All Entries Tagged With: "Australian Astronomical Observatory"
Galactic explosion betrays black hole
TWO MILLION YEARS AGO a supermassive black hole at the heart of our galaxy erupted in an explosion so immensely powerful that it lit up a cloud 200,000 light years away, a team of researchers led by the University of Sydney has revealed.
The finding is an exciting confirmation that black holes can ‘flicker’, moving from maximum power to switching off over, in cosmic terms, short periods of time.
An artist’s conception of a black hole generating a jet. Two million years ago the supermassive black hole at the centre of our Galaxy was 100 million times more powerful than it is today. Credit: NASA / Dana Berry / SkyWorks Digital
“For 20 years astronomers have suspected that such a significant outburst occurred, but now we know when this sleeping dragon, four million times the mass of the Sun, awoke and breathed fire with 100 million times the power it has today,” said Professor Joss Bland-Hawthorn from the University’s School of Physics, and lead author of an article on the research to be published in The Astrophysical Journal.
Professor Bland-Hawthorn unveiled the research at the international Galaxy Zoo science conference on 24 September in Sydney.
“It’s been long suspected that our Galactic Centre might have sporadically flared up in the past. These observations are a highly suggestive ‘smoking gun’,” said Martin Rees, Astronomer Royal, who was one of the first scientists to suggest that massive black holes power quasars.
Fossil record
The evidence for the findings comes from a lacy filament of hydrogen gas called the Magellanic Stream. It trails behind our galaxy’s two small companion galaxies, the Large and Small Magellanic Clouds.
“Since 1996, we’ve been aware of an odd glow from the Magellanic Stream, but didn’t understand the cause. Then this year, it finally dawned on me that it must be the mark, the fossil record, of a huge outburst of energy from the supermassive black hole at the centre of our galaxy.”
The region around the galaxy’s supermassive black hole and the black hole is called Sagittarius A* (pronounced Sagittarius A-star). It emits radio, infrared, ultraviolet, x-ray and gamma ray emissions. Flickers of radiation rise up when small clouds of gas fall onto the hot cloud of matter that swirls around the black hole.
The video below show a computer simulation of a black hole in real time showing how gas falling in forms a disc that spins around the black hole. The friction causes the gas to become so hot it produces beams of UV radiation. Credit: McKinney (UMD), Tchekhovskoy (Princeton), Blandford (KIPAC), Kaehler (KIPAC)
In stark contrast to this current inactivity, evidence is emerging that there was a cataclysmic event in the past.
“In particular, in 2010 NASA’s Fermi satellite discovered two huge bubbles of hot gas billowing out from the centre of the galaxy, covering almost a quarter of the sky,” said Professor Bland-Hawthorn.
On-and-off black holes
Earlier this year, computer simulations of the Fermi bubbles made by the University of California Santa Cruz controversially suggested that they were caused by a colossal explosion from Sagittarius A* within the last few million years.
“When I saw this research I realised that this same event would also explain the mysterious glow that we see on the Magellanic Stream,” Professor Bland-Hawthorn said.
“Together with Dr Ralph Sutherland from Mount Stromlo Observatory and Dr Phil Maloney, from the University of Colorado, I calculated that to explain the glow it must have happened two million years ago because the energy release shown by the Santa Cruz group perfectly matched, to our delight, that from the Magellanic Stream.”
“The galaxy’s stars don’t produce enough ultraviolet to account for the glow, nor could they have in the past,” said Dr Maloney. “The Galactic Centre never formed stars at a high enough rate. There had to be another explanation.”
Professor Bland-Hawthorn said, “In fact the radiation from stars is one hundred times too little to account for the radiation now or at any time. The galaxy could never have produced enough UV radiation to account for it. So the only explanation was it had to be produced from our dragon, the massive black hole.”
“The realisation that these black holes can switch on and off within a million years, which given the universe is 14 billion years old means very rapidly, is a significant discovery.”
Will such a colossal explosion ever happen again?
“Yes, absolutely! There are lots of stars and gas clouds that could fall onto the hot disk around the black hole,” says Professor Bland-Hawthorn. “There’s a gas cloud called G2 that astronomers around the world are anticipating will fall onto the black hole early next year. It’s small, but we’re looking forward to the fireworks!
Professor Bland-Hawthorn is a Fellow of the Australian Astronomical Observatory.
Adapted from information issued by the University of Sydney.
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Australia’s night sky – amazing time-lapse film
A NEW TIME-LAPSE VIDEO has captured the beauty of the night sky above the Anglo-Australian Telescope at Siding Spring Observatory in eastern Australia.
It was made by astronomy research fellow Dr Ángel López-Sánchez (Australian Astronomical Observatory and Macquarie University).
“I made the video by combining about 3,800 frames, each of which I had processed individually,” said Dr López-Sánchez. “Each second in the video corresponds to 12 minutes in real time.”
Dr López-Sánchez took the images between June and September this year, at times when he was working as a duty astronomer at the Anglo-Australian Telescope, using a Canon EOS 600D camera.
He had to contend with bad weather, wind knocking the camera over, and, on one occasion, stubborn kangaroos that blocked his access to the camera. But after a few months he had the material.
Dr López-Sánchez has been a keen photographer since he was twelve but this is his first time-lapse project. He now has another project under way that will give a “behind the scenes” look at the Anglo-Australian Telescope.
Adapted from information issued by AAO / Dr Ángel López-Sánchez.
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Fly through a field of galaxies
THIS IMPRESSIVE VIDEO showcases results from a gigantic survey of galaxies known as the 6dF Galaxy Survey. The Survey mapped the nearby universe over almost half the sky, measuring the redshifts of more than 125,000 galaxies. Of those, 11,000 have been specially chosen and have had their velocities measured—their motions through space are helping astronomers to understand the mass involved in each galaxy, and how galaxies move and group together in the wider universe.
The survey gets its name, 6dF, from an innovative instrument installed on the Australian Astronomical Observatory’s UK Schmidt Telescope at Siding Spring in New South Wales. 6dF has a 6-degree-wide field of view—12 times wider than the full Moon—which is very wide for a large telescope. This wide field of view, coupled with the instrument’s ability to study 150 galaxies at a time, makes it an extremely efficient tool with which to do large astronomical survey projects.
The video was produced by Paul Bourke, and was structured so it could be projected on the full dome of a planetarium…which is why it seems to be distorted on a flat screen. Every dot and fuzzy ball you can see is an entire galaxy.
Adapted from information issued by ICRAR / Anglo-Australian Observatory / Paul Bourke (visuals and animation), and Peter Morse and Glenn Rogers (music).
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