Astronomers recently made a groundbreaking discovery: a dormant black hole named Gaia BH3, residing about 1,926 light-years away in the Milky Way’s Aquila constellation. Known as a “sleeping giant,” Gaia BH3 is approximately 33 times the Sun’s mass, making it the largest stellar black hole known in our galaxy. This black hole is only the second nearest to Earth, with Gaia BH1 slightly closer at around 1,500 light-years away.

The find was unintentional. Researchers were sifting through data from the European Space Agency’s Gaia space telescope, anticipating an upcoming data release when they noticed an unusual wobbling motion in a nearby star. This disturbance revealed the presence of Gaia BH3, whose immense gravitational force was causing a nearby giant star to orbit around it. This wobble marked the third dormant black hole identified by Gaia, a significant milestone in astronomical research.

Unlike active black holes that feed on surrounding material and emit detectable X-rays, dormant black holes like Gaia BH3 lack a close companion to consume. Their presence is usually detected only when they exert gravitational effects on neighboring stars. Gaia BH3’s detection was made possible by Gaia’s data, which highlighted its unique influence on the companion star’s movement, sparking a deeper investigation.

To confirm the mass and characteristics of Gaia BH3, scientists utilized the European Southern Observatory’s Very Large Telescope (VLT) in Chile, along with other observatories. This research revealed that Gaia BH3 stands out as one of the most massive stellar black holes known. Typically, stellar black holes in the Milky Way are about ten times the Sun’s mass, with Cygnus X-1 previously holding the record at 21 times the Sun’s mass. Gaia BH3’s sheer size opens doors for new studies on stellar black holes and their unique characteristics.

A significant aspect of Gaia BH3’s formation is its metal-poor nature. Stellar black holes are thought to form from massive stars’ deaths. Gaia BH3’s mass suggests that it originated from the collapse of a metal-poor star. These ancient stars, composed mainly of hydrogen and helium, lose less mass during their lifetimes, retaining more material for high-mass black holes. While astronomers suspected this relationship between metal-poor stars and massive black holes, direct evidence was limited until Gaia BH3’s discovery. The chemical makeup of its companion star supports this theory, indicating both stars likely share an ancient, metal-poor origin.

The companion star’s trajectory also suggests a fascinating history. Its orbit within the Milky Way moves counter to the general motion of stars in the galactic disk, indicating it may have once belonged to a smaller galaxy that merged with the Milky Way over 8 billion years ago. This discovery not only hints at Gaia BH3’s ancient origins but also provides clues about the Milky Way’s own formation.

With future Gaia data releases, astronomers hope to uncover more about Gaia BH3 and similar massive stellar black holes. Gaia’s mission, originally intended to map stars, is evolving beyond its initial goals, significantly advancing our understanding of black holes and the broader structure of our galaxy. The next Gaia data release is anticipated in 2025, likely bringing new revelations in our cosmic neighborhood.