New Delhi: The James Webb Space telescope has discovered hundreds of compact, luminous objects in the early universe dubbed Little Red Dots (LRDs), that
have defied explanation. At the 247th meeting of the American Astronomical Society in Phoenix, Arizona, astronomers proposed that these mysterious objects are likely to be gigantic short-lived stars rather than star forming galaxies or active black holes. LRDs have puzzled scientists since they were first discovered in deep-field images captured by Webb in 2022. Earlier telescopes such as Hubble could not resolve them, but Webb’s infrared instruments revealed their extreme redness from cosmic expansion and high redshifts.
Webb also revealed their distinctive spectra. These were high luminosity, with a V-shaped continuum with a strong Balmer break, and broad hydrogen emission lines, lacking metal features or X-ray emissions. Previous interpretations invoked complex scenarios with accreting black holes, dusty accretion disks, obscured galactic nuclei and even dark stars powered by annihilation of dark matter rather than nuclear fusion. All of these proposals struggle to explain all the observed spectral features simultaneously, without multi-component assumptions. The researchers developed a detailed physical model for a metal-free or Population III supermassive star, rapidly accumulating mass through accretion of gas in pristine halos.
Research explains early supermassive black holes
In the simulations, these stars grew very massive, containing up to one million times the mass of the Sun, by quickly scooping up the pure gas in the early universe. The simulations indicated that the light from such stars perfectly match the LRDs seen by JWST, with a big jump in blue light and strong hydrogen emission lines. This blue light has been stretched out to red wavelengths because of the expansion of the universe, resulting in their characteristic colour today. The brightest ones shine intensely for a few hundred or thousand years, before collapsing into seeds of giant black holes. This explains how supermassive black holes formed so rapidly in the early universe as well.
