By science reporter Gemma Conroy for the ABC
Black holes are the gluttons of the cosmos, devouring everything that veers too close - including light itself.
An artist's impression of a black hole. Photo: AFP / Science Photo Library
Now, an international team of researchers say they have discovered a supermassive black hole that gobbles up the equivalent of one Earth every second.
By looking at other luminous objects that are billions of years old, the team confirmed the newly discovered behemoth was the brightest and fastest-growing supermassive black hole of the past 9 billion years (that we know of).
Located in the bright constellation of Centaurus, this luminous cosmic beast is more than 500 times larger than the supermassive black hole at the centre of our own galaxy.
The findings, which are currently under review, were posted last week on a science website arXiv.
"People have been looking for these kinds of objects since the 1960s," said lead author Christopher Onken, an astronomer at the Australian National University.
"And somehow, this one seemed to have escaped all our previous efforts to find it."
An image released in 2013 of an artist's impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus. Photo: AFP / European Southern Observatory
A needle in a haystack
The team stumbled across the unusual object while they were hunting for close pairs of binary stars - the stars that orbit around the same centre of mass - in the Milky Way.
They were using the SkyMapper telescope at Siding Spring Observatory near Coonabarabran, between the Central West and North West Slopes regions of New South Wales.
Adrian Lucy, a PhD student at Columbia University in New York, found around 200 binary star candidates, but there was something strange among them, according to Dr Onken.
"One of them turned out to be something not at all like a binary system."
The Milky Way seen from Aotea/Great Barrier Island. Photo: Mark Russell
To take a closer look at the oddball object, the team went to the South African Astronomical Observatory's 1.9-metre telescope in Cape Town.
Here, they were able to look at the various wavelengths of light coming from the object, which they called SMSS J114447.77-430859.3, or J1144 for short.
"You really see the detailed fingerprints of what's making up these objects," Dr Onken said.
And it didn't look anything like a giant star.
Instead, the object had bright lines that suggested gas was moving very fast, indicating it was powered by a supermassive black hole.
Supermassive black holes - which have a mass of millions or billions of Suns - are the engines that drive some of the brightest objects in the sky: quasars.
From Earth, these luminous objects look a bit like stars, but their light actually comes from the ring of gas, dust and stars swirling around the black hole, known as an accretion disk.
As this material gets sucked into the gaping mouth of the black hole by its intense gravitational pull, it gets super hot and emits bright light.
"The gas is kind of funnelling down into a pancake shape, and that material then heats up through friction," Dr Onken said.
A black hole in the Milky Way. Photo:
Like a ball rolling down a hill, the material moves faster as it gets closer to the black hole's event horizon - the point at which not even light can escape - giving up its potential energy.
"Eventually all that stuff falls into the black hole past the event horizon, adding to the mass of the black hole as it does so."
It was this luminous, fast-moving swirl of gas that allowed Dr Onken and his team to measure the supermassive black hole's mass - an estimated 3 billion Suns.
To put that in perspective, the supermassive black hole at the centre of our galaxy, Sagittarius A*, has a mass of around 4 million Suns.
And while J1144 was fainter than other quasars identified over the past 60 years, it was much further away and still much brighter than other objects of a similar age.
"That was very exciting because these are pretty unusual finds," Dr Onken said.
Shine bright like a black hole
The team also compared J1144's luminosity over the past 45 years by looking at how it appeared in previous datasets.
They found the behemoth quasar had remained consistently bright over time, indicating that its black hole was constantly chewing on gas and anything else that came its way.
Michael Cowley, an astrophysicist at the Queensland University of Technology, said the size of the supermassive black hole probably meant it was associated with a hefty galaxy.
"Usually you'll find that the more massive the black hole, the more massive the galaxy is as well," said Dr Cowley, who was not involved in the study.
This quasar's light shines around 7000 times brighter than all of the light in the Milky Way, which means people can glimpse it from their backyard with the right telescope.
Dr Onken said people would need a telescope that's 30-40cm in diameter and a camera that can take long exposures.
J1144 is located just north-west of the Southern Cross in the sky, glowing from the Centaurus constellation.
"It's just right overhead at sunset at this time of year," Dr Onken said.
A handy galactic tool
Dr Cowley said the rare find could offer tantalising clues about the formation and evolution of galaxies.
"This is because the various properties of the supermassive black hole and its host galaxy are correlated.
"By studying black holes, we can understand the galaxy and vice versa."
While J1144 is located outside the Milky Way, Dr Cowley said its relatively close proximity to it could make it a handy tool for understanding how gas moves in and out of our own galaxy.
"If you picture the Milky Way as a spiral disc galaxy that's relatively flat, the location they spotted this thing in is fairly close to the disc of the galaxy," Dr Cowley said.
Dr Onken and his team also want to get to the bottom of what gave rise to the monstrous J1144 in the first place, along with finding out what else has been hiding in plain sight.
"We don't know if this object is a late bloomer, or if it's had some major galaxy collision that's suddenly been able to throw all this gas towards the black hole to feed it," he said.
"This has really sparked a new round of research to see what other objects have been missed by all the surveys over the years."
- ABC
