April 10, 2019 has marked a historic point in the timeline of astrophysics – the moment when we first see a Black Hole. The behemoth black hole Messier 87 (M87) is located about 55 million light-years away from Earth in the Virgo constellation. Shaped like an asymmetrical doughnut, this fuzzy image shows that black holes obey Einstein’s 100 year old Theory of Relativity. Building upon Newton’s law of universal gravitation that every mass attracts every other mass in the world, Einstein showed that matter and space-time mutually interact. The general theory of relativity implies the continuous expansion of the universe, the existence of black holes and gravitational waves. If gravity curves space then a massive object could deflect a light beam. One such extraordinary mammoth body of mass is the black hole. Black holes have an enormous mass compressed in a tiny space and have such an intense gravitational force that no matter or radiation, not even light, can escape from inside it. Once anything enters a black hole – it’s gone forever. The boundary of the black hole is called the event horizon.
The success of capturing this image came after years of research and planning and involved more than 200 scientists and strong international cooperation. To observe such a giant black hole millions of light-years away, scientists required a telescope the size of Earth. This was made possible with the use of the Event Horizon Telescope (EHT). This virtual telescope links eight ground based radio telescopes stationed on five continents. On four separate days in one week of April 2017, the ETH observed the area around M87 and collected about 350 terabytes of data per day. Using the concept of event horizon, the scientists that accomplished this feat scanned their data for the bending of light by gravity, a phenomenon known as gravitational lensing. The process from the unabridged data to the one image we see today took almost two years.
This revolutionary discovery was published in a series of six papers in The Astrophysical Journal Letters. “We have taken the first picture of a black hole,” said EHT project director Sheperd S. Doeleman of the Harvard-Smithsonian Center for Astrophysics research institute. “This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.”
The EHT shows that the mass of M87 is 6.5 billion solar masses (sun’s mass) and this black hole has a diameter of about 38 billion kilometers – that is, it is larger than the size of our entire solar system. Also to note, this black hole spins clockwise. The shadow of the black hole is the only current way of forming the image of M87. The image is a ring of light with a dark shadow in the middle.
The next black hole to be captured in a jpeg. will, hopefully and soon, be our very own Sagittarius A* – the massive black hole sitting in the middle of our Milky Way galaxy. Though Sgr A* was a strong contender for being the first black hole to be photographed, the sheer size of M87, about 1,000 times the size of Sgr A*, made M87 a more possible capture. The possibilities are endless and the Event Horizon Telescope may soon see hundreds of black holes.
Vedangana Raj