Hubble Telescope detects stellar ‘ghost’ roaming the Milky Way

For the first time, the Hubble Space Telescope has detected a lone object adrift in our Milky Way galaxy — the unseen, ghostly remains of a once-radiant star.

When stars massive enough to shrink our Sun die, they explode in a supernova and the remaining core is crushed by its own gravity, forming a black hole.

Sometimes the explosion can set the black hole in motion, flinging itself across the galaxy like a pinball. By rights, there must be many roving black holes known to scientists, but they are virtually invisible in space and therefore very difficult to discover.

Astronomers believe that 100 million floating black holes roam our galaxy. Now, the researchers believe they have detected an object. The detection was made after dedicating six years observations — and scientists were able to make an accurate measurement of the extreme cosmic object’s mass.

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 to Earth could be just 80 light-years away.

But if black holes are essentially indistinguishable from the void of space, how did Hubble detect this one?

The extremely strong gravitational field of black holes distorts the space around them, creating conditions that can deflect and amplify light from stars that line up behind them. This phenomenon is known as gravitational lensing. Ground-based telescopes look at the millions of stars that dot the center of the Milky Way and look for that ephemeral glow, signifying that a large object has passed between us and the star.

Hubble is perfectly prepared to follow up on these observations. Two different teams of researchers studied the data to determine the object’s mass. Both studies have been accepted for publication in The Astrophysical Journal.

A team, led by astronomer Kailash Sahu, a Hubble instrument scientist at the Space Telescope Science Institute in Baltimore, determined that the black hole weighed seven times the mass of our Sun.

The second team, led by doctoral student Casey Lam and Jessica Lu, an associate professor of astronomy, both at the University of California, Berkeley, arrived at a lower mass range, between 1.6 and 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 wandering 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 towards the center of the galaxy, amplifying its starlight for 270 days. Astronomers have 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 tiny movement of a firefly next to a bright light bulb,” Sahu said in a statement. “We had to painstakingly subtract the light from the nearby bright star to accurately measure the deflection of the faint source.”

Sahu’s team thinks the object may be traveling as fast as 160,000 kilometers per hour, which is faster than most stars in that part of the galaxy, while Lu and Lam’s team came up with an estimate of 108,000. kilometers per hour.

More data and observations from Hubble and further analysis may resolve the dispute over the object’s identity. Astronomers continue the needle-in-a-haystack search for more of these unseen oddities, which could help them better understand how stars evolve and die.

“With the microlensing, we can probe these solitary, compact objects and weigh them. I think we’ve opened a new window for these dark objects, which can’t be seen any other way,” Lu said.