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Milky Way Center Hosts Nearly 20,000 Black Holes

[Estimated read time: 3 minutes]
  • A new study indicates that there should be 10,000 to 20,000 black holes in just a 6 light-years-wide region, near center of the Milky way galaxy. 
  • Astrophysicist used Chandra X-ray Observatory data to verify their method. 
  • They were able to find 12 black holes within just 3 light years. 

Astrophysicists at Columbia University have discovered 12 new black holes positioned near Sagittarius A, Milky Way’s supermassive black hole. Previous studies suggest that the supermassive black holes present in the center of most galaxies are likely surrounded by several smaller black holes. However, this concept hasn’t been proven, until now.

So far, we’ve detected nearly 30 black holes in our 100,000 light-years-wide galaxy. This new research says that there should be 10,000 to 20,000 black holes in just a 6 light-years-wide region.

Since Sagittarius A is the closest supermassive black hole to Earth, it’s easiest to observe, and thus numerous finding have been made around it. Below, we’ve explained the findings of the latest research and how they came to this conclusion. Let’s start digging deeper into the space.

Black Holes Near Sagittarius A

The Sagittarius A is surrounded by a halo of dust and gas, which offers a perfect environment for the birth of giant stars. They live there for a long time period and eventually die, turning into black holes.

The supermassive black hole also influences the black holes present outside the halo, as it pulls them towards it when they lose their energy. These black holes are then held captive by the supermassive black hole’s force. While some of them are captured and bounded to a nearby star, creating a stellar binary, some of them remain isolated.

Credit: Interstellar / R. Hurt / Caltech

According to the researchers, these mated and isolated black holes are present in a large volume in the Galactic Center. They are creating a density cusp that gets even more crowded as distance to the supermassive black hole reduces.

In this study, astrophysicist discovered a total of 12 black holes within just 3 light years of Sagittarius A. They analyzed the spatial distribution and properties of the detected binary systems, and concluded that there should be approximately 10,000 isolated black holes and 500 low-mass binaries nearby Sagittarius A.

Reference: Nature | doi:10.1038/nature25029 | Columbia News 

How Did They Find These Black Holes?

In the last couple of decades, researchers have made numerous attempts to find such a cusp, but they were not getting any positive results, probably because they were looking for specific event called X-ray bright burst, which is produced by the matter of companion star as it falls into the black hole.

Since Galactic Center is over 24,000 light years away from our solar system, it’s very difficult to see those bursts. In fact, they are only strong enough to see once every 1,000 years (or less). Therefore, instead of going for bright bursts, researchers plan to look at the weaker, but consistent X-rays that are produced by inactive black hole binaries.

Unlike neutron star binaries, black hole binaries do not emit big bursts, making it hard to observe. Moreover, Isolated black holes don’t emit any light, so it’s not a good idea to find any of them either.

Chandra 2–8-keV image of the Galactic Centre with X-ray sources

However, when black hole eats a low mass star, it emits a fainter but steadier X-ray bursts that are detectable. So if we identify the total number of black holes coupled with low-mass stars, we could tell the population of isolated black holes.

Read: How Strong Are Black Holes? | Precise Measurement of Magnetic Field

The research team used Chandra X-ray Observatory data to verify their method. They looked for low mass binaries’ (which are in inactive state) X-ray signature and were able to detect a dozen of black holes. This information will help astrophysicist to accurately predict the number of gravitational wave events associated with black holes out there.

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