A visualisation of data captured showing clumps of gas swirling around at about 30% of the speed of light on a circular orbit just outside a four million solar mass black hole. Picture: ESO
A visualisation of data captured showing clumps of gas swirling around at about 30% of the speed of light on a circular orbit just outside a four million solar mass black hole. Picture: ESO

Staring into a black hole’s abyss

THERE's a monster at the heart of our galaxy. And, for the first time, we've seen it feeding.

We know black holes exist. It's just that we've not actually seen them.

They're black. They're so strong not even light can escape.

So, the best science can hope for is capturing the 'shadow' of a beast such as Sagittarius-A, the supermassive black hole at the heart of our galaxy, as it draws in matter around it.

That's now happened.

Telescopes, finely tuned to peer through the gas clouds between us and the galaxy's core, have spotted something 'wobbling' around in a tight circle. It's moving so fast, and in such a tight orbit, that it's right on the edge of the laws of physics.

That means whatever this bright blob is wobbling around breaks those laws.

That means a black hole.

It's swirling at 323 million kmh at the brink of where space and time lose meaning. By watching it, astronomers hope to learn what's really going on at that crossover point.

But it's already given us our best look at what a black hole actually 'looks' like.

"Astronomers probably think the existence of the blackhole itself is old news," Monash University astrophysicist Michael Brown says. "The fun bit is how close we are getting to the event horizon."

But the best may be yet to come.

"New results from the Event Horizon Telescope should be on the horizon - that should look even closer. We are really looking in towards the abyss here.

SAGGITARIUS A

Like almost all galaxies, we know there is a supermassive black hole at the heart of the Milky Way. It's gravity is the equivalent of some four million Suns.

It's a long way off. Some 25,000 light years away.

But it's bright. Interstellar gas speeds up as it approaches it. As the gas particles jostle one another, this creates friction - and a glow - as it swirls into an accretion disk.

The challenge is peering through this immense cloud to see the actual point of no return. The event horizon.

Over 15 years of observations, astronomers have noticed a particular point in this gas cloud flicker brightly. Sometimes, it flares up some 30 times brighter than normal - but just for 5 minutes or so.

The Max Planck Institute for Extraterrestrial Physics in Garching, Germany, has been tracking these flashes. They've managed to do so with incredible accuracy.

It's moving clockwise. It's moving at roughly a third the speed of light. And, over the course of three months, it traced out the form of a tiny circle.

So what could possibly producing such flashes?

Astronomers propose they could be 'hot spots', blobs of magnetically heated plasma stretched to breaking point in the last possible position for a secure orbit. Beyond this point, everything starts to irrevocably tumble down to the event horizon itself.

Beyond the event horizon, reality itself vanishes.

"We are looking at stuff at about 7.5 times that of the black hole - event horizon distance," says Brown. "In other words, if the event horizon has a radius of 6 million km, we are looking at stuff just 45 million kilometres from the black hole. Sounds like a lot but for comparison the Sun is only 150 million kilometres from Earth. This is so spectacularly close that stuff is moving at a third of the speed of light!"

It's not the superheated plasma itself that generates the flashes.

It's the gravitational lensing of the black hole itself - twisting space-time to focus some of the energy emitted by the plasma back out into space like a searchlight.

 

 

SNARED BY GRAVITY

Things get weird around black holes. That's why astronomers are so keen to look at it.

They hope their observations will shine some light on the theories of the likes of Albert Einstein and Stephen Hawking.

Everything about black holes are infinite. And infinity just doesn't add up.

So, a set of telescopes in Chile have been feeding a new tool called GRAVITY everything they see from the heart of the galaxy.

Part of the Very Large Telescope array run by the European Southern Observatory, the four 9m telescopes combine their recordings in real-time, assembling the virtual equivalent of a telescope some 70m in diameter.

Flares have been seen coming out of Sagittarius A before.

But, at this new resolution, they've been able to track the flashes of charged plasma at the point where - if it goes any faster - its own gravity increases to a point where it irrevocably pulls it into the black hole.

This "provides long-awaited confirmation that the object in the centre of our galaxy is, as has long been assumed, a supermassive black hole," an ESO press release reads.

The Max Planck Institute for Extraterrestrial Physics study leader Reinhard Genze said: "This always was one of our dream projects but we did not dare to hope that it would become possible so soon."


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