Scientists on Thursday provided the first look at the monster lurking at the centre of our Milky Way galaxy, in an image of a supermassive black hole that devours any matter wandering within its enormous gravitational pull. Their image of Sagittarius A*, or SgrA*, is only the second ever taken of a black hole. The feat was accomplished by the same Event Horizon Telescope international collaboration that in 2019 unveiled the first photo of a black hole, which is at the centre of a different galaxy. Sagittarius A* has four million times the mass of our Sun and is about 26,000 light years from Earth. A light year is the distance light travels in a year, or 9.5 trillion kilometres. Black holes are extraordinarily dense objects with gravity so strong that not even light can escape, which makes finding them challenging. A black hole's event horizon is the point of no return beyond which anything — stars, planets, gas, dust and all forms of electromagnetic radiation — is dragged into oblivion. Project scientists have looked for a ring of light around a region of darkness representing the black hole. It is super-heated disrupted matter and radiation circling at tremendous speed at the edge of the event horizon, and is known as the black hole's shadow or silhouette. The Milky Way is a spiral galaxy that contains at least 100 billion stars. Viewed from above or below it resembles a spinning pinwheel, with our Sun on one of the arms and Sagittarius A* at the centre. The image released in 2019 of the supermassive black hole in a galaxy called Messier 87, or M87, showed a glowing ring of red, yellow and white surrounding a dark centre. The M87 black hole is far more distant and massive than Sagittarius A*. It is about 54 million light years from Earth and has a mass 6.5 billion times that of our Sun. The researchers said that the image of Sagittarius A*, despite it being much closer to our solar system than M87, was harder to take. The diameter of Sagittarius A* is about 17 times that of the sun, meaning it would be within the innermost planet Mercury's solar orbit. In contrast, M87's diametre would encompass the entirety of our solar system. "Sagittarius A* is over 1,000 less massive than the black hole at M87," said radio astronomer Lindy Blackburn, an EHT data scientist at the Harvard-Smithsonian Centre for Astrophysics. "But since it is in our own galaxy it is much closer, and should appear just slightly larger on the sky. "However, the smaller physical size of Sgr A* also means that everything changes about a thousand times faster for Sgr A* than M87. "We must also peer through the messy disc of our own galaxy to view Sgr A*, which blurs and distorts the image." The Event Horizon Telescope is a global network of observatories collaborating to observe radio sources associated with black holes. The project was begun in 2012 to try to directly observe the immediate environment of a black hole. There are different categories of black holes. The smallest are so-called stellar-mass black holes formed by the collapse of massive stars at the ends of their life cycles. There also are intermediate-mass black holes, which have larger mass. And finally there are the supermassive black holes that inhabit the centre of most galaxies. These are thought to arise relatively soon after their galaxies are formed, devouring enormous amounts of material to achieve colossal size. Thursday's announcement was made simultaneously in the US, Germany, China, Mexico, Chile, Japan and Taiwan.
