Galactic Naval Gazing

More news from outer space this week where there is a race afoot in the world of astrophysics, a race to achieve what, just a decade or two ago, would have been assumed was simply not possible. Several teams around the world are doing their very best to visualise a blackhole.

Now, by their very definition, blackholes are very hard to see. They don’t give off any light at all, nor heat. It could be possible that they give off a form of energy known as Hawking radiation, as proposed by Stephen Hawking in the mid 1970s, but this is still theoretical. How, then, could it be possible to ‘see’ one? The solution is to look not at the black hole itself, but at the matter right next to its event horizon, the boundary at which nothing can escape the immense pull of the black hole.

One such effort, published just last week in The Astrophysical Journal, used the Very Long Base Array telescope. The VLBA is a series of ten very large radio telescopes that spans the continental US along with some extra ones in Hawaii, the Caribbean and one in Europe. The size of this array allows exceptionally fine details to be resolved even hundreds of millions of light years away.

In this case, two black holes 750 million light years away were seen to be orbiting each other. The team, from the National Radio Astronomy Observatory in the US, used multiple observations of the galaxy 0402+379 over a 30 year period to realise that there were actually two black holes present where it had been thought there was just one. This is the first time two black holes have been resolved at a galactic core like this.

Using improved methods over the course of the observations, the team could determine that the combined mass of the two black holes is 15 billion times that of our sun and that they take about 30,000 years to revolve around each other once; though these figures could be refined with further observations.

Attempting to see a black hole much closer to home is the Event Horizon Telescope. This is an array of sub-millimetre radio telescopes that truly does span the whole globe. From Greenland in the north to Antarctica in the south, and all across Europe and the US, this network of telescopes will create a virtual scope on a planetary scale.

Supermassive black hole with torn-apart star (artist’s impress
The architecture of a supermassive black hole. Credit: ESO, ESA/Hubble, M. Kornmesser/N. Bartmann

Not all the planned telescopes for the EHT are yet up and running but the team nevertheless tried their luck and conducted a week of observations back in April of this year. Unfortunately, it will still be some months before we know what the array saw; partly because the technique used, Very Long Baseline Interferometry, takes a Very Long Time To Process, and partly because the data recorded by the telescope down at the south pole is stuck there until September when it will become possible to fly the hard disks out as winter comes to an end. It will be some time next year before we find out the results of this trial run.

The goal is to observe the supermassive blackhole at the centre of our own galaxy, Sagittarius A*. Of course, what we will actually be seeing is how the matter and light right next to the event horizon behaves, which is as good as we’re ever likely to get. This, though, would provide enormous insights into black hole mechanics and allow us to begin confirming or denying our theories on how these most mysterious of objects work.

Last year we heard what it sounds like as two massive black hole collide into each other with the discovery of gravitational waves; could next year be the year we actually see what one looks like?


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