Spotting the Galactic Nucleus

Indian researchers have discovered three supermassive black holes from three galaxies merging together to form a triple active galactic nucleus, a compact region at the centre of a newly discovered galaxy that has a much-higher-than-normal luminosity. This rare occurrence in our nearby universe indicates that small merging groups are ideal laboratories to detect multiple accreting supermassive black holes and increases the possibility of detecting such rare occurrences.

Supermassive black holes are difficult to detect because they do not emit any light. But they can reveal their presence by interacting with their surroundings. When the dust and gas from the surroundings fall onto a supermassive black hole, some of the mass is swallowed by the black hole, but some of it is converted into energy and emitted as electromagnetic radiation that makes the black hole appear very luminous. They are called active galactic nuclei (AGN) and release huge amounts of ionized particles and energy into the galaxy and its environment. Both of these ultimately contribute to the growth of the medium around the galaxy and ultimately the evolution of the galaxy itself.

A team of researchers from the Indian Institute of Astrophysics comprising Jyoti Yadav, Mousumi Das and Sudhanshu Barway, along with Francoise Combes of College de France, Chaire Galaxies et Cosmologie, Paris, while studying a known interacting galaxy pair, detected unusual emissions from the centre of one and a large, bright clump along the northern arm of another. According to the researchers, a major factor impacting galaxy evolution is galaxy interactions, which happen when galaxies move close to each other and exert tremendous gravitational forces on each other. During such galaxy interactions, the respective supermassive black holes can get near each other.

But, why is it important to study supermassive black holes at all? One pertinent question that goes round always is this: Do supermassive black holes cause galaxy rotation? If a black hole is in the centre of our galaxy, could it be the source of the rotation of the galaxy and if so, if it is accreting matter, could this mean that it is getting more and more massive? Wouldn't this imply that the rotation is getting faster and finally could this mean that a galaxy year is getting shorter even if it's just a little bit?

Black holes are among the most mysterious phenomena in the universe. Forged from the cores of dead stars, they are so dense that nothing can escape their gravitational pull, not even light, which renders them invisible. Entire stars, once luminous, can be extinguished if they cross a black hole's boundary, and pass the point of no return. Albert Einstein predicted more than a century ago, based on his theories untangling the nature of gravity, that such strange objects could exist, but he thought the idea was too far-fetched. In 1965, after Einstein's death, Penrose, the Oxford professor, published a paper showing, mathematically, that the forces of the universe could indeed produce black holes, and that inside their impenetrable depths resides something called a singularity, an inscrutable point which no known laws of physics can describe.

Such a thing might still seem too incredible to exist, but without black holes, the movements of faraway stars in our galaxy don't always make sense. Kudos to the young Indian minds doing this brilliant work!