Quasars — supermassive black holes found at the centre of distant massive galaxies — are the most luminous beacons in the sky. These central supermassive black holes actively accrete the surrounding materials and release a huge amount of their gravitational energy.
On Wednesday 25 February, Astronomers say they have discovered a black hole so big that it challenges the theory about how they grow. This black hole was formed about 900 million years after the Big Bang. But with measurements indicating it is 12 billion times the size of the sun, the black hole challenges a widely accepted hypothesis of growth rates.
The quasar (named SDSS J0100+2802) was found at a redshift of z = 6.30. This is a measurement of how much the wavelength of light emitted from it that reaches us on Earth is stretched by the expansion of the universe. As such, it can be used to calculate the quasar’s age and distance from our planet. A higher redshift means larger distance and hence looking further back in time.
“Based on previous research, this is the largest black hole found for that period of time,” Fuyan Bian, Research School of Astronomy and Astrophysics, Australian National University (ANU), said.
“Current theory is for a limit to how fast a black hole can grow, but this black hole is too large for that theory.”
Black holes grow, scientific theory suggests, as they absorb mass. However, as mass falls toward the black hole, it will be heated, creating radiation pressure, which pushes the mass away from the black hole. “Basically, you have two forces balanced together which sets up a limit for growth, which is much smaller than what we found,” said Bian.
The quasar was spotted by telescopes in China, Hawaii, Arizona and Chile, and studied by a team of astronomers from around the world. But it’s discoverers aren’t entirely sure how it grew so big, so fast.
US co-author Dr Yuri Beletsky, from the Carnegie Institution in Washington DC, said: “This quasar is a unique laboratory to study the way that a quasar’s black hole and host galaxy co-evolve. “Our findings indicate that in the early universe, quasar black holes probably grew faster than their host galaxies, although more research is needed to confirm this idea.”
Professor Yuri and his team have many follow-up observations planned for the coming year, including projects using space telescopes such as Hubble to get an even better look at things in and near this impressive quasar’s galaxy.