The Messier 87 black hole: Humanity's first look at the powerful celestial object
By: Dipasha Dayani
The black hole at the center of the Messier 87 galaxy, 54 million light years away from Earth. Event Horizon Telescope Collaboration.
Black holes were discovered in 1915, Cygnus-X1. Since then, about 50 have been confirmed or are at least suspected to exist, with some scientists believing that millions exist in the Milky Way as a whole. When you google the word “black hole”, various interpretations show up - however, actually capturing a real photo requires a lot of effort and resources, hence why it was never done. That is, until April 10th, 2019, when the first -albeit blurry - picture of a blackhole was released. Coming up on the 6-year anniversary of the date, let's explore how this great feat was accomplished.
What are Black holes and how do we know one exists (simplified)?
To put it simply, a stellar-mass black hole is an area where the force of gravity is extremely strong, to the point where light can’t escape. They are the result of a large star dying (once it has burned through its fuel), collapsing on itself, with a large amount of matter being extremely densely packed. Since light cannot escape, black holes are not visible to the naked eye. To detect one, scientists usually study the effects of its gravity on the objects around it, oftentimes looking at their motion to find potential black holes. Should a star and a black hole orbit close to one another, light is created, which can be detected. Additionally, should the black hole be particularly strong, it can pull gases off the closest star and create what is called an accretion disk, with the gases surrounding the black hole being heated and releasing x-rays and light. These X-rays can then be detected and used to locate black holes. Supermassive black holes have about one million-one billion (yes, that large of a range!) more mass than stellar mass ones. Although how they are created isn’t fully known yet, it's hypothesized that they are created with the collapse of supermassive stars, and then feed off neutron stars and other spatial-objects around them.
The journey to capture a view of a black hole
Due to the nature of light within black holes, photographing one (or even having physical evidence of one) has been an impossible task. The supermassive black hole that was initially photographed was located at the centre of the Messier 87. It was photographed due to the EHT (Event Horizon Telescope) Collaboration, a network of various telescopes spanning North and South America and Europe. By pointing these telescopes across the planet, an almost earth-sized view of the black hole could be formed. This system created over 5,000 trillion bytes of data over a 2 week span. When fed into supercomputers, a series of images were created, showing the glowing accreditation disk.
In 2022, a new image was released from this project, this time of Sagittarius A, the black hole at the centre of the Milky Way. Though they look similar, the M87 is much larger, more than 1000x compared to Sagittarius A. This also contributed to the difficulty of taking a picture of it, because while gas orbiting M87 took a couple days or weeks, it could take approximately 10 minutes with the latter black hole. That is why, unlike the first image released (where most products created by the data looked similar), Sagittarius As’ images wildly differed, with the final product being an average of all created. About 80 institutions (a total of over 300+ researchers) worked for 5 years to capture and combine data.
M87 supermassive black hole vs. Sagittarius A. Event Horizon Telescope Collaboration.