On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist's illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. New studies with data from Chandra and several other telescopes have determined the black hole's spin, mass, and distance with unprecedented accuracy.
According to a new report, dark matter may form supermassive black holes.
A new theoretical study has proposed a novel mechanism for the formation of supermassive black holes from dark matter. The international team discovered that, rather than the conventional formation scenarios involving ‘normal’ matter, supermassive black holes could form directly from dark matter in high density regions in galaxies’ centres. The findings, which have important implications for cosmology in the early Universe, have been published in the Monthly Notices of the Royal Astronomical Society.
One of the most difficult problems in the study of galaxy evolution today is determining how supermassive black holes first formed. There have been observations of supermassive black holes as early as 800 million years after the Big Bang, with little explanation for how they could evolve so rapidly.
Normal baryonic matter – the atoms and elements that make up stars, planets, and all visible objects – collapses under gravity to form black holes, which then grow over time, according to standard formation models. The new research, however, looks into the possibility of stable galactic cores made of dark matter and surrounded by a diluted dark matter halo, and discovers that the centres of these structures can become so concentrated that they can collapse into supermassive black holes once a critical threshold is reached.
According to the model, this could have happened much faster than other proposed formation mechanisms, allowing supermassive black holes to form before the galaxies they inhabit in the early Universe, contrary to current understanding.
“This new formation scenario may offer a natural explanation for how supermassive black holes formed in the early Universe, without requiring prior star formation or invoking seed black holes with unrealistic accretion rates,” says Carlos R. Argüelles, the researcher at Universidad Nacional de La Plata andICRANet who led the investigation.
Another intriguing result of the new model is that the critical mass for black hole collapse may not be reached for smaller dark matter halos, such as those surrounding some dwarf galaxies. The authors speculate that this could result in smaller dwarf galaxies with a central dark matter nucleus instead of the expected black hole. A dark matter core could still mimic the gravitational signatures of a traditional central black hole, while the dark matter outer halo could also explain observed galaxy rotation curves.
“This model shows how dark matter haloes can have dense concentrations at their centres, which may be important in understanding the formation of supermassive black holes,” Carlos added.
“We’ve shown for the first time that such core-halo dark matter distributions can form in a cosmological framework and remain stable throughout the Universe’s lifetime.”
The authors hope that future research will shed more light on the formation of supermassive black holes in the very early days of our Universe, as well as whether the centres of non-active galaxies, including our own Milky Way, may be home to these dense dark matter cores.