"One of the really nice things about this is taking an image of black hole event horizon has been beyond our reach for so long that it's been a pleasant surprise to build upon these existing technologies and capture an image so soon," says Monash University astrophysicist Professor Michael Brown. "It really complements the exciting gravitational wave discoveries of merging black holes and the creation of new black holes."
The project to capture Sagittarius A began in April this year.
Radio telescopes all over the world were synchronised and pointed towards the centre of the Milky Way. Combined, they produced an Earth-sized telescope capable of incredible resolution over immense distances.
All the data from each of these radio telescopes have now been gathered. It's being processed to filter out background noise and interference. What's hoped to be left behind is something looking like this.
SIGHTING SAGITTARIUS A
At the heart of every galaxy is a supermassive black hole. It's all part of the cycle of life and death on an interstellar scale.
This one is 26,000 light years away. Swirling around it are the billions of stars of our galaxy. At its core is a singularity millions of times heavier than that of the Sun.
This is what gives it such immense gravity that not even light can escape.
Supermassive black holes are unpredictable beasts. They can lie dormant for centuries before suddenly flaring up as a quasar, driving powerful jets of superheated subatomic particles into intergalactic space.
It will do this as it devours a nearby star, or pulls in one of the dense clouds of gas and dust swirling around it. These same clouds are blocking Sagittarius A from the view of optical telescopes. But some radio waves can pass through such obstacles unhindered.
And Sagittarius A has been somewhat flatulent of late.
"Astronomers hope to capture our Galaxy's central black hole in the process of actively feeding to better understand how black holes affect the evolution of our Universe and how they shape the development of stars and galaxies," a statement from the National Radio Astronomy Observatory reads.
Which is why the world has combined its radio telescopes in an effort to peer into the darkness.
"High resolution imaging of the event horizon also could improve our understanding of how the highly ordered Universe as described by Einstein meshes with the messy and chaotic cosmos of quantum mechanics — two systems for describing the physical world that are woefully incompatible on the smallest of scales," NRAO says.
EVENT HORIZON TELESCOPE
Photographing a black hole is no point-and-click exercise.
It may be four million times heavier than our Sun. But it's 26,000 light years away. Perfectly black. And surrounded by stuff.
This is why the millimetric scale of modern radio telescopes is crucial.
"For decades radio interferometry has been done at centimetre wavelengths using telescopes spread across continents," says Professor Brown. "However, if you do the same observations at millimetre wavelengths then you can produce images with better resolution, and see (in silhouette) the black hole at the centre of our galaxy.
"The catch is interferometry at millimetre wavelengths is far more challenging than interferometry at centimetre wavelengths."
"One nice thing about millimetre wavelengths is, compared to visible light, it is not greatly impacted by the interstellar dust between us and the centre of the galaxy," Professor Brown says. "Basically the wavelength of the light is so much bigger than the dust particles that it travels past them."
To get the best possible picture, radio telescopes thousands of kilometres apart are being pointed together towards Sagittarius A to capture what they can simultaneously.
Together, their resolution has been described as being the equivalent of being able to read the date on a coin in Brisbane with a telescope in Perth.
This data will be refined, compared, and fed into software specifically designed to identify the supermassive black hole.
What they're hoping to see is radiation — and the immense black disk of Sagittarius A in outline against it.
"In the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) projects, which are both aiming to capture the shadow of a black hole's event horizon for the first time, researchers began to develop effective image analysis methods using simulation data well before the start of the observations," NRAO says.
The data was collected in April, and has been undergoing processing in the United States and Germany. The last component — observations from the South Pole Telescope — has only just been delivered after the weather cleared enough to allow flights out.
"Then data calibration and data synthesis will begin in order to produce an image, if possible," The NRAO says. "This process might take several months to achieve the goal of obtaining the first image of a black hole.
