Astronomers spot a wandering black hole in empty space for the first time

And this is only the beginning.
Mert Erdemir
HST image of the source star encircled in green. Arxi

There have been many recent developments in the field of black holes, and with each discovery, it turns out how endless their potentials are. For instance, there is even one black hole that eats its host star to death. This time, an international team of researchers announced on January 31 that they have spotted an isolated stellar-mass black hole that is wandering around in interstellar space for the first time. Their findings, though not peer-reviewed yet, were published on the arXiv preprint server.

Although astronomers have already assumed for a while that there are abounding free-floating black holes in space, the discovery of one has taken until now. The reason behind the discovery taking so long is the difficulty of observing them in the black backdrop of space.

This discovery is a continuation of a finding in 2011 when two project teams -- the Optical Gravitational Lensing Experiment (OGLE) run by the University of Warsaw in Poland, and the Microlensing Observations in Astrophysics (MOA) survey conducted by researchers in New Zealand and Japan -- noted that they spotted an extremely bright star that is 20,000 light-years away from Earth. Since then, Kailash Sahu from the Space Telescope Science Institute in Baltimore, the lead author on the arXiv preprint, used the Hubble Space Telescope with his colleagues for six years to observe the object. During the process, they carried out precise astrometry by analyzing the data provided by the Hubble Space Telescope (HST).

What they found, in the end, was that the star changed its location. As the researchers kept studying the star and its light, they ended up eliminating the possibility of any light emanating from the lensing and ensuring that the magnification lasted for a long time. Both of these are necessary to make sure of the existence of a black hole.

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Black hole's deflection from August 2011 to 2017
Source: Arxiv

Consequently, the research proves the deflection of the free-floating black hole and contributes to our comprehension of black holes. The researchers even managed to calculate its speed. “It’s moving at about 45 kilometers per second,” Sahu says. Additionally, the team measured the size of the black hole, which is known to be 20,000 light-years from Earth, and found out that it is seven times bigger than our sun. 

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