Astronomers have discovered probably the heaviest black hole whose mass has been directly measured. This supermassive cosmic “monster” weighing 36 billion suns is located at the center of the galaxy, 6 billion light-years from the Solar System. The discovery was made by a Brazilian team of scientists led by Carlos R. Melo-Carneiro, using the unique gravitational lens known as the Cosmic Horseshoe.
What is the Cosmic Horseshoe?
This object is an example of almost perfect gravitational lensing. The galaxy LRG 3-757 in the foreground bends the light from a galaxy far behind it with its gravity, forming a bright arc — an Einstein ring, similar to a horseshoe. LRG 3-757 is a giant galaxy with a mass 100 times greater than that of the Milky Way. It is now known that an incredibly massive black hole is hidden in its heart.
How was the weight of a black hole measured?
It is extremely difficult to directly weigh such distant black holes. The team has taken a revolutionary approach by combining detailed data from the Very Large Telescope (VLT) and Hubble. They simultaneously simulated gravitational lensing, how the mass of the entire galaxy bends the Horseshoe’s light, and the movement of the stars in LRG 3-757. This combination made it possible to “weigh” the central black hole, obtaining an impressive figure of 36 billion solar masses.
This black hole is significantly beyond forecasts. The known relationship between the mass of the black hole and the velocity of the stars in the center of the galaxy suggested a lower mass for the velocity of stars of 366 km/s in LRG 3-757. The mass of the monster is 1.5 standard deviations higher than expected. This means that something unusual happened in the history of the galaxy, which led to the excessive growth of the black hole without a proportional increase in the speed of the stars.
Hypotheses about overweight
One of the reasons may be rapid mergers. LRG 3-757 could have formed from the merger of several large galaxies. As a result of the merger, their black holes joined together, and gravitational shocks threw some of the stars out, inflating the core. Another explanation is the powerful past activity of the core, when the black hole was an active quasar, powerful energy flows from it stopped the formation of stars and changed the structure of the galaxy. There is also a possibility that this is a “fossil quasar” – a relic of the early Universe, which gained mass incredibly quickly, absorbing matter, and the surrounding stars did not have time to evolve accordingly.
The discovery provides an extremely important example to the list of supermassive black holes that do not fit into existing theories. The uniqueness lies in the fact that we see LRG 3-757 as it was more than 4 billion years ago. This is one of the most massive black holes measured directly at such a huge distance.
Earlier we reported on the discovery of the heaviest neutron star in the Universe.
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