Near the centre of the Milky Way Galaxy sits an immense “supermassive” black hole that astronomers call Sagittarius A*.
Scientists theorise that the black hole grew in tandem with our galaxy, and suspect that similar phenomena are at the heart of most large galaxies in the universe.
Sagittarius A* is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, visually close to the Butterfly Cluster (M6) and Lambda Scorpii.
The Event Horizon Telescope Collaboration unveiled the first picture of Sagittarius A* on May 12th, 2022. The image was constructed from radio interferometer data gathered in 2017, confirming for the first time the presence of a black hole within the centre of the object.
According to a study by Joseph Simon, postdoctoral researcher in the Department of Astrophysical and Planetary Science at the University of Colorado Boulder, “The black hole at the centre of our galaxy is millions of times the mass of the sun, but we also see others that we think are billions of times the mass of the sun.”
““We have really good measurements for the masses of the supermassive black holes for our own galaxy and for galaxies close by. We don’t have those same kinds of measurements for galaxies farther away. We just have to guess,” added Simon.
The astrophysicist is part of a second research effort called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Through the project, Simon and hundreds of other scientists in the U.S. and Canada have spent 15 years searching for a phenomenon known as the “gravitational wave background.” The concept refers to the steady flow of gravitational waves, or giant ripples in space and time, that undulate through the universe on a near-constant basis.
To understand the gravitational wave background, however, scientists first need to know how massive the universe’s supermassive black holes really are.
Simon gathered information about hundreds of thousands of galaxies, some billions of years old. (Light can only travel so fast, so when humans observe galaxies that are farther away, they’re looking back in time). Simon used that information to calculate the approximate black hole masses for the largest galaxies in the universe. He then employed computer models to simulate the gravitational wave background those galaxies might create and that currently washes over Earth.
Simon’s results reveal the full smorgasbord of supermassive black hole masses in the universe dating back roughly 4 billion years. He also noticed something odd: There seemed to be a lot more large galaxies spread throughout the universe billions of years ago than some previous studies have predicted.
“There’s been the expectation that you would only see these really massive systems in the nearby universe,” Simon said. “It takes time for black holes to grow.”
Header Image Credit : EHT Collaboration – CC BY 4.0