GN-z11, found in the Ursa Major constellation, is a young yet sizeable galaxy that was first discovered in 2016. It is believed to have formed when the Universe was a mere 420 million years old, accounting for just 3 percent of its present age. Although GN-z11 is 25 times smaller than our Milky Way, it still possesses 1 percent of our Galaxy's stellar mass. A recent study has revealed that this galaxy is home to a black hole with a staggering 1.6 million solar masses.
Professor Roberto Maiolino from the University of Cambridge and his colleagues have discussed multiple theories to explain the formation of black hole seeds in the early Universe. These theories aim to account for the presence of incredibly massive black holes already observed at redshifts z=6-7.5. One of the most popular models is the direct collapse black holes, which involves the direct collapse of primordial clouds, potentially following the creation of a supermassive star. Other models consider the rapid merger of stars and black holes within dense nuclear star clusters, as well as accretion on Population III black hole seeds or even standard stellar remnants. Super-Eddington accretion has also been proposed as a possibility.
However, none of these models have been sufficiently tested due to the limitations of observing black holes with higher redshifts (z > 10) and lower masses (less than 10 million solar masses). This changed with the arrival of the NASA/ESA/CSA James Webb Space Telescope. In their study, Professor Maiolino and his team conducted a thorough analysis of GN-z11's spectrum. Initially detected by the Hubble Telescope, GN-z11 is the brightest galaxy with redshifts greater than 10 across all Hubble fields.
Astronomers used spectroscopic data obtained from Webb's Near-Infrared Spectrograph (NIRSpec) as part of the JADES survey to study GN-z11. The analysis revealed that the galaxy is dominated by an active galactic nucleus (AGN), indicating the presence of an accreting black hole. Although the contribution from extreme stellar populations cannot be ruled out, Wolf-Rayet stars alone are insufficient to explain many of the spectral properties.
As the first hyperluminous galaxy with high redshifts to be confirmed spectroscopically, GN-z11's AGN scenario offers a natural explanation for its exceptional luminosity. If this is indicative of other bright galaxies discovered at high redshifts by the Webb Telescope, it could suggest a more significant role for AGN in the reionization of the Universe.
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