Black Hole SAGITTARIUS A*

First-Ever Image Of Supermassive Black Hole At Centre Of Our Galaxy

    May 12 turned out to be a historic day as the world’s first image of the chaotic supermassive black hole at the center of our own Milky Way galaxy doesn’t portray a voracious cosmic destroyer but what astronomers called a “gentle giant” on a near starvation diet. The photograph is a result of observations by over 300 scientists and a network of eight major observatories around the world. 

    The scale of this discovery is further only seconded by the collaborative effort that went into it. A global research team called the Event Horizon Telescope (EHT) Collaboration produced the image using observations from a worldwide network of radio telescopes, spanning over five years of problem-solving. The EHT is the combined ingenuity of over 800 researchers over five continents and 13 stakeholder institutes. They developed a powerful virtual telescope that joined eight existing radio observatories worldwide into a single "Earth-sized" virtual telescope. The EHT monitored Sgr A on several nights in 2017, capturing data for several hours at a time, akin to a camera with a very long exposure period. 

    Astronomers have named the Milky Way's supermassive black hole Sagittarius A* — abbreviated to Sgr A* and pronounced sadge-ay-star — because of its location in the Sagittarius constellation. The European Southern Observatory (ESO), one of the contributors to imaging the black hole, shared a video wherein the astronomers zoom into the Sgr A* constellation. Notably, the image does not show the black hole itself, since these objects do not allow light to escape away from them. Rather, it depicts a dark central region, called a shadow, surrounded by a bright ring-like structure that actually are glowing gases around the black hole. The picture also shows light being bent around the black hole due to an overwhelmingly strong gravitation pull. 

    The black hole was named in the 1980s due to its proximity to the Sagittarius constellation in the sky, and initial estimates calculated it to be a mammoth 26 million kilometres in diameter. It sits on its throne at 26,000 light-years away from our solar system, having a mass 4.3 million times that of the sun. This development is monumental as it provides precious data that will help us understand better the intricate mechanisms of the ever-elusive black holes phenomena. The image, which undeniably looks like a warm doughnut (let’s face it!), provides valuable and overwhelming proof that the object at the centre of our galaxy is, in fact, a Supermassive Black Hole (SMBL).

    In the 1980s, two teams of astronomers started tracking the motions of stars near this mysterious source of radio waves. They saw stars whirling around a dark object at speeds up to a third of the speed of light. Their motions suggested that at the center of the Milky Way was a black hole 4 million times the mass of the Sun. Reinhard Genzel and Andrea Ghez later shared the Nobel Prize in Physics for this discovery. The size of a black hole is defined by its event horizon – a distance from the center of the black hole within which nothing can escape. Scientists had previously been able to calculate its distance.

     The new image of Sgr A* follows the first-ever image of a black hole, which was obtained by the EHT in 2019. That ground-breaking image was of M87*, the supermassive black hole at the center of Messier 87, a galaxy located 53 million light years from Earth. M87* is a goliath compared to Sgr A*, with a mass of 6.5 billion suns (more than 1,000 times heavier than our own black hole), and a size that could easily swallow the entire solar system. And yet the image of M87* reveals a bright ring structure, much like Sgr A*. The similarity between the two images confirms another prediction of general relativity: that all black holes are alike, no matter their size.

    The researchers' efforts are sure to redouble after the endeavor's success, and they're now planning on doing something even more extraordinary: rather than a single still image, the next step is to film the black hole throughout a period of time, capturing the dance of the simultaneously wave and particle-like photons to showcase the black hole's dynamics. One can only wonder how many millions of CPU hours that effort will take.