A tight knot of stars nearly as old as the universe hides a dark secret at its core.
The spherical cluster NGC 6397, a conglomeration of stars about 7,800 light-years from Earth, likely harbors a group of tiny black holes in the heart, a new study reports.
Researchers studied the movement of stars in NGC 6397 with the help of NASAs Hubble Space Telescope and that of the European Space Agency Gaia spacecraftThese movements revealed the existence of a hidden mass in the center of the cluster – a “central dark component” that makes up 0.8 to 2% of NGC 6397’s total mass.
Pictures: Black holes of the universe
That derived mass corresponds to an intermediate black hole, a cosmic beast halfway between massive black holes that form after the collapse of large stars, and the supermassive beasts that reside in the cores of most, if not all, galaxies.
Intermediate black holes are elusiveOnly a few candidates have been discovered to date. And NGC 6397’s dark masses are not among those privileged ranks.
“The small effective radius of the diffuse dark component suggests that it is composed of compact stars (white dwarfs and neutron stars) and black holes of stellar mass,” wrote Eduardo Vitral and Gary Mamon, both of the Paris Institute of Astrophysics in France, subscribed the new study, which was published online Thursday (Feb. 11) in the journal Astronomy & Astrophysics.
The black holes of stellar mass “should dominate the mass of this diffuse dark component unless more than 25% escapes from the cluster,” they added.
“Ours is the first study to provide both the mass and magnitude of what appears to be a collection of mostly black holes in the center of a globular cluster collapsed into the core,” Vitral said in a statement NASA statement, referring to a type of cluster with a particularly dense core.
The new study could have applications resounding far beyond NGC 6397, one of the closest globular star clusters on Earth. For example, if densely packed black holes are a common feature of collapsed clusters such as Vitral and Mamon, these collections of stars could be a prominent source of the gravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory
Mike Wall is the author of “Outside(Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the quest for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.