Fossil remains of a black hole's past feeding frenzy have been discovered deep within one of the largest galaxy clusters in our sky.
Astronomers also spotted a plasma shock wave that defies physics, and a halo of radio energy within the same galaxy cluster.
The cluster — Abell 3266 — lies 800 million light-years away and stretches across 300 million light-years of sky in the southern constellation of Reticulum.
An international team of astronomers, led by Christopher Riseley of the University of Bologna in Italy, studied the cluster in detail using the powerful Australian Square Kilometre Array Pathfinder radio telescope in outback Western Australia, and the smaller Australia Telescope Compact Array in Narrabri, New South Wales.
The team report their findings today in the Monthly Notices of the Royal Astronomical Society.
Galaxy clusters are some of the biggest and most dynamic objects in the universe, said astrophysicist and co-author Tessa Vernstrom of the University of Western Australia.
"It's where you've got the interplay of dark matter and galaxies and a lot of different physics going on," Dr Vernstrom said.
"You've got galaxies merging, active galaxies with big black holes [blasting jets of energy into space], shockwaves and turbulence."
Abell 3266 has all that — and a lot more that has scientists puzzled.
The team combined their findings from the radio telescope (coloured red, orange and yellow), with images taken in X-ray and visible light (blue and white) to produce the stunning image above.
So let's dive in and take a closer look at the cluster.
Active galaxies
The cluster has a number of active galaxies, with supermassive black holes at their heart sending out massive jets of energy.
One galaxy in the bottom right-hand corner stands out. Instead of having big jets shooting out from its centre, they are bent around.
The curved jets are caused by the movement of the galaxy in the cluster.
"So it's kind of like a pressure wind that pushes the jets back," Dr Vernstrom said.
"It can tell you about the dynamics going on and how everything is moving around each other."
Fossil of a feast
Not all galaxies are active. At the top right of the image are the fossil remains (red) of a supermassive black hole that has stopped feeding on its galaxy (the small white blob towards the bottom of the red area in the inset image).
"Sometimes the jets [coming out of supermassive black holes] just switch off," Dr Vernstrom said.
"And so as the black holes are not being fed new material, the stuff they've already put out just kind of ages and starts to fade away."
Relic shockwave
At the bottom left-hand corner is what appears to be a remnant of a shockwave created when some parts of the cluster passed through each other.
But instead of facing inwards, the relic, dubbed "wrong way", is facing away from the centre of the cluster.
"If it's a shock wave, you might think it would bend down like an arc around the edge, but this one is flipped around," Dr Vernstrom said.
Sometimes it can be hard to tell if the effect is real or a product of the way it has been imaged, but Dr Vernstrom said the team thinks it is real.
The relic is also a lot brighter in the radio spectrum than expected in any models.
"So we don't really understand what that's telling us," she said.
"Maybe there's some kind of new physics going on there that we haven't fully understood when our models can't match the observations."
Central halo
Lying at the centre of the cluster is a faint blob of radio emissions known as a halo.
"We actually can't even really see it because it's basically so faint and spread over this large area," Dr Vernstrom said.
The zoomed-in image below shows the boundaries of the halo within a blue dotted line.
Dr Vernstrom said haloes appear in clusters where there have been recent mergers, but they are rare.
"We only know of about 100 of these objects, and we have never seen one in this cluster before," she said.
The emissions are produced by electrons that have been jiggled around by turbulence created by the interaction of galaxies, gas and particles packed into the centre of the cluster.
"It's kind of like if you had two storm fronts that collide and merge — the structures in the clouds and weather get all jumbled up."
The electrons are boosted as they travel around magnetic field lines between galaxies.
Power of new telescopes
While there are thousands of clusters, Dr Vernstrom said we've found "surprisingly few" objects like those in Abell 3266.
"They are basically just hard to detect."
She said it was only possible to see this cluster in this much detail using new telescopes.
"We would never have seen this [without] ASKAP."
The telescope uses a series of 36 antennas to detect sources of radio emissions — the longest wavelength of energy — in the sky.
"By looking in the radio, you see kind of different physics than when you look in the other wavelengths," Dr Vernstrom said.
Using several antennas spread across 6 kilometres, it is also much more sensitive and can see more detail than smaller radio telescopes.
Dr Vernstrom said the discoveries in this cluster were just the beginning of what scientists would find with ASKAP.
Over the next five years, the telescope will survey the entire southern sky.
"We're going to see a lot more of this kind of stuff."
