When stars die massive enough to eclipse our sun, they explode into a supernova and the remaining core is crushed by its own gravity, forming a black hole.
At times, the blast can send the black hole in motion, launching itself across the galaxy like a pinball. By right, there should be many traveling black holes known to scientists, but they are virtually invisible in space and therefore very difficult to discover.
Astronomers believe that 100 million free-floating black holes travel across our galaxy. Now, researchers believe they have detected this object. The detection was made after six years of observations, and astronomers were even able to make an accurate measurement of the mass of the extreme cosmic object.
The black hole is 5,000 light-years away, located in a spiral arm of the Milky Way called Carina-Sagittarius. This observation allowed the research team to estimate that the closest isolated black hole relative to Earth could be just 80 light-years away.
But if black holes are essentially indistinguishable from the vacuum of space, how did this Hubble detect it?
The extremely strong gravitational field of the black holes distorts the space around it, creating conditions that can deflect and amplify the light from the stars that line up behind them. This phenomenon is known as gravitational lenses. Terrestrial telescopes look at the millions of stars that dot the center of the Milky Way and look for this ephemeral brightness, which means that a large object has passed between us and the star.
Hubble is well prepared to follow these observations. Two different teams of researchers studied the observations to determine the mass of the object. Both studies have been accepted for publication in The Astrophysical Journal.
A team led by astronomer Kailash Sahu, a Hubble instrument scientist at the Baltimore Space Telescope Science Institute, determined that the black hole weighed seven times the mass of our sun. The second team, led by PhD student Casey Lam and Jessica Lu, an associate professor of astronomy, both at the University of California, Berkeley, reached a smaller mass range of 1.6 to 4. 4 times that of the sun. According to this estimate, the object could be a black hole or a neutron star. Neutron stars are the incredibly dense remnants of exploded stars.
“Whatever it is, the object is the first dark stellar remnant discovered to roam the galaxy, unaccompanied by another star,” Lam said in a statement.
The black hole passed in front of a background star located 19,000 light-years from Earth toward the center of the galaxy, amplifying its stellar light for 270 days. Astronomers had a hard time determining its measurement because there is another bright star very close to the one they observed glowing behind the black hole.
“It’s like trying to measure the small movement of a ladybug next to a bright light bulb,” Sahu said in a statement. “We had to subtract the light from the nearby bright star carefully to accurately measure the dimming of the dim source.”
Sahu’s team believes that the object can travel at a speed of 99,419 miles per hour (160,000 kilometers per hour), which is faster than most stars in this part of the galaxy, while the team of Lu and Lam reached an estimate of 67,108 miles per hour (108,000 kilometers per hour).
More Hubble data and observations and subsequent analysis could resolve the object identity argument. Astronomers continue to search for needles in a barn of more than one of these invisible rarities, which could help them better understand how stars evolve and die.
“With microlenses, we can probe these solitary, compact objects and weigh them. I think we’ve opened a new window on these dark objects, which can’t be seen any other way,” Lu said.