Astronomers Detect Lonely Black Hole in Globular Cluster NGC 3201

Thursday, 18 Jan, 2018

This indicates that the globular cluster contains an extensive black hole system within its core, with the radius expansion caused by the interaction between black holes and stars. Led by astronomers from the University of Göttingen in Germany, an global team of researchers made the discovery using the ESO's Multi Unit Spectroscopic Explorer, an instrument that helps the Very Large Telescope pick up objects that can't be studied with traditional imaging surveys.

Indeed, the star was "hooked", not by some fantastical cosmic fisherman, but by a black hole's gravity - and it turns out that this black hole is a little bit special.

Astronomers report through a study published January 9, that this recent discovery suggests there are actually more stellar-mass binary black holes in the Universe than previously thought and confirms that such objects can exist within star clusters.

"Until recently, it was assumed that nearly all black holes would disappear from globular clusters after a short time and that systems like this should not even exist!" said Benjamin Giesers, of Georg-August-Universität Göttingen, Germany, in an ESO statement.

If confirmed, this would be the first black hole that astronomers have ever been found in a globular cluster - a densely packed group of ancient stars - by looking at the black hole's gravitational pull on another object.

Based on observations of the star's properties, the researchers determined it to be about 0.8 times the mass of the Sun.

This image from the NASA/ESA Hubble Space Telescope shows the central region of the rich globular star cluster NGC 3201 in the southern constellation of Vela (The Sails). But just as nebulae can teach us about how young stars form, globular clusters can teach us about how old stars evolve and age - which occasionally ends with an older, massive star collapsing into a black hole. With this new finding, the team have for the first time been able to detect an inactive black hole at the heart of a globular cluster - one that is not now swallowing matter and is not surrounded by a glowing disk of gas. Since star clusters don't produce new stars continuously, such stellar-mass black holes in them would become the most massive objects. "Our discovery is the first direct detection of the gravitational effects of a stellar-mass black hole in a globular cluster".

Bottom line: Astronomers observed the unusual behavior of a star in the globular cluster cluster NGC 3201 and concluded it must be orbiting a four-solar-mass black hole. A dormant black hole, while still exerting a phenomenal gravitational force on its surroundings, would be entirely invisible to anyone who passed by.

The system was initially thought to be a binary star system, and a triple star system consisting of a double neutron star with a main star orbiting around it.

Unlike active black holes, the black hole in this system - if it truly exists - isn't swallowing matter or expelling gas.

Artist's impression of the black hole-star system in NGC 3201, a globular cluster located approximately 16,300 light-years away towards the southern constellation Vela. Among the plethora of radial velocity measurements taken for the globular cluster survey, the researchers found one oddball star.

A distant star in the cluster NGC 3201 that's exhibiting odd behavior may be drawing attention to a secret.