‘Little red dots’ could herald the birth of supermassive black holes
Did cocoons of dense gas shine brightly in the early universe? The post ‘Little red dots’ could herald the birth of supermassive black holes appeared first on Physics World .
An international team of astronomers has discovered compelling evidence that newborn and rapidly growing supermassive black holes may be responsible for the mysterious "little red dots" observed throughout the early universe. This conclusion stems from the team's identification of a strong candidate for a new kind of object called a "black-hole star," which appears to power a little red dot dating back to just 660 million years after the Big Bang.
The team leader, Rohan Naidu of the University of Hawaii and MIT, describes these little red dots as "extraordinary objects" that likely contain a black-hole star within a dense gas cocoon, surrounded by a galaxy. While observing the distant universe using the James Webb Space Telescope (JWST) in 2022, astronomers were stunned to find numerous little red dots exhibiting high luminosity and unusual spectra, similar to stars but lacking X-ray emissions.
Previously, there was only circumstantial evidence supporting the hypothesis that these objects are black-hole stars. The JWST's observations, however, have provided concrete evidence for the existence of black-hole stars. One such example is MoM-BH*-1, an object shining 100 billion times brighter than any known star while outshining its host galaxy.
The object exhibits a unique phenomenon called the Balmer break, which is three to four times stronger than any previously observed, indicating the presence of a highly dense gas cocoon surrounding a 100,000 solar mass black hole.
The formation of this black hole and its surrounding cocoon is still a matter of debate. Some researchers propose that it originated from the direct gravitational collapse of a massive gas cloud, while others suggest it formed from the merger of massive stars. Naidu prefers the theory of a supermassive star birth, which could have occurred around 150 million years after the Big Bang when the universe was rich in hydrogen and helium.
Upon the star's death, it could have exploded in a supergiant star outburst, such as the one witnessed by the Eta Carinae in the 1840s, leaving behind a cocoon of gas and collapsing into a black hole star.
The discovery of MoM-BH*-1, the brightest known object, suggests that black-hole stars might be the origin of all supermassive black holes in the universe. As these objects erode their gaseous cocoon and accrete matter from it, radiation emitted by accretion can blow away the remaining cocoon. This scenario is supported by the recent detection of a little red dot from 11.8 billion years ago with X-rays starting to peak through the holes in its shredded cocoon.
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