An artist’s illustration of a supermassive black hole weighing millions to billions of times the mass of our Sun. Image: NASA/JPL-Caltech
New Delhi: Supermassive black holes at the centres of galaxies are known to give rise to fast-moving relativistic[footnote]I.e. moving nearly at the speed of light[/footnote] jets of particles that can traverse large distances through the galaxy, and beyond. The jets have long been suspected of driving the evolution of galaxies – but this has remained a suspicion thus far.
A new study by an international team of astronomers, including Dipanjan Mukherjee of the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, has unravelled the mystery. The team has shown that even a relatively weak jet from a supermassive black hole can clear the nuclear region of the galaxy of its gas, indicating that it could have an essential role in the evolution of its host galaxy.
Mukherjee’s team observed the motions of molecular gas in a galaxy called B2 0258+35, using the Northern Extended Millimetre Array, or NOEMA, telescopes in France.
The team included Suma Murthy, Raffaela Morganti and Tom Osterloo from the Netherlands Institute for Radio Astronomy; Pierre Guillard from the Institut d’Astrophysique de Paris; Alexander Wagner from the University of Tsukuba, Japan; and Geoffrey Bicknell from the Australian National University.
Their paper was published in February 2022.
An IUCAA press release that announced the findings said the astronomers found gas being steadily blown away from the galaxy’s central regions, pushed by a relativistic jet. Although the power of the jet observed in radio wavelengths was moderate, it was found to still be capable of clearing out nearly 75% of the central gas reservoir.
It is reportedly the first unambiguous detection of a relativistic jet from a supermassive black hole removing the gas in a galaxy. The researchers have apparently also ruled out competing explanations for the gas outflow.
“The ejected gas is, however, not fast enough to completely escape the galaxy, and will eventually fall back in,” the release added.
According to the research team, the findings are significant because even while relativistic jets from supermassive black holes have long been suspected of driving the evolution of galaxies, scientists have thus far only considered their heat impact on the circum-galactic atmosphere.
Numerical simulations conducted earlier by Mukherjee and his colleagues predicted that such jets would strongly influence the host galaxy. But they didn’t have proof.
Observations with telescopes had found signatures of jets injecting energy into the interstellar medium of galaxies (i.e. the space between galaxies). However, their effects couldn’t be separated from the effects of the radiation from the central black hole.
“The new results from this study provide definitive proof that relativistic jets can indeed substantially affect the host galaxy’s gas,” the IUCAA press release said. “This may have a significant impact on how and over what timescales stars are formed in such galaxies, which are topics of active current research.”
It also noted that lower power jets, such as the present one, are more common than their higher power counterparts. This study is also reportedly significant for showing a synergy between the observed data and the researchers’ simulations, conducted in 2018.
This article has been republished from India Science Wire.