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Chandra tags ancient black holes

‘Growing like gangbusters’

By Richard Chirgwin, 15 Jun 2011

Black holes may have been all over the early universe, according to new findings announced by NASA.

A starfield gathered by its Chandra X-ray observatory, known as Chandra Deep Field South (CDFS), and analyzed in conjunction with the Hubble Space Telescope, has turned up a mass of previously-undiscovered black holes from when the universe was around 800 to 950 million years old. These black holes, says the study’s lead author Ezequiel Triester of the University of Hawaii, are “growing like gangbusters”.

The sources discovered by the CFDS were identified by the luminous jets emitted by matter falling into the black holes, similar to quasars but a hundred times fainter. This leads NASA to estimate that the black holes causing the jets are a thousand times less massive than those in quasars.

Hidden in dust clouds, the black holes (or rather, their giveaway luminous jets) could not be detected by optical telescopes, which is why Chandra was brought into play. Those same jets emit X-rays along with light, both of which are red-shifted. That red shift (the emitted radiation is observed at a lower frequency than it’s emitted at) identifies the speed at which the galaxies are receding from us, yielding the estimate of their age.

NASA estimates that there may have been as many as 30 million supermassive black holes in the early universe – making them ten thousand times more common than had previously been estimated.

The study suggests that the very young black holes grew quickly, in tandem with the galaxies that host them. In other words, the symbiotic relationship between black holes and more contemporary galaxies could have existed since the earliest days of galactic evolution.

The age of the black holes observed in CDFS is measured by the red-shift (that is, the amount by which their emitted radiation is shifted towards lower frequencies, because of the speed at which the galaxies are receding from us).

It’s possible that these ancient black holes may lie at the heart of all early galaxies, meaning that there’s millions more yet to be found.

Triester’s findings are published in Nature today, June 16. ®

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