Astronomers may have spotted a wandering black hole for the first time
Astronomers may have detected the first-ever wandering black hole thanks to the ingenuity of researchers and the precision measurements made possible by the Hubble Space Telescope, CNET reported.
NASA estimates that there are more than 100 million black holes in our galaxy, the Milky Way, even though nobody has so far identified one conclusively. It is difficult to gather evidence of an object that does not reflect light. The blackhole photos that have been popular on the internet are actually images of the Event Horizon and not a Black Hole per se.
Astronomers, therefore, turned to another ability of black holes to warp space to detect them. When a black hole passes between Earth and a distant star, the warping of space results first in deflection and then amplification of starlight. The telescopes gaping at the sky for such events can capture this phenomenon called gravitational microlensing, which is then followed up by the Hubble Space Telescope.
How does the Hubble Space Telescope help?
Depending on the gravity of the black hole, a lensing event can extend over 200 days, NASA's Hubblesite states. The Space Telescope's precise measuring instruments are then tasked to measure the deflection of the background star's light. The deviation is usually in millarcseconds, which the website suggests is similar to "measuring the diameter of a 25-cent coin in Los Angeles as seen from New York City." This deviation is then used to determine the mass, distance, and velocity of the black hole.
Jessica Lu, an associate professor of astronomy at the University of Berkely, has been looking at free-floating black holes since 2008. She came across the photometric data from two microlensing surveys, one from a 1.3 m telescope in Chile called Optical Gravitational Lensing Experiment (OGLE) and another from Microlensing Observations in Astrophysics (MOA), from a 1.8 m telescope in New Zeland.
Since both these observations were of the same object, it has been shortened to OB110462 instead of using separated nomenclature given to it in each of the observing telescopes. After the Hubble Space Telescope observed the event, the researchers also had astrometric or positional data of the event, which they probed into further.
What did the researchers find?
Data for OB110462 showed that the lensing had occurred for a period of nearly 300 days by a dark compact object. Interestingly, the astrometric data also showed that a change in the star's position due to the gravitational influence of the lens was observed even a decade after the event, a UC Berkely press release said. Lu and her team have estimated that the lensing object is 1.6 - 4.4 times the mass of the Sun.
Since astronomers believe that a dead star must have a mass of at least 2.2 times that of the Sun to become a black hole, the researchers are open to the possibility that what they have observed is a neutron star.
Another team of researchers led by Kailash Sahu at the Space Telescope Science Institute in Maryland also studied Hubble's data for the event to conclude that the black hole is traveling at 100,000 miles an hour (160,000 kph), faster than its neighboring stars, Hubblesite reported. Sahu's team, however, has estimated the mass of the object to be seven times that of the Sun, making it, indisputably, a black hole.
So far, star-sized black holes have always been found as binary systems, so the observation of a single unpaired star is also a first for astronomers. More light will be shed on this when more observations from Hubble Space Telescope arrive this fall.
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