WASHINGTON: Scientists have provided the first look at the “gentle giant” lurking at the centre of our Milky Way galaxy – an image of a supermassive black hole that devours any matter within its huge gravitational pull.
The black hole – called Sagittarius A*, or Sgr A* – is the second one ever to be imaged. The feat was accomplished by the same Event Horizon Telescope (EHT) international collaboration that in 2019 unveiled the first photo of a black hole – that one residing at the heart of a different galaxy.
At a news conference in Washington on Thursday, University of Arizona astronomer Feryal Ozel hailed “the first direct image of the gentle giant in the center of our galaxy,” showing a glowing ring of red, yellow, and white surrounding a darker center.
Sagittarius A* (pronounced Sagittarius “A” star) possesses 4 million times the mass of our sun and is located about 26,000 light-years – the distance light travels in a year, 5.9 trillion miles (9.5 trillion km) – from Earth.
Harvard-Smithsonian Center for Astrophysics astrophysicist Michael Johnson called Sagittarius A* “ravenous but inefficient,” currently eating relatively little matter. “If Sgr A* were a person, it would consume a single grain of rice every million years,” Johnson said. It is putting out only a few hundred times the energy of the sun despite being much more massive.
Black holes are extraordinarily dense objects with gravity so strong that not even light can escape, making viewing them extremely 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 – gets dragged into oblivion.
The image was obtained using the EHT’s global network of observatories working collectively to observe radio sources associated with black holes. It showed a ring of light – super-heated disrupted matter and radiation circling at tremendous speed at the edge of the event horizon – around a region of darkness representing the actual black hole. This is called the black hole’s shadow or silhouette.
Imaging it was complicated by its dynamic environment including swirling gas around it – as Özel put it: “a source that burbled and gurgled as we looked at it.” “We love our black hole,” Ozel said.
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 situated on one of the spiral arms and Sagittarius A* located at the center.
Scientists are trying to better understand how supermassive black holes form early in a galaxy’s history and evolve over time. The image released in 2019 showed the supermassive black hole in a galaxy called Messier 87, or M87. That one was far more distant and massive than Sagittarius A*, situated about 54 million light-years from Earth with a mass 6.5 billion times that of our sun.
Sagittarius A*, despite being much closer to our solar system than M87, was harder to image. The diameter of Sagittarius A* is about 17 times that of the sun, meaning it would sit within the innermost planet Mercury’s solar orbit. In contrast, M87’s diameter would encompass the entirety of our solar system.
The announcement was made in news conferences at seven sites worldwide. EHT Project Director Huib Jan van Langevelde in Germany voiced excitement over finally unmasking the enigma that had been Sagittarius A*.