Earlier this month, a team of researchers published a report in Nature describing a supermassive black hole (SMBH) dating to just 690 million years after the Big Bang. The discovery of such a massive object from when the Universe was a mere five percent of its current age may hold clues as to how SMBHs and early galaxies evolved.
“The quasar, J1342+0928, contains 800 million solar masses and shines 400 trillion times brighter than the Sun.”
Imagine a place in which time (as we understand it) no longer has any meaning. Now imagine the mass of millions or billions of suns concentrated into a volume smaller than a proton, from which nothing, not even light, can escape. Einstein refused to believe such things could exist, despite predicting them in his General Theory of Relativity. We’re talking about black holes, of course. Black holes dominate the Universe; we wouldn’t exist without them. Our Milky Way galaxy contains millions of black holes, and a new one is born about once a century.
Most black holes are formed when giant stars go supernova. Their cores collapse under their own gravity into single point of no dimension and infinite gravity, known as the singularity. No known laws of physics can predict the conditions inside a singularity; neither relativity, nor quantum mechanics, which are seemingly incompatible with each other, can be applied to a singularity.
But the really large black holes, appropriately called supermassive black holes, sit at the center of most galaxies, including our own (estimates of the number of galaxies in the known Universe range from 100 billion to two trillion). Supermassive black holes contain millions to billions of times the mass of our Sun. The Milky Way’s central SMBH, Sagittarius A*, weighs in at four million solar masses. Although the origins of stellar-mass black holes are well-understood, the formation of SMBHs remains of the biggest mysteries in cosmology.
Quasars in the early Universe may help solve this problem.
Peering deep into the Universe is a journey back in time. SMBHs in the centers of young galaxies 13 billion years ago weren’t dark and quiet like they are today. In the early Universe, the centers of galaxies were wild and violent places. As their SMBHs grew by swallowing everything from dust to entire stars, they emitted titanic amounts of energy. As matter rapidly fell into a black hole, huge jets of cosmic rays were blasted into space for millions of years. Galaxies with active central supermassive black holes that emit these jets, which are thousands of light-years long, are known as quasars.
Quasars are the brightest objects in the Universe, often outshining their home galaxies by a factor of 1000. This is a result of friction from matter swirling around and falling into a black hole, in a zone known as an accretion disk. In the accretion disk, particles of matter are heated to millions of degrees as they whip around the black hole at nearly the speed of light. Once all the matter in the accretion disk is consumed, the quasar turns off. This process typically lasts 100 million to one billion years.
Quasars emit truly unimaginable amounts of energy. “This quasar has a bolometric luminosity of 4 × 1014L⊙ and a black hole mass of 8 × 108M⊙,” lead researcher Eduardo Bañados of The Observatories of the Carnegie Institution for Science, wrote in his report. The quasar, J1342+0928, contains 800 million solar masses and shines 400 trillion times brighter than the Sun. Figuring out how quasars grew so large so fast will help scientists explain how early galaxies formed.
How could a black hole grow so much so quickly? Quasars harbor clues.
When typical black holes form, it generally contains 50-100 solar masses and then grows as it consumes anything that strays too close. The problem facing cosmologists, however, is how a SMBH can become so massive in a (relatively) small amount of time.
“If you make it grow, feed it material like gas from its surroundings and let it grow for 690 million years, you wouldn’t be able to reach the size of this supermassive black hole,” Bañados explains in his report. “These are the quasars that currently place the strongest constraints on early black hole growth.”
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