Enigmatic black hole: X-rays from the dawn of time

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  • Published: Mar 1, 2015
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Enigmatic black hole: X-rays from the dawn of time

Ancient and ultraluminous

artist's impression of a quasar with a supermassive black hole in the distant universe. Credit: Zhaoyu Li/NASA/JPL-Caltech/Misti Mountain Observatory

An ancient black hole that formed less than a billion years after the Big Bang sits at the heart of a distant quasar first observed from China. The black hole has a mass estimated at 12 billion times that of our Sun and the system a luminosity equivalent to 420 trillion suns. The Hubble and Chandra X-ray telescopes are now observing this astonishing and enigmatic entity.

An international team led by astronomers from Peking University, China and from the University of Arizona, USA, reported details of the quasar - SDSS J0100+2802 - in the journal Nature. The work marks an important step in understanding how quasars, the most energetic objects in the universe, have evolved from the earliest epoch, a mere 900 million years after the Big Bang occurred 13.7 billion years ago.

Size is everything

One of the co-authors of the paper, Xiaohui Fan, Regents' Professor of Astronomy at the University of Arizona's Steward Observatory, points out that despite all the team have discovered about the system, the discovery of this ultraluminous quasar represents something of an enigma to astronomy. Namely, how could such a large black hole have grown when the universe was so young, conventional theories of black hole formation suggest this object should not exist.

"How can a quasar so luminous, and a black hole so massive, form so early in the history of the universe, at an era soon after the earliest stars and galaxies have just emerged?" Fan asks. "And what is the relationship between this monster black hole and its surrounding environment, including its host galaxy?" Regardless, the ultraluminous quasar and its supermassive black hole offer astronomers a unique cosmic laboratory in which they can examine mass assembly and galaxy formation around the most massive black holes in the early universe and unravelling this enigma may provide important clues to improve our understanding of the early years of the universe.

The quasar dates from a time close to the end of an important cosmic event that astronomers referred to as the "epoch of reionization". This was the cosmic dawn when the fusion furnaces of the first stars were fired up, it is thought to have ended the "cosmic dark ages" and transformed the universe into something resembling what we see each night when we point out telescopes skyward.

Quasars, quasars everywhere

Quasars were first identified in 1963 as highly energetic entities across deep space. They spew out vast quantities of energy and are now known to house a supermassive black hole at their centre that pulls in matter from its surroundings. The recent digital sky surveys, such as the Sloan Digital Sky Survey, have helped astronomers identify more than 200,000 quasars, some of which existed just 700 million years after the Big Bang. However, this newly studied quasar is seven times brighter than the most distant, most red shifted, quasar known, which is 13 billion light years from Earth.

Our Milky Way galaxy has a massive black hole at its centre, but it is miniscule in comparison to those at the heart of quasars, and in particular the ultraluminous quasar, having a mass just 4 million times that of the Sun. The new quasar is 3000 more massive than our galactic black hole, Fan points out.

Doctoral student Feige Wang who works under Fan and Xue-Bing Wu at Peking University was first to catch sight of the quasar. "This quasar was first discovered by our 2.4-metre Lijiang Telescope in Yunnan, China, and we're very proud of it," Wang says. "The ultraluminous nature of this quasar will allow us to make unprecedented measurements of the temperature, ionization state and metal content of the intergalactic medium at the epoch of reionization."

Once the quasar ha d been detected, two bigger telescopes in southern Arizona were charged with the task of determining its distance and its mass. The 8.4-metre Large Binocular Telescope, or LBT, on Mount Graham and the 6.5-metre Multiple Mirror Telescope, or MMT, on Mount Hopkins did the heavy lifting. The observations were confirmed by the 6.5-metre Magellan Telescope in Las Campanas Observatory, Chile, and the 8.2-metre Gemini North Telescope in Mauna Kea, Hawaii.

"This quasar is unique," explains Wu. "Just like the brightest lighthouse in the distant universe, its glowing light will help us to probe about the early universe." Wu leads a team that has developed a technique for single out quasars in the distant universe using optical and near-infrared (NIR) photometric data from the Sloan Digital Sky Survey and NASA's Wide-Field Infrared Explorer, or WISE, satellite. "The especially sensitive optical and infrared spectrographs of the LBT provided the early assessment of both the distance of the quasars and the mass of the black hole at the quasar's centre," Fan explains. The next step will be to turn the Hubble space telescope's attention on the quasar and to begin exploring it in X-ray light with the Chandra X-ray Telescope.

Related Links

Nature 2015, 518, 512-515: "An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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