The discovery of the second-most distant – and thus second oldest – quasar ever detected may force a rethink of how black holes grow.
Pōniuāʻena, which means “unseen spinning source of creation, surrounded with brilliance” in the Hawaiian language, is more than 13 billion light-years from Earth – a cosmological redshift greater than 7.5.
Only a quasar still just known as J1342+0928, detected in 2017, is more distant.
Spectroscopic observations from the WM Keck Observatory and Gemini Observatory on Maunakea, in Hawaii, show that Pōniuāʻena (also known as J1007+2115) hosts a black hole that is 1.5 billion times more massive than our Sun.
It is the most distant known object hosting a black hole exceeding one billion solar masses, says Jinyi Yang, from the University of Arizona, lead author of a paper in Astrophysical Journal Letters, currently available on the preprint server ArXiv.
Black holes, the most luminous objects in the Universe, grow by accreting matter. In the standard picture, supermassive black holes grow from a much smaller “seed” black hole, which could have been the remnant of a massive star that died.
For a black hole of this size to form so early in the Universe, the researchers say, it would need to have started as a 10,000-solar-mass seed black hole only 100 million years after the Big Bang.
“How can the Universe produce such a massive black hole so early in its history?” says co-author Xiaohui Fan, also from the University of Arizona. “This discovery presents the biggest challenge yet for the theory of black hole formation and growth in the early Universe.”
Current theory holds that the birth of stars and galaxies as we know them started during the Epoch of Reionisation. Beginning about 400 million years after the Big Bang, the diffuse matter in between galaxies went from being neutral hydrogen to ionized hydrogen. The growth of the first giant black holes is thought to have occurred during this time.
The discovery of quasars like Pōniuāʻena is a big step towards understanding this process of reionization and the formation of early supermassive black holes and massive galaxies, the researchers say.
“Pōniuāʻena acts like a cosmic lighthouse,” says Joe Hennawi, from the University of California, Santa Barbara. “As its light travels the long journey towards Earth, its spectrum is altered by diffuse gas in the intergalactic medium which allowed us to pinpoint when the Epoch of Reionisation occurred.”
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