The newly-discovered black hole resides in the hyperluminous galaxy GN-z11 at a redshift of 11 and could have originated from a stellar mass seed at redshifts 12 to 15.
The hyperluminous star-forming galaxy GN-z11 hosts an accreting black hole. Image credit: NASA / ESA / P. Oesch, Yale University / G. Brammer, STScI / P. van Dokkum, Yale University / G. Illingworth, University of California, Santa Cruz / Sci.News.
GN-z11 is a young but moderately massive galaxy located in the constellation of Ursa Major.
First discovered in 2016, this galaxy is estimated to date from when the Universe was only 420 million years old, or 3% of its current age.
GN-z11 is approximately 25 times smaller than our Milky Way and has just 1% of our Galaxy’s mass in stars.
Surprisingly, according to the new study, the galaxy hosts a black hole of about 1.6 million solar masses.
“Multiple theories have been proposed to describe the formation of black hole seeds in the early Universe and to explain the emergence of very massive black holes observed to be already in place at redshifts z=6-7.5,” said University of Cambridge’s Professor Roberto Maiolino and colleagues.
“Black holes resulting from the direct collapse of primordial clouds (possibly preceded by the formation of a supermassive star) into seeds with masses in the range of 10,000 to one million solar masses — the so-called direct collapse black holes — is one of the models most frequently invoked.”
“However, other models also consider rapid merging of stars and black holes in dense, nuclear star clusters, as well as accretion onto Population III black hole seeds or even normal stellar remnants.”
“Super-Eddington accretion has also been considered a possibility,” they added.
“Yet, none of these scenarios have been properly tested so far, as they required the observation of black holes at higher redshift (z > 10) and at lower masses (less than 10 million solar masses), which has been unfeasible until the advent of the NASA/ESA/CSA James Webb Space Telescope.”
In their study, Professor Maiolino and co-authors performed an extensive analysis of the spectrum of GN-z11.
“Initially detected with Hubble, this is the brightest galaxy at redshifts over 10 in all Hubble fields (including the totality of the CANDELS fields and Frontier Fields),” they said.
“Being three times more luminous than the characteristic luminosity of galaxies at z=7, if powered primarily by star formation, the implied density of luminous galaxies would be challenging to reconcile with many models of galaxy formation.”
The astronomers analyzed the spectroscopic data obtained with Webb’s Near-Infrared Spectrograph (NIRSpec) as part of the JADES survey.
The analysis of the NIRCam images revealed that the galaxy is dominated by an active galactic nucleus (AGN).
“GN-z11’s spectral features indicate that, in addition to star formation, the galaxy also hosts an accreting black hole,” the authors said.
“We do not exclude a contribution from extreme stellar populations, however, Wolf-Rayet stars alone cannot account for many of the spectral properties.”
“GN-z11 is the first of hyperluminous galaxies at high redshifts to be spectroscopically confirmed,” they added.
“The AGN scenario revealed by our analysis provides a natural explanation for the exceptional lumionsity of GN-z11.”
“If this is representative of the broader class of luminous galaxies discovered at high redshifts by Webb, then it would greatly alleviate the tension with models and simulations, and may suggest a stronger role of AGN in the reionization of the Universe.”
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Roberto Maiolino et al. 2023. A small and vigorous black hole in the early Universe. arXiv: 2305.12492
