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Title: ESA's Gaia mission discovers the biggest stellar black hole in our
galaxy yet

Date: Wed, 17 Apr 2024 08:57:53 +0000
Link: https://www.engadget.com/esas-gaia-mission-di...

In addition to the supermassive black hole at the center of our galaxy, the
Milky Way also serves as home to smaller stellar black holes that form when a
massive star collapses. Scientists believe there are 100 million stellar
black holes in our galaxy alone, but most of them have yet to be discovered.
The ones that had already been found are, on average, around 10 times the
size of our sun, with the biggest one reaching 21 solar masses. Thanks to the
information collected by the European Space Agency's Gaia mission, though,
scientists have discovered a stellar black hole that's 33 times the size of
our sun, making it the biggest one of its kind we've ever seen in our galaxy
so far. It's also relatively close to our planet at around 1,926 light-years
away.

Gaia BH3, as it's now called, was first noticed by a team of ESA scientists
poring over data from the mission to look for anything unusual. An old giant
star from the nearby Aquila constellation caught their attention with its
wobbling, leading to the discovery that it was orbiting a massive black hole.
BH3 was hard to find despite being so close ΓÇö it's now the second closest
known black hole to our planet ΓÇö because it doesn't have celestial bodies
close enough that could feed it matter and make it light up in X-ray
telescopes. Before its discovery, we'd only found black holes of comparable
size in distant galaxies.

The ESA team used data from ground-based telescopes like the European
Southern Observatory to confirm the size of the newly discovered celestial
body. They also published a paper with preliminary findings before they
release a more detailed one in 2025, so that their peers could start studying
Gaia BH3. For now, what they know is that the star orbiting it has very few
elements heavier than hydrogen and helium, and since stellar pairs tend to
have similar compositions, the star that collapsed to form BH3 could've been
the same.

Scientists have long believed that it's the metal-poor stars that can create
high-mass black holes after they collapse, because they lose less mass in
their lifetimes. In other words, they'd theoretically still have a lot of
materials left by the time of their death to form a massive black hole. This
was apparently the first evidence we've found that links metal-poor stars
with massive stellar black holes, and it's also proof that older giant stars
developed differently than the newer ones we see in our galaxy.

We'll most likely see more detailed studies about binary systems and stellar
black holes that use data from BH3 and its companion star in the future. The
ESA believes that BH3's discovery is just the beginning, and it's going to be
the focus of more investigations as we seek to unravel the mysteries of the
universe.

This article originally appeared on Engadget at https://www.engadget.com/esas-
gaia-mission-discovers-the-biggest-stellar-black-hole-in-our-galaxy-yet-
085753239.html?src=rss

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