Stand anywhere close to the equator or in the Southern Hemisphere, and, come nightfall between April and September, a beautiful bright blob will be visible in the night sky. It’s Omega Centauri, a globular cluster of 10 million densely packed stars thought to be the remains of an ancient galaxy consumed by the Milky Way. Globular clusters are considered billions of years old and primarily made up of ancient stars.
A new study now reveals it to contain a black hole, but not just any kind—a “missing link” bridging the gap between those created by stars and supermassive black holes found in centers of galaxies.
Black Holes
The Milky Way contains a supermassive black hole, Sagittarius A*, which is about 27,000 light-years from the solar system at the galaxy’s center. In March, scientists published a spectacular new polarised light image of the strong magnetic fields spiraling from its edge. It came from the same team of over 300 international scientists at the Event Horizon Telescope that produced the first-ever image of Sagittarius A* in 2022. First discovered in 1974, it’s about 22 million miles across and a powerful source of radio waves.
The one found in Omega Centauri—the largest and brightest of the 150 globular clusters in the Milky Way’s outskirts—is far smaller. Black holes created by the destruction of stars have a mass between one and a few dozen times that of our sun, while supermassive black holes have a mass of millions or billions of times more. Omega Centauri is around 8,200 suns times the sun’s mass, making it the only example of an intermediate-mass black hole ever found.
Hard To Find
Intermediate-mass black holes are hard to find because their central black holes get larger as galaxies grow—primarily through mergers with other galaxies. Long-suspected by astronomers, this new paper—published today in Nature by scientists from the Max Planck Institute for Astronomy in Heidelberg, Germany—suggests that Omega Centauri is the remaining core of a separate, minor galaxy that the Milky Way swallowed. Its central black hole, therefore, may have been frozen in time long ago.
To find it, the researchers used over 500 calibration images from the Hubble Space Telescope to create an enormous catalog of the motions of 1.4 million stars within Omega Centauri. Seven fast-moving stars were found in a small region at the cluster’s center—the tell-tale sign of a black hole.
Next, measurements of the same seven stars will be taken using the James Webb Space Telescope and the Extremely Large Telescope in Chile. Then, work will be done to discover how the stars accelerate by studying how their orbits curve.
Pick up my books Stargazing in 2024, A Stargazing Program For Beginners, and When Is The Next Eclipse?
Wishing you clear skies and wide eyes.
