Hubble spy ‘ghost’ roaming the Milky Way

For the first time, the Hubble Space Telescope has detected a lone object floating in our Milky Way galaxy – the invisible, spectral remnant of a once glowing star.

When stars large enough to make our sun look like a dwarf star die, they explode and form a supernova. The remaining core is crushed by its own gravity, forming a black hole.

Sometimes an explosive black hole can be set in motion, moving through the galaxy like a pinball. Theoretically, there should be many orbiting black holes known to scientists, but since they are not actually visible in space, they are very difficult to detect.

Astronomers believe that 100 million black holes are orbiting freely in our galaxy. Now, researchers believe they have discovered one of these objects. Astronomers were able to accurately measure the mass of this vast cosmic object, and it was discovered six years after its dedication to observation.

The black hole is 5,000 light-years away in the spiral arm of the Milky Way galaxy known as the Sagittarius Arm. This observation allowed the research team to estimate that the isolated black hole closest to Earth may be just 80 light-years away.

But if black holes are basically indistinguishable from space, how could Hubble detect it?

The strongest gravitational field of black holes distorts the space around them, creating conditions for the deformation or diffusion of stellar radiation behind them. This phenomenon is called gravitational lensing. Earth-based telescopes look at millions of stars in the center of the Milky Way and search for this impermanent glow that indicates that a large object has passed between us and the star.

Hubble was perfectly placed to follow these observations. Two different teams of researchers studied the observations to determine the mass of the object. Both studies have been approved 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, has determined that this black hole is seven times the mass of our Sun.

The second team, led by Casey Lam and Jessica Lou, PhD students who are associate professors of astronomy at the University of California-Berkeley, found that the mass of an object is between 1.6 and 4.4 times smaller than that of the Sun. According to this estimate, the object could be a black hole or a neutron star. Neutron stars are very dense remnants of exploding stars.

“Anyway, that object was the first dark star found to orbit the galaxy, not another star companion,” Lam said in a statement.

The starry sky seen in this Hubble image is in the center of the galaxy.

The black hole is a background star 19,000 light-years from Earth that extends its stellar light 270 days from the front to the center of the galaxy. Astronomers have struggled to determine their dimensions because there is another bright star very close to what they observe emitting light from behind a black hole.

“It’s like trying to measure the small movement of a firefly next to a flashing lightbulb,” Sahu said in a statement. “We had to very carefully remove the light from a nearby glowing star to accurately measure the deflection of the dim light source.”

The Sahu team expects the object to travel at 160,000 kilometers per hour, faster than most of the stars in that part of the galaxy, while the Lu and Lam team estimated speeds at 108 000 kilometers per hour.

Further data and observations by Hubble and further analysis can resolve doubts about the identity of the object. Astronomers are still searching for these singular objects that do not look like needles in a haystack, which will help them better understand how stars grow and die.

“With the microlensing process, we are able to research these compact, solitary objects and weigh them. I think we’ve opened a new window for these black objects, it’s not looking the other way. “


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