When the James Webb Space Telescope (JWST) examined some of the darkest regions of the sky, it detected objects fainter and more distant than any seen before. Among them were the mysterious Little Red Dots (LRDs): reddish, point-like sources observed when the Universe was only a billion years old.
A new study in Nature argues that these objects are young, overmassive black holes—possible starting points for the galactic black holes and quasars that appeared surprisingly early in cosmic history.
A puzzle in the early Universe
Astronomers initially considered LRDs to be young, powerful active black holes, perhaps the seeds of the first galaxies. Yet active black holes typically produce strong radio and X-ray emission, as quasars do, while LRDs do not.
Another possibility was that LRDs were extremely large progenitor stars made primarily of hydrogen and helium. Their spectra resemble models of the first stars, but they also display a strong rotational Doppler shift. The apparent rapid rotation would be unusual for such primordial stars.
Collapse inside a proto-galaxy
The study investigated the mystery through computer simulations of the early Universe. The researchers modeled a proto-galaxy embedded in the young cosmos and followed how its environment influenced galactic evolution.
In the simulations, gas clouds inside the proto-galaxy were exposed to intense ultraviolet light. This radiation prevented the clouds from fragmenting into the smaller structures that normally become stellar nurseries. Instead, the giant clouds collapsed into a primordial superstar, which then rapidly collapsed into a black hole.
The resulting black holes began with masses on the order of a million Suns. Radiation in the surrounding early-Universe environment then helped drive additional gas toward them, allowing rapid growth.
Growth beyond the usual limit
Ordinarily, a black hole’s growth is constrained by the heat and light produced as it consumes matter. That radiation pushes against infalling material. The balance between gravitational attraction and this outward pressure is called the Eddington Limit.
In the simulated environment, however, external radiation helped force material inward. The black holes could therefore consume matter at a super-Eddington rate, accelerating their growth beyond the usual balance point.
A model matching JWST observations
The simulated overmassive black holes produced spectra that strongly matched the observed spectra of LRDs. This offers an explanation for why the objects show characteristics associated with both black holes and primordial stars.
The study’s model also provides a possible account of why supermassive black holes existed so early in the Universe. Within this interpretation, Little Red Dots are the seeds from which galactic black holes and powerful quasars can develop.
Original source: universetoday.com
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