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Title: Astronomers Confirm First 'Lone' Black Hole Discovery - and It's in
the Milky Way

Link: https://science.slashdot.org/story/25/04/20/2...

For the first time, astronomers have confirmed the existence of a lone black
hole," reports Science News - "one with no star orbiting it." It's "the only
one so far," says Kailash Sahu, an astronomer at the Space Telescope Science
Institute in Baltimore. In 2022, Sahu and his colleagues discovered the dark
object coursing through the constellation Sagittarius. A second team disputed
the claim, saying the body might instead be a neutron star. New observations
from the Hubble Space Telescope now confirm that the object's mass is so
large that it must be a black hole, Sahu's team reports in the April 20
Astrophysical Journal.... [And that second team has revised its assessment
and now agrees: the object is a black hole.] While solitary black holes
should be common, they are hard to find. The one in Sagittarius revealed
itself when it passed in front of a dim background star, magnifying the
star's light and slowly shifting its position due to the black hole's
gravity. This passage occurred in July 2011, but the star's position is still
changing. "It takes a long time to do the observations," Sahu says.
"Everything is improved if you have a longer baseline and more observations."
The original discovery relied on precise Hubble measurements of star
positions from 2011 to 2017. The new work incorporates Hubble observations
from 2021 and 2022 as well as data from the Gaia spacecraft. The upshot: The
black hole is about seven times as massive as the sun, give or take 0.8 solar
masses.... Located 5,000 light-years from Earth, this black hole is much
closer than the supermassive one at the Milky Way's center, which also lies
in Sagittarius but about 27,000 light-years from us. The star-rich region
around the galactic center provides an ideal hunting ground for solitary
black holes passing in front of stars. Sahu hopes to find additional lone
black holes by using the Nancy Grace Roman Space Telescope, slated for launch
in 2027.

Read more of this story at Slashdot.

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