELDBOYCE: Scientists have known for a long time that a giant black hole with 4 million times the mass of our sun appears to lie at the center of our galaxy, and the thinking has been that it should be surrounded by many, many other black holes that originally formed farther away.

"This finding confirms a major theory and the implications are many", said Hailey. And he hopes that other astronomers will use publicly available data to further seek out these somewhat elusive mysteries of the universe.



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