Seeing the Unseeable
There is something to be said for being able to see the theoretical. Often, our models can predict things that we will never be able to prove—never able to see with our own eyes. On April 10, 2019, the Event Horizon Team revealed the first picture of a black hole. “We have seen what we thought was unseeable. We have seen and taken a picture of a black hole,” said Harvard’s Sheperd Doeleman, the leader of the project.
Photos were taken of two black holes: M87, a massive black hole found at the center of the Messier 87 galaxy, and Sagittarius A-star (SgrA*), a black hole found at the center of the Milky Way. Although M87 is much farther away than SgrA*, it is much more active and massive, enabling scientists to capture a significantly clearer picture of it. The picture of SgrA* has yet to be released. These black holes take up an unimaginably small amount of our sky at 40 microarcseconds for M87 and 50 microarcseconds for SgrA*. This is the equivalent of 1 to 2 hundred millionths of a degree on our horizon.
Our current photos reveal the innermost part of M87’s accretion disk and the ‘shadow’ cast on its center from the black hole. M87 itself has a mass of over six billion times that of our sun and its event horizon, the point at which even light can no longer escape its gravity, is the size of our entire solar system. The team used radio waves to make the image so we could see past the interstellar dust and outer accretion disk. One side of the ring is brighter than the other. This is because the plasma of the accretion disk is moving towards us in that section, and it appears brighter because of a property called relativistic beaming.
These photos were the culmination of years of work by over 200 scientists from 60 institutes in 18 countries, costing between fifty to sixty million dollars. "It really brings home how fortunate we are as a species at this particular time, with the capacity of the human mind to comprehend the universe, to have built all the science and technology to make it happen," said astrophysicist Priyamvada Natarajan of Yale University.
When initial estimations were taken, it was thought that a single telescope would have to be the size of the Earth to be able to snap a picture of these two giants. In a TED talk recorded before the pictures were taken, Katie Bouman, one of EHT’s head software engineers, compared this to “trying to take a picture of an orange on the face of the moon.” A more feasible and creative solution was found, however. The Event Horizon Team used a network of eight of the most high-tech telescopes scattered around the globe to each take scattered fragments of a picture, then a computer algorithm was used to attempt to fill in the missing pieces. The effect was over a petabyte of information conglomerated into two breathtaking photos.
These pictures have an enormous impact on modern physics. Firstly, it proves once and for all that black holes exist, which bolsters our confidence that the current models of the universe are accurate. It affirms the initial work of Albert Einstein and Schwarzschild, who affirmed his theory and furthered the existence and shape of black holes. This news came after scientists first detected signals of black holes interacting on September 14, 2015, when LIGO picked up gravitational waves. Many scientists considered a picture to be the logical next step.
Pictures of black holes also serve as amazing tools. From these pictures, it becomes possible to measure their size, mass, activity and, particularly in the case of SgrA*, how it affects the galaxy we live in with greater accuracy than ever thought possible. We’re going to need this too. We know that smaller black holes come from collapsed stars, but we do not know how supermassive black holes like M87 and SgrA* are formed.
Black holes have been used as tropes in science fiction for decades. Sometimes, it’s hard to remember that we’d never actually seen one before. Finally, to quote University of Waterloo theoretical physicist Avery Broderick, “Science fiction has become science fact.” Thanks to an international team of over 200 scientists and telescopes everywhere from Hawaii to the South pole, we finally can see the unseeable.