The latest data from the Hubble Space Telescope suggests that a medium-sized black hole may be lurking within the Messier 4 star cluster.
Located approximately 6,000 light-years away from Earth at the core of the Messier 4 star cluster, this black hole has a mass equivalent to 800 suns, causing nearby stars to orbit it like an ” swarm of bees around a hive.”
Astronomer Eduardo Vitral from the Space Telescope Science Institute in Maryland, USA, stated: “It’s too small for us to consider it anything other than an individual black hole. Instead, it might be a stellar structure that we currently lack the capability to identify with our understanding of physics.”
Messier 4 star cluster, at its center is a medium-sized black hole. (Image: ESA/Hubble & NASA).
Black holes arise from the collapse of massive stars and grow by “gobbling up” gas, dust, stars, and other nearby black holes. Currently, known black holes tend to fall into one of two categories: stellar black holes, with masses ranging from a few to several tens of solar masses, and supermassive black holes, often referred to as “cosmic monsters”, which have masses ranging from millions to 50 billion times that of the sun.
Theoretically, medium-mass black holes, which range from 100 to 100,000 times the mass of the sun, are the most elusive black holes in the universe. While there are a few signs indicating their presence, no medium-mass black hole has yet been confirmed to exist.
This poses a puzzle for astronomers. If black holes grow from stellar size to supermassive through an insatiable consumption of their surroundings, then why do we not see them in this intermediate stage, when they are still developing? Or is this simply a limitation of humanity’s understanding of the universe, preventing us from detecting them?
To search for signs of a lurking medium-mass black hole, researchers directed the Hubble Telescope towards the Messier 4 cluster. This star cluster consists of tens of thousands to millions of densely packed stars, many of which are among the oldest stars ever formed in our universe.
There are 180 such globular clusters scattered throughout the Milky Way, and due to their high mass density in the central region, they serve as ideal locations for “young” black holes to continue growing.
Messier 4 is the closest globular cluster to Earth. Thanks to the Hubble and Gaia telescopes, researchers have gathered data over 12 years to accurately identify its stars and study their motion around the central region, discovering that the stars are moving around something massive that cannot be directly detected at the core of the cluster.
Astronomer Vitral noted that there is a small region of extremely high density, which is about three times less than the most dense mass ever detected by humans in other globular clusters.
The small area that researchers discovered is even smaller than anticipated, as the immense gravitational force could be generated by other dense dead stars, such as neutron stars and white dwarfs, and it could contain around 40 stellar black holes within a space equivalent to 1/10 of a light-year, resulting in an incredibly dense orbit of surrounding stars.
This leads to the possibility that they may merge and/or be ejected in a “game of pinball” among the stars.
To confirm the discovery of a medium-mass black hole without inadvertently uncovering new physical phenomena, researchers indicate that continued monitoring with the Hubble Telescope alongside the James Webb Telescope is necessary.
“Science rarely discovers something new in just a moment,” said scientist Timo Prusti from the Gaia telescope observatory, “and this could be another step in confirming that medium-mass black holes truly exist.”
