Image Credit: EHT Collaboration
55 MILLION LIGHT years from Earth, what was previously believed to be ‘invisible’, has now been pictured. The iconic picture that has been plastered over the internet this past week shows the accretion disc around a black hole:orbiting around the black hole diffuse material produces this image with immense temperatures causing these particles to emit electromagnetic radiation. The black mass in the middle of the photo marks the ‘event horizon’ - a gravitational boundary beyond which neither light nor matter can escape.
But why the halo shape? To put it simply, whatever angle the black hole is viewed from, a halo shape will form due to gravity bending the light. Captured by a large global network of radio telescopes, called the Event Horizon telescope, the first picture of the supermassive black hole was produced in order to test Einstein’s general theory of relativity which scientists use to explain phenomenon in our galaxy.
The scientific paper published alongside the incredible image said: “Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. Many of the features of the observed image match our theoretical understanding surprisingly well.” It took a huge collaborative effort to pull this off - the eight telescopes were located in Hawaii,Mexico, Arizona, Sierra Nevada,Chilean desert, and Antarctica. In order to coordinate the exact timings required to take the photo, anatomic clock called the hydrogen maser was used, giving the time accurately within one second every 100 million years.
Among the hundreds of people working on this project, a notable mention must go to Katie Bouman, who when studying atMIT came up with the algorithm that made the black hole image a reality. In her own words, the blackhole is so far away it is the equivalent of attempting to view an orange on the surface of the moon from earth. In order to see this far into space an optical telescope roughly equivalent to the size of the earth was needed - an impossible feat.
Instead, Katie’s computer algorithm made it possible to reconstruct the black hole image by having the eight distinct view points which contributed to produce new information as the earth rotated.Using ‘puzzle pieces’ from a variety of different images of space and everyday objects alongside information from the telescope, the algorithm combined data from many different sources in order to put together the most likely representation of the black hole. The idea is, no matter what puzzle pieces are used, if the images produced are comparable with each other, this will be a true representation of the mysterious supermassive black hole.
Two years ago, speaking at theTEDx conference in 2017, when the Event Horizon Telescope Collaboration was in full swing, this project’s success can be attributed to the “melting pot of astronomers,physicists, mathematicians and engineers, and that’s what it took to achieve something once thought impossible”.