The object depicted below may look like a flaming nightmare doughnut and the picture itself may seem fuzzy and indistinct, but the image is actually one of the sharpest ever made and the object is profoundly important both for the astronomical community and for life on earth in general.
The object is Sagittarius A* (pronounced, somewhat annoyingly, as “Sagittarius A-star”), the supermassive black hole at the heart of our Milky Way galaxy. The image is the result of a five-year multinational effort to link eight radio observatories into a single, planet-size telescope staring in the radio, x-ray, and microwave bands of the electromagnetic spectrum. Only radio telescopes can peer through the dust lanes, gas clouds, and teeming stellar metropolis of our galaxy’s central bulge. The image was released by the 300-person Event Horizon Telescope team on May 12.
But let’s back up. Sagittarius A* (SgrA*) lies at a distance of about 27,000 light years from earth, at the hub of the Milky Way’s spiral arms. It has a mass of 4.3 million suns, and the accretion disk—that glowing orange ring—would fit inside the orbit of Mercury. At the heart of the accretion disk is the shadow of the event horizon where gravity is so powerful that even light cannot escape. And at the centre of the event horizon is the mysterious black hole singularity. More on that later.
SgrA* is very active, which is one reason why this image is so impressive (the other is that from earth SgrA* is as small as a doughnut lying on the moon). The accretion disk, a churning froth of gas, dust, and plasma circling the event horizon at a substantial fraction of the speed of light, is so dynamic that it can change dramatically on a scale of minutes. To meet this challenge, the EHT team averaged a series of images (taken in April 2017) using a global network of supercomputers. Further research will hopefully determine whether those glowing lobes are persistent structures or flashes of energy released as infalling matter was shredded by the intense gravitational field.
So, the image is important because it is a fantastic technological achievement and because it depicts, for the first time, the colossal object that our sun orbits, similar to the way earth orbits the sun. It is the anchor of our home galaxy. But for me, that’s not it.
To me, the most impressive thing is that the image isn’t really a picture of an object, a thing, at all. As far as I know, it is one of only two pictures ever taken of a thing-not-thing in an otherwise familiar universe of tables, chairs, planets, and people. It is not a thing because a black hole singularity is a region of space in which gravitational collapse has caused space to wind into ever-tighter whorls, further accelerating gravitational collapse and further causing space to contract in a never-ending cycle like a puppy chasing its tail, until the puppy shrinks smaller than a proton and becomes a mathematical point of infinite mass, infinite distance, and infinite spacetime curvature.
No one knows for certain what really happens at the singularity because we have no accepted theory to explain it and direct observation is impossible. Beyond the event horizon, time and space likely switch roles: space becomes time-like because it moves in one direction for infinity, and time becomes space-like because one could in theory move back and forth along it. The singularity, whatever it really is, has no apparent end.
That’s the really interesting thing, though. How often in life does one get a chance to gaze into a literal infinity that is also the vanishing point of human knowledge? With a little imagination, there it is for you, right in the center of that flaming fuzzy doughnut.
Stargazer by Dennis Vanderspek