At the center of our galaxy, lies a region known as Sagittarius A* -- widely believed
to be the location of a supermassive black hole, about 4 million times the mass of our
sun.
But while there is insurmountable evidence that this black hole actually exists, there
is some skepticism surrounding it.
That’s because like all black holes, astronomers have yet to observe it directly to confirm
it’s existence.
But the race is on to be the first.
This the Cerro Paranal in the Atacama Desert in Northern Chile.
At around 2600 metres above sea level, the desert sits above much of the moisture in
Earth’s atmosphere, making it one the driest places on earth, an ideal place for building
the world’s most powerful telescope.
But observing a supermassive black hole in the middle of the Milky Way takes more than
just one powerful telescope in near perfect conditions, it takes several.
The ‘Very Large Telescope’ array or VLT for short, sits in the Atacama Desert and
uses four massive optical telescopes to study the goings on in Sagittarius A Star.
[Oliver] We are roughly thirty thousand light years away from the centre of our galaxy in
a spiral arm, but we can very well study this region of the galactic centre.
Astronomers are able to utilize the power of all four telescopes in the VLT array to
explore and understand the Milky Way using a technique called interferometry.
Normally, the resolution of an optical telescope is limited by the size of the main mirror
inside it.
The bigger the mirror, the more light can be picked up, the more detail you can see.
But, if we wanted to see the depths of the Milky Way with just one telescope, we would
have to build a 100 meter wide mirror.
Which would be technically impossible.
But with interferometry, the light beams captured by all four optical telescopes in the VLT
array, can be combined using a computer.
This basically creates a single telescope with a “virtual mirror” as large as the
furthest dishes are apart from each other.
This takes care of the impossible to build, gigantic mirror.
[OLIVER] We are using a very fundamental property of light.
In this case we can recreate almost the resolution of a hundred meter diameter telescope.
This means astronomers like Oliver can use the VLT to study the center of our galaxy,
including activity surrounding the supermassive black hole.
[OLIVER] ….We know that this black hole is actually not black.
Once in awhile it flares, so we see it brightening and darkening.
We believe there must be some matter that is falling in.
[OLIVER] If we can study these motions which happen so close to the black hole, we have
a direct probe of the space time close to the black hole.
In this way we have a direct test of general relativity in one of the most extreme environments
which you can find in the universe.
The extreme environments within Black holes are down to the strong gravitational forces
they possess meaning that nothing - including light—can escape its clutches.
Currently Oliver’s work is looking at relativity around the black hole thought he hopes to
one day use the VLT to see exactly what happens to space time directly inside it.
But as much as it seems like the VLT is sitting alone in this vast, dry desert, they actually
have a neighbor.
(insert distance between 2)
This is the Atacama Large Millimeter Array also known as ALMA.
It is a radio telescope comprised of 66 state-of-the-art antennas, equipped with receivers so sensitive,
they can pick out a golf ball 9 miles away.
And by using interferometry to harness all 66 antenna’s ALMA is able to study regions
of space that the optical VLT cannot -- notably the coldest and dimmest objects in our universe,
like the center of a supermassive black hole or where stars are formed.
[GIANNI] In the universe, the stars are forming in the cold matter...
….In the optical it is much more difficult to do interferometry...
...you cannot investigate, for example, cold matter because you cannot see it.
….ALMA can go behind this limitation and can see where the stars are formed.
In this respect, ALMA is opening, to me, a completely new horizon.
You can see details that are better than what space telescopes can observe in space out
of the atmosphere.
But what’s really exciting for astronomers like Gianni, is that ALMA is actually a smaller
piece of a much, much larger puzzle.
In 2015, the array became part of The Event Horizon Telescope, a project that utilizes
interferometry to unite a network of radio telescopes from around the world.
Essentially the EHT is a virtual radio telescope the size of our planet, making it the largest
ground-based astronomical project in existence.
By 2017, the EHT hopes to observe the ‘event horizon’ of the supermassive black hole
at Sagittarius A* -- which is the boundary marking the limits of the black hole beyond
which nothing can escape.
Which has never been done before and could provide further evidence that this black hole
at the center of our universe, exists.
But this isn’t about who can do this first.
For these astronomers working in the Atacama, it is about having a greater understanding
of the universe.
It’s about working together, pooling knowledge to do something that has never been done before.
Simply put...
[OLIVER] Our main science goal is, in fact, to observe the black hole in the galactic
centre.
The DNews team recently travelled to the Lowell Observatory in Arizona to find out what ground
telescopes can tell us about the universe.
Click here to watch that episode now.
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