The measure of a black hole is what it does with its stars.
Thats one lesson astronomers are taking from the first-ever picture of a black hole, released on April 10 by an international telescope team (SN Online: 4/10/19). That image confirmed that the mass of the supermassive black hole in the center of galaxy M87 is close to what astronomers expected from how nearby stars orbit — solving a long-standing debate over how best to measure a black holes mass.
The black hole in M87, which is located about 55 million light-years from Earth, is the first black hole whose mass has been calculated by three precise methods: measuring the motion of stars, the swirl of surrounding gases and now, thanks to the Event Horizon Telescope imaging project, the diameter of the black holes shadow.
In 1978, the first mass estimates to track the motions of stars whipping around the great gravitational center found that the stars must be orbiting something containing about 5 billion times the mass of the sun. A more precise estimate in 2011 using a similar stellar technique bumped its heft up to 6.6 billion times the mass of the sun.
Meanwhile, astronomers in 1994 made another estimate by tracing how gases closer to the black hole than the stars swirl around the behemoth. That technique suggested that the black hole was 2.4 billion solar masses, which was revised in 2013 to 3.5 billion solar masses.
For years, it wasnt clear which technique got closer to the truth.
Now the EHT picture showing a glowing orange ring of gases and dust around the black hole has solved the conflict. According to Einsteins general theory of relativity, the diameter of the dark space in the center of the image — the black holes shadow — is directly related to its mass.
“Bigger black holes cast bigger shadows,” EHT team member Michael Johnson, an astrophysicist at the Harvard Smithsonian Center for Astrophysics, said April 12 at a talk at MIT. “Easy check, we can see whether one or the other of these [mass measuring methods] is correct.” The shadow of M87s black hole yielded a diameter of 38 billion kilometers, which let astronomers calculate a mass of 6.5 billion suns — very close to the mass suggested by the motion of stars.
The size of the shadow also negated the idea that the black hole is a wormhole, a theoretical bridge between distant points in spacetime (SN: 5/31/14, p. 16). If M87s black hole had been a wormhole, theory predicts it should look smaller than it does. “Its a stunning confirmation” of general relativity, Johnson said. “We instantly rule out all these exotic possibilities.”
The mass confirmation may boost confidence in current simulations for how black holes develop, says Priyamvada Natarajan, a Yale University astrophysicist who was not involved with the EHT project. Most black hole mass estimates already use the stellar technique, in part because its easier to track a galaxys stars from farther away.
The measure of a black hole is what it does with its stars.
Thats one lesson astronomers are taking from the first-ever picture of a black hole, released on April 10 by an international telescope team (SN Online: 4/10/19). That image confirmed that the mass of the supermassive black hole in the center of galaxy M87 is close to what astronomers expected from how nearby stars orbit — solving a long-standing debate over how best to measure a black holes mass.
The black hole in M87, which is located about 55 million light-years from Earth, is the first black hole whose mass has been calculated by three precise methods: measuring the motion of stars, the swirl of surrounding gases and now, thanks to the Event Horizon Telescope imaging project, the diameter of the black holes shadow.
In 1978, the first mass estimates to track the motions of stars whipping around the great gravitational center found that the stars must be orbiting something containing about 5 billion times the mass of the sun. A more precise estimate in 2011 using a similar stellar technique bumped its heft up to 6.6 billion times the mass of the sun.
Meanwhile, astronomers in 1994 made another estimate by tracing how gases closer to the black hole than the stars swirl around the behemoth. That technique suggested that the black hole was 2.4 billion solar masses, which was revised in 2013 to 3.5 billion solar masses.
For years, it wasnt clear which technique got closer to the truth.
Now the EHT picture showing a glowing orange ring of gases and dust around the black hole has solved the conflict. According to Einsteins general theory of relativity, the diameter of the dark space in the center of the image — the black holes shadow — is directly related to its mass.
“Bigger black holes cast bigger shadows,” EHT team member Michael Johnson, an astrophysicist at the Harvard Smithsonian Center for Astrophysics, said April 12 at a talk at MIT. “Easy check, we can see whether one or the other of these [mass measuring methods] is correct.” The shadow of M87s black hole yielded a diameter of 38 billion kilometers, which let astronomers calculate a mass of 6.5 billion suns — very close to the mass suggested by the motion of stars.
The size of the shadow also negated the idea that the black hole is a wormhole, a theoretical bridge between distant points in spacetime (SN: 5/31/14, p. 16). If M87s black hole had been a wormhole, theory predicts it should look smaller than it does. “Its a stunning confirmation” of general relativity, Johnson said. “We instantly rule out all these exotic possibilities.”
The mass confirmation may boost confidence in current simulations for how black holes develop, says Priyamvada Natarajan, a Yale University astrophysicist who was not involved with the EHT project. Most black hole mass estimates already use the stellar technique, in part because its easier to track a galaxys stars from farther away.
