How the most distant black hole ever could rewrite the history of the universe

Contributed by
Dec 10, 2017

Supermassive black holes lurk in every galaxy. As if their voracious appetite for matter and insane gravitational forces weren’t enough to make them as fascinating as they are terrifying, this one could tear apart everything we think we know about the early universe.

The monster was discovered by astronomers using the NASA Wide-field Infrared Survey Explorer (WISE), who combined that data to figure out which objects they could potentially focus on before a team at Carnegie Observatories, led by Eduardo Bañados, selected those that would be worth a second look with Carnegie’s Magellan Telescope. Somewhere among hundreds of millions of potential subjects was a quasar so vast and so anomalous that it demanded more attention.

"This black hole grew far larger than we expected in only 690 million years after the Big Bang, which challenges our theories about how black holes form," said Daniel Stern of NASA's Jet Propulsion Laboratory, a co-author of the study recently published in Nature.

Quasars blaze from some of the furthest reaches of the cosmos. As some of the brightest objects in space whose light takes billions of years to reach Earth, they could elucidate the mysteries of what exactly happened as the universe began to evolve, since we are observing them as they were when planets and stars were just emerging.


Binary quasars imaged by Hubble in 2014. Credit: NASA

It was the mostly neutral hydrogen around this beyond-ancient quasar that told Bañados and his team that they had found something extraordinary. Cosmic inflation (which is thought to have started a fraction of a second after the Big Bang) was the period during which a mass of hot particles spread through the darkness unbelievably fast, possibly because of repulsive gravity, until they cooled down and formed an immense cloud of neutral hydrogen gas 400,000 years later. When gravity caused matter to coalesce into stars and galaxies, they spewed enough energy to excite the neutral hydrogen into losing an electron—ionizing. Reionization allowed photons to shoot through infinite space and light up the universe.

Seeing the quasar surrounded by hydrogen as it was before, or maybe just on the brink of, reionization means it is the only relic from that dark period that astronomers have ever found.

The team determined how far away it is by its redshift, the measurement of how much the expansion of the universe has stretched the wavelength of radiation emitted by a celestial body before that light reaches our planet. Higher redshifts translate to greater distances from Earth and glimpses further back in time (depending on how long that light took to travel to us). This quasar’s redshift of 7.54 means its light took 13 billion years to reach us.

“The existence of this supermassive black hole when the Universe was only 690 million years old, just five per cent of its current age, reinforces early models of black hole growth that allow black holes with [greater] initial masses,” Bañados and his colleagues said. If black holes started off with more mass, it could explain the existence of one that was already so massive at such an early stage of cosmic evolution.

This was totally worth the 13-billion-year wait.

(via NASA)

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