This is an illustration of a close-up look at a black hole drifting across our Milky Way galaxy. … [+] The black hole distorts the space around it, distorting the images of background stars lined up almost directly behind it.
FECYT, IAC
For the first time, astronomers using NASA’s Hubble Telescope have reported observing a free-floating black hole completely independent of a companion mass star.
So far, black holes have only been identified as supermassive objects in the center of massive galaxies like our own Milky Way, or gravitationally bound to a stellar companion. Although these free-floating black holes have long been predicted to exist, this is the first time such an object has been detected.
Two separate observation crews, one led by the Maryland Space Telescope Science Institute and one led by the University of California at Berkeley, announced the findings today and detailed their observations in accepted articles in The Astrophysical Journal. The Astrophysical Journal Letters.
After six years of careful observation, NASA’s Hubble Space Telescope has detected a wandering black hole about 5,000 light-years away in the Carina-Sagittarius spiral arm of our galaxy, NASA reported.
The equipment used Hubble to capture the object by distorting space-time using gravitational microlenses. With the microlens, a foreground object can act as a gravitational lens to bend and amplify the light of a distant background star. In this case, a black hole showed a star about 19,000 light-years away in the galactic protuberance of our Milky Way galaxy. One of the reasons the teams suspected that this foreground lens object was actually a black hole was due to the length of the lens event which was amplified for 270 days.
Because two separate surveys captured the same object, this putative black hole has two names, known in part from the lens events in which they were found: MOA-2011-BLG-191 and OGLE-2011-BLG-0462.
This illustration reveals how the light of a background star is deflected and illuminated by black … [+] intense gravitational field of the hole. The Hubble Space Telescope is looking for these black holes looking for distortion in the light of stars as the black hole drifts in front of the background stars.
NASA, ESA, STScI, Joseph Olmsted
How do these black holes end up as solo objects?
The most likely scenario is for giant stars, at least 20 times the mass of the Sun, to explode as supernovae. The resulting remaining stellar core is crushed by gravity in a black hole, says NASA. Because self-detection is not perfectly symmetrical, the black hole can be kicked and pass through our galaxy like a cannonball, NASA points out.
What is the actual size of this black hole?
Theoretical models suggest that the mass of the parent of this black hole is 20 to 25 solar masses, which means that the parent must be an O-type star, Kailash Sahu, an astronomer at the Institute of Telescope Science Space and lead author of The Astrophysical Journal, he told me.
O-type stars, which still burn hydrogen in what is known as the main sequence, oscillate up to 90 times the mass of our Sun and can be a million times brighter than our own star.
Sahu says that if this black hole of solar mass is 7.1 times the mass of our Sun, its event horizon (or its outer limit) would be about 26 miles in diameter.
How fast is it traveling across the galaxy?
The Sahu team, NASA says, estimates that the isolated black hole travels across the galaxy at 100,000 miles per hour (fast enough to travel from Earth to the Moon in less than three hours).
Although the microlens is a spot detection, Sahu says it might still be possible to make tracking observations of this freely floating black hole.
“We estimate that the black hole is in a high-density region of interstellar matter,” Sahu said. In that case, the black hole would accumulate interstellar matter that would produce X-rays and radio waves, he says.
Therefore, deep X-ray and radio observations can detect the black hole, which can be used to better characterize the object, Sahu says.
How many of these free floats could be inside our galaxy?
Estimates range from 100 to 200 million, and the nearest is expected to be at least 80 light-years from Earth.