Small black holes found in the center of nearby stellar system
Today’s Video of the Day from NASA Goddard reveals that the globular cluster NGC 6397 is centered around a concentration of small black holes. This came as a surprise to astronomers, who had expected to find one massive black hole.
Globular clusters are stellar systems which have stars that are closely packed together. NGC 6397 contains more than 400,000 stars. The stellar system is relatively close to Earth, located at about 7,800 light-years away in the constellation Ara. According to NASA, NGC 6397 is almost as old as the Universe itself.
“We found very strong evidence for an invisible mass in the dense core of the globular cluster, but we were surprised to find that this extra mass is not ‘point-like’ (that would be expected for a solitary massive black hole) but extended to a few percent of the size of the cluster,” explained Eduardo Vitral of the Paris Institute of Astrophysics (IAP).
In collaboration with Gary Mamon, Vitral set out to detect the hidden mass by determining the velocities of the stars surrounding it.
“Our analysis indicated that the orbits of the stars are close to random throughout the globular cluster, rather than systematically circular or very elongated,” said Mamon.
The researchers concluded that the invisible mass must be made of the remnants of massive stars. “We used the theory of stellar evolution to conclude that most of the extra mass we found was in the form of black holes,” said Mamon.
“Ours is the first study to provide both the mass and the extent of what appears to be a collection of mostly black holes in the center of a core-collapsed globular cluster,” said Vitral.
Video Credit: NASA Goddard
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