Sydney, Jun 16 (IANS): An international team of astronomers has discovered the fastest-growing black hole of the last nine billion years.

The black hole consumes the equivalent of one Earth every second and shines 7,000 times brighter than all the light from our own galaxy, making it visible to well-equipped backyard astronomers, said the team from the Australian National University (ANU).

Lead researcher Dr Christopher Onken from ANU described the black hole as a "very large, unexpected needle in the haystack".

"Astronomers have been hunting for objects like this for more than 50 years. They have found thousands of fainter ones, but this astonishingly bright one had slipped through unnoticed," Onken said.

The black hole has the mass of three billion suns. Others of a comparable size stopped growing so quickly billions of years ago.

"Now we want to know why this one is different -- did something catastrophic happen? Perhaps two big galaxies crashed into each other, funnelling a whole lot of material onto the black hole to feed it," Onken said.

The black hole has a visual magnitude of 14.5 - a measure of how bright an object appears to an observer on Earth.

This means anyone with a decent telescope in a very dark backyard can see it comfortably.

"It is 500 times bigger than the black hole in our own Galaxy," said co-author and ANU PhD researcher Samuel Lai.

"The orbits of the planets in our Solar System would all fit inside its event horizon -- the black hole's boundary from which nothing can escape."

A paper detailing the discovery has been submitted to the journal Publications of the Astronomical Society of Australia but has not yet been peer reviewed. A preprint version is available via the arXiv database.