Artist's illustration of a supermassive black hole at the center of a galaxy. / NASA/JPL-Caltech
An international team with the participation of the Spanish National Research Council (CSIC) has discovered supermassive black holes in dwarf galaxies when the Universe was much younger than it is today, 6,000 million years after the Big Bang. This is a very unusual finding since until now very few cases have been discovered in the local Universe – the Universe today (13.6 gigayears after the Big Bang). The study has been published in The Astrophysical Journal Letters.
Supermassive black holes have masses of more than 1 million suns. Every massive galaxy is believed to contain a supermassive black hole at its centre. For example, the one at the centre of the Milky Way is called Sagittarius A and has a mass equivalent to about 4 million suns. Smaller, less massive dwarf galaxies should contain intermediate-mass black holes, smaller than 1 million suns. For a couple of decades, hundreds of intermediate-mass black holes have been located in dwarf galaxies of the local universe thanks to their active galactic nucleus (AGN), since the matter around black holes emits radiation when these are active.
This study presents a sample of seven dwarf galaxies more distant than in most cases, between 10 and 6 billion years after the Big Bang. "What has surprised the team is that their mass is consistent with the mass of supermassive black holes, since they are 10 million and 100 million times the mass of the Sun," says Mar Mezcua, first author of the study and researcher at the Institute of Space Sciences (ICE-CSIC) and the Institute of Space Studies in Catalonia (IEEC).
Massive galaxies and their super-strong black holes are believed to grow at the same time, they coevolve. For this reason, this new finding suggests that black holes have grown faster than their host galaxies. The research team hypothesizes that, over time, these galaxies will grow until their mass matches the one of the black hole they host.
Furthermore, the team concludes that these black holes may originate from dwarf galaxies with intermediate-mass black holes in the early universe, 1 billion years after the Big Bang. Researchers have come to this conclusion after running simulations of intermediate-mass black holes or seed black holes (from which supermassive black holes are supposed to grow) and discovering that possibly some of those intermediate-mass black holes have rapidly evolved to become supermassive, unlike their host galaxies.
"This finding has implications for our understanding of the growth of supermassive black holes, such as the black hole at the centre of the Milky Way," says the astronomer.
With the new generation of telescopes, such as DESI or LSST, it is expected that many more dwarf galaxies even more distant will be detected, which will allow further investigation of the evolution of black holes from the first seeds to supermassive black holes.
ICE-CSIC Communication /CSIC Communication
Mar Mezcua, Malgorzata Siudek, Hyewon Suh, Rosa Valiante, Daniele Spinoso and Silvia Bonoli. Overmassive black holes in dwarf galaxies out to z̴̴̴~0.9 in the VIPERS survey. The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/acae25.