The hungriest known black hole in the early universe has been found, thanks to teamwork between NASA's James Webb Space Telescope (JWST) and Chandra X-ray Observatory.
The black hole's voracious appetite, which has allowed it to pile on more than seven million solar masses in just 12 million years, exceeds the theoretical maximum growth rate and goes some way to explaining how black holes could grow so massive so quickly in the early universe.
"This black hole is having a feast," study co-author Julia Scharwächter, of the International Gemini Observatory, said in a statement.
The early black-hole mass problem has vexed astronomers for years. JWST, and the Hubble Space Telescope before it, have discovered galaxies containing black holes with hundreds of millions, and sometimes even billions, of solar masses in the early universe. How these black holes formed and grew so massive so quickly has, however, remained unexplained. Now, thanks to the JWST and Chandra, we've seen one of these black holes in the act of growing fat.
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The black hole — cataloged as LID-568, and which we're seeing as it existed just 1.5 billion years after the Big Bang — was first spotted in a Chandra survey of luminous X-ray-emitting objects in the distant universe. X-rays are a byproduct of gas being gravitationally pulled onto a black hole, and when that gas cannot be swallowed all at once, it bunches up in a disk that grows hot enough to emit X-rays. The faster the rate of accretion, the greater the energy of the X-rays.
However, there's supposedly a theoretical limit to the amount that a black hole can consume at any one time. It's called the Eddington limit, after the British astrophysicist Sir Arthur Eddington, and describes a balance between the rate of infalling matter onto a black hole and the amount of radiation (including X-rays) produced by the infall that then pushes back on the accreting matter. We call this process feedback, and above a certain rate of accretion, the feedback grows so great that it shuts the accretion down. This is the Eddington limit.
When astronomers led by the International Gemini Observatory's Hyewon Suh followed up on LID-568 with JWST's Integral Field Spectrograph instrument, they measured outflows from the black hole moving at 500 to 600 kilometers (310 to 370 miles) per second. Coupled with the X-rays being much brighter than what we would expect for an accreting black hole so relatively early in cosmic history, this level of feedback is calculated to be 40 times greater than the Eddington limit.
So is this black hole breaking the laws of physics?
Not necessarily. Such "super-Eddington" accretion can be maintained for a short time before the feedback blows away the black hole's food, and indeed super-Eddington accretion has been observed before and had even been proposed as a mechanism by which supermassive black holes grew so massive so quickly. LID-568 is, however, the best and clearest example yet found.
"This extreme case shows that a fast-feeding mechanism above the Eddington limit is one of the possible explanations for why we see these very heavy black holes so early in the universe," said Scharwächter.
The black hole would have originally begun life as a "seed." Various mechanisms could in theory produce these seeds, such as massive stars leaving behind stellar-mass black holes when they die (these would be "light" seeds), or the direct gravitational collapse of a massive gas cloud to form an intermediate thousand-or-so solar mass black hole (these would be "heavy" seeds). Modeling by Suh and Scharwächter's team found that LID-568 probably began life as a "light" 100-solar-mass black hole and began this episode of accretion 12 million years earlier, while it sat at the center of a giant molecular gas cloud that the black hole is consuming in its entirety.
"The discovery of a super-Eddington accreting black hole suggests that a significant portion of mass growth can occur during a single episode of rapid feeding, regardless of whether the black hole originated from a light or heavy seed," said Suh.
This one rapid burst of accretion won't continue forever; the Eddington limit will eventually prevail. Currently, LID-568 stands at 7.2 million times the mass of the sun, compared to the 4.1-million-solar-mass of Sagittarius A*, which is the black hole at the center of our Milky Way galaxy. However, super-Eddington accretion can be episodic — the heated gas that has been blown away could cool and gradually fall back onto the black hole. LID-568 may be finishing its dinner, but dessert could be just around the corner.
The new study was published online Monday (Nov. 4) in the journal Nature Astronomy.
