Key Takeaways:

  1. Astronomers have discovered Gaia BH3, the most massive known stellar black hole in the Milky Way, with a mass nearly 33 times that of the sun.
  2. This finding was unexpected, as the black hole was detected due to its gravitational influence on a nearby companion, highlighting the significance of Gaia’s observations.
  3. Gaia BH3’s formation from a metal-poor star offers direct evidence linking high-mass black holes with such stellar compositions, reshaping our understanding of black hole origins.
  4. The orbit of Gaia BH3’s companion suggests its origin in a small galaxy that merged with the Milky Way over 8 billion years ago, providing insights into galactic evolution.
  5. Gaia’s discoveries extend beyond its primary mission, revolutionizing astronomy by enabling the study of distant celestial objects like Gaia BH3 and enhancing our understanding of the universe’s vast complexities.

Astronomers have recently identified the most massive stellar black hole within the Milky Way galaxy. This discovery came about as they noticed an unusual wobble in the surrounding space.

Known as Gaia BH3, this colossal entity possesses a mass nearly 33 times that of our sun. Situated approximately 1,926 light-years away in the Aquila constellation, it stands as the second-closest black hole to Earth, following Gaia BH1, which is around 1,500 light-years distant and boasts a mass nearly ten times that of our sun.

The detection of Gaia BH3 occurred during the examination of data collected by the European Space Agency’s Gaia space telescope. Initially, researchers did not anticipate such a finding, but a peculiar motion, caused by Gaia BH3’s gravitational pull on a nearby companion, caught their attention.

Many dormant black holes lack nearby companions, making them challenging to detect as they do not emit any light. However, some stellar black holes attract material from companion stars, emitting bright X-rays observable through telescopes.

The observation of an aging giant star in the Aquila constellation revealed its orbital interaction with a dormant black hole, marking the third such discovery by Gaia.

To confirm Gaia BH3’s mass, astronomers utilized the European Southern Observatory’s Very Large Telescope and other ground-based observatories in Chile’s Atacama Desert. Additionally, their study provided insights into the formation of such massive black holes. These findings were published in the journal Astronomy & Astrophysics.

Lead study author Pasquale Panuzzo, an astronomer at the Observatoire de Paris, expressed surprise at the discovery, stating, “No one was expecting to find a high-mass black hole lurking nearby, undetected so far. This is the kind of discovery you make once in your research life.”

Regarding supermassive black holes like Sagittarius A* at the Milky Way’s center, which surpass Gaia BH3’s mass by millions of times, their formation remains poorly understood. However, while supermassive black holes form from massive cosmic cloud collapses, stellar black holes arise from the deaths of massive stars. Thus, Gaia BH3 represents the most massive stellar black hole in the galaxy formed from the death of a massive star.

Before Gaia BH3’s discovery, Cygnus X-1 held the title of the largest known stellar black hole in the Milky Way, with a mass 21 times that of the sun. Gaia BH3’s mass places it among objects found in distant galaxies, highlighting its significance.

Three stellar black holes found in our galaxy, Gaia BH1, Cygnus X-1 and Gaia BH3, have masses that are 10, 21 and 33 times that of the sun, respectively. - M. Kornmesser/ESO
Three stellar black holes found in our galaxy, Gaia BH1, Cygnus X-1 and Gaia BH3, have masses that are 10, 21 and 33 times that of the sun, respectively. – M. Kornmesser/ESO

Scientists propose that stellar black holes like Gaia BH3 form from the collapse of metal-poor stars, which contain primarily hydrogen and helium. These stars lose less mass throughout their lifespan, resulting in a surplus of material during collapse, potentially leading to the formation of high-mass black holes.

Notably, Gaia BH3’s discovery provides direct evidence linking high-mass black holes with metal-poor stars, as confirmed by the metal-poor composition of its orbiting companion.

The orbit of the star accompanying Gaia BH3 suggests it formed within the first 2 billion years after the universe’s creation, moving counter to many stars in the Milky Way’s galactic disk. This trajectory indicates its origin as part of a small galaxy that merged with the Milky Way over 8 billion years ago.

The research team anticipates that their findings will enable other astronomers to study Gaia BH3 further, unlocking more of its mysteries before the full Gaia data release scheduled for late 2025.

Carole Mundell, the European Space Agency’s director of science, praised Gaia’s impact on astronomy, stating, “It’s impressive to see the transformational impact Gaia is having on astronomy and astrophysics. Its discoveries are reaching far beyond the original purpose of the mission, which is to create an extraordinarily precise multi-dimensional map of more than a billion stars throughout our Milky Way.”

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