Scientists will try to directly image Sagittarius A*, the black hole at the center of the Milky Way

Black holes have historically been extremely difficult to image. They do all sorts of uncooperative things with the light around them. To date, we haven’t yet directly imaged a black hole. We can do better, but we need better resolution than we’ve yet achieved if we want to see anything other than an unhelpful smudge. To solve this problem, eight observatories have joined forces to form the Event Horizon Telescope. (Clearly ALMA, being the coolest, would be Optimus Prime.) Together, they add up to one implausibly huge telescope, and scientists want to use it to look at Sagittarius A*: the supermassive black hole at the center of our galaxy.

Thanks to a technique called very long baseline interferometry, it’s possible to gang together multiple different telescopes at multiple different sites all over the world, to emulate a telescope of equivalent size to the maximum separation between any two telescopes. The EHT makes the VLT look puny. In this case, because the EHT telescopes are so far-flung, their effective size is the size of the whole Earth. Consequently, these eight observatories are together capable of directly imaging the event horizon of the supermassive black hole at the center of the Milky Way. Some nights next April, they’re all going to simultaneously point at the center of the galaxy, to see if they can directly image Sagittarius A*.

The collaboration is called the Event Horizon Telescope because that’s exactly what the scientists intend to make of it. The array will be “sharp enough to see a DVD on the moon,” according to Scientific American. That’s fine enough resolution to detect the “shadow” we believe Sagittarius A* casts, sort of like a shadow puppet against the bright emissions coming from near the event horizon.

The Milky Way, behind the ALMA telescopes

The Milky Way, behind the ALMA telescopes. Image: ESO

The EHT will combine many of the world’s most advanced radio telescopes, including the Greenland Telescope, the Atacama Large Millimeter Array (ALMA), and the South Pole Telescope (SPT).

It’s not all skittles and beer yet. Sometime before next April, the Large Millimeter Telescope is going to have to have a new receiver installed, because right now it’s not even capable of observing on the same 1.3mm wavelength as the other telescopes. In December, the South Pole Telescope is having a new high-frequency receiver installed, too.

If this all sounds a bit like it’s flying by the seat of its collective pants, that’s my impression too. The EHT collaboration wasn’t even a done deal until they finally got telescope time on ALMA, which increases the sensitivity of the Event Horizon Telescope by tenfold.

Once the observations are all said and done, and the data has been collected, it will be some months before it’s all processed. We’ll be over here trying very hard to be patient.

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