The black hole – called Sagittarius A* or Sgr A* – is the second hole ever photographed. The feat was accomplished by the same international collaboration Event Horizon Telescope (EHT) that in 2019 revealed the first image of a black hole – that image living in the heart of a different galaxy.
At a press conference in Washington, University of Arizona astronomer Ferial Ozil hailed the “first direct image of the gentle giant at the center of our galaxy,” which shows a glowing ring of red, yellow and white surrounding a darker center.
Sagittarius A* (called the Sagittarius “A” star) has a mass 4 million times the mass of our Sun and is located 26,000 light-years away – the distance light travels in a year, 9.5 trillion km – from Earth.
Michael Johnson, an astrophysicist at the Harvard-Smithsonian Center, called Sagittarius A* a “predatory but inefficient,” as it currently eats relatively little matter.
“If Sgr A* was a person, he would consume one grain of rice every million years,” Johnson said.
It only emits a few hundred more energy from the Sun despite being much larger.
What are black holes?
Black holes are unusually dense objects with such strong gravitational force that not even light can escape, making them extremely difficult to view. The event horizon of a black hole is the point of no return beyond which anything — stars, planets, gas, dust, and all forms of electromagnetic radiation — is dragged into oblivion.
The image was acquired using the EHT’s global network of observatories that work collectively to monitor radio sources associated with black holes.
He showed a ring of light – intermittent superheated matter and radiation circling at tremendous speed at the edge of the event horizon – around a dark region representing the actual black hole. This is called a black hole’s shadow or silhouette.
Its depiction was complicated by its dynamic environment including swirling gas around it, or as Ozil put it: “a source that was flopping and gurgling when we looked at it.”
“We love our black hole,” Ozil said.
The Milky Way is a spiral galaxy containing at least 100 billion stars. Viewed from above or from below, it is like a rotating propeller, with our Sun located on one of the spiral arms and the A* arc in the center.
“Just drops in.”
Scientists are trying to better understand how supermassive black holes formed early in galactic history and evolved over time.
“They go through periods where there is a lot of material around them,” Ozil said.
“…and then they go through these quiet phases like the one at the center of our galaxy where matter seeps in.”
An image released in 2019 showed the presence of a supermassive black hole in a galaxy called Messier 87, or M87. This object was much farther and more massive than Sagittarius A*, which is located about 54 million light-years from Earth and has a mass 6.5 billion times the mass of our Sun.
Despite being closer to our solar system than M87, it was difficult to photograph. Sagittarius A* is about 17 times the diameter of the Sun, which means that it will lie within the solar orbit of the innermost planet Mercury.
In turn, the diameter of M87 would include our entire solar system.
Push telescopes to breaking point
“Sgr A*’s smaller physical size also means that everything is changing about a thousand times faster for Sgr A* than M87,” said radio astronomer Lindy Blackburn of the Harvard-Smithsonian Center for Astrophysics. “We must also study the chaotic disk of our galaxy to view Sgr A.” The one who blurs and distorts the image.
Johnson said the two images of the black hole appear blurry because obtaining them has pushed the power of telescopes “to the breaking point”. Vincent Fish, an astronomer at the Haystack Observatory at MIT, said the researchers hope to obtain video of the M87 black hole in the future.
Thursday’s announcement came at press conferences in seven locations worldwide.
EHT project manager Huib Jan van Langevelde in Germany is pleased to finally unveil the mystery that was Sagittarius A*.
“I think it’s very exciting,” said Kate Bowman, a computer scientist at the California Institute of Technology. “What’s better than seeing the black hole at the center of our Milky Way?”