NASA's Hubble Space Telescope Confirms First Solitary Black Hole in Milky Way

In a breakthrough discovery that deepens our understanding of black holes and the cosmos, NASA’s Hubble Space Telescope has helped astronomers confirm the first-ever detection of a solitary stellar-mass black hole — a black hole that exists alone, without a companion star. Located approximately 5,000 light-years away in the direction of the constellation Sagittarius, this isolated cosmic entity had been under study since 2011.

A Decade-Long Mystery Solved

The trail leading to this discovery began in 2011 when astronomers first observed a mysterious object causing the light of a background star to momentarily brighten and shift — a phenomenon known as gravitational microlensing. In 2022, Kailash Sahu and his team at the Space Telescope Science Institute in Baltimore announced their belief that this object was a black hole. However, the interpretation was soon challenged by another research group, which proposed it was a neutron star.

Now, with the aid of more recent data collected by the Hubble Space Telescope (2021–2022) and ESA’s Gaia spacecraft, Sahu’s findings have been confirmed: the object is indeed a black hole. Notably, it marks the first confirmed case of a stellar-mass black hole existing alone in space — not drawing matter or light from any nearby object, and thus exceptionally hard to detect.

“It’s the only one so far,” said Kailash Sahu, emphasizing the rarity and significance of this detection.

How the Lone Black Hole Was Detected

Most black holes discovered to date are found in binary systems — paired with a visible star — which makes it easier for astronomers to detect their gravitational influence. In contrast, solitary black holes, while theoretically abundant, are incredibly difficult to identify due to their invisibility and lack of light emission.

The breakthrough was made possible by observing how the black hole bent and magnified the light from a background star as it passed in front of it. This rare gravitational lensing event provided clues about the object’s mass and nature.

The microlensing signal, combined with precision measurements of the star’s position over several years, enabled researchers to confirm that the lensing object is about seven times the mass of our Sun — too massive to be a neutron star.

What’s Next: Roman Space Telescope Mission

This newly confirmed solitary black hole, while already a milestone in astronomy, may be just the beginning. According to Sahu, the upcoming Nancy Grace Roman Space Telescope, expected to launch in 2027, will be pivotal in finding many more such black holes by expanding the reach and sensitivity of microlensing surveys.

As Sahu notes, “We believe there are hundreds of millions of such black holes in our galaxy alone.” The discovery of this solitary black hole provides a critical proof-of-concept for identifying them.