Two articles, one published in the journal “Nature” and one accepted for publication in the journal “Astronomy & Astrophysics”, report different aspects of a study of the galaxy GN-z11, one of the most distant known, which revealed the presence of the most distant and ancient black hole found so far. A team of researchers led by Roberto Maiolino of the University of Cambridge used the James Webb Space Telescope to examine GN-z11 finding traces of the activity of the supermassive black hole at its center. Those traces indicate that it’s devouring surrounding materials at a remarkable speed. Spectroscopic analyzes showed the presence of a clump of helium in the halo surrounding GN-z11 and no heavy elements, suggesting that first-generation stars may form in that halo.
The top image (NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (CfA), S. Tacchella (Cambridge), M. Rieke (University of Arizona), D. Eisenstein (CfA)) shows a portion of the sky photographed by the James Webb Space Telescope’s NIRCam instrument with the GN-z11 galaxy in the inset.
The discovery of the galaxy GN-z11 was announced in March 2016, achieved thanks to the use of the Hubble Space Telescope. A galaxy that we see as it was about 400 million years after the Big Bang could only arouse great interest among astronomers and was included among the targets of study with the James Webb space telescope within the JWST Advanced Deep Extragalactic Survey project (JADES).
The remarkable brightness of the galaxy GN-z11 was noted from the beginning and was attributed to a very high rate of star formation. Now the new observations finally possible with the James Webb Space Telescope show a slightly different situation in which there’s an active supermassive black hole, the most distant and consequently also the oldest discovered so far.
In particular, the NIRCam (Near-Infrared Camera) instrument was used to find signatures of the type generated by an accretion disk surrounding a supermassive black hole. This presence was also confirmed by spectroscopic indications obtained using the NIRSpec (Near-Infrared Spectrograph) instrument of ionized chemical elements that are typically present in those accretion disks.
The supermassive black hole seems even too big considering it’s at the center of a primordial galaxy. The mechanisms that lead to the birth of these black holes are at the center of various studies and the new information on the one at the center of the galaxy GN-z11 will be useful to test the various models proposed in recent years.
The researchers led by Roberto Maiolino used the NIRSpec instrument also to examine the composition of the GN-z11 galaxy well beyond its nucleus. The result was the discovery of a lump of helium in the halo surrounding it. This matches the researchers’ expectations, and the models indicate that clouds of gas that in primordial galaxies contain only hydrogen and helium could form first-generation stars.
The bottom image (NASA, ESA, CSA, Ralf Crawford (STScI)) shows the galaxy GN-z11 with spectroscopic detections of helium (He II) obtained with the James Webb Space Telescope’s NIRSpec instrument.
One of astronomers’ hopes is that the James Webb Space Telescope will be able to see far enough in space and time to spot traces of the oldest stars ever existed. This would be important to ascertain the level of precision of current models of the formation of the first stars and galaxies.
The researchers intend to continue the study of the galaxy GN-z11 with follow-up observations in the hope of finding traces of the formation of the first stars. A success would constitute a step forward in the reconstruction of a crucial phase in the history of the universe.
