New detection method to double number of known black holes

Scientists have developed a new method that will detect roughly ten black holes per year, doubling the number currently known within two years, and unlock their history in a little more than a decade.
Researchers from the University of Waterloo in Canada came up with the method that has implications for the emerging field of gravitational wave astronomy and the way in which we search for black holes and other dark objects in space.
"Within the next ten years, there will be sufficient accumulated data on enough black holes that researchers can statistically analyse their properties as a population," said Avery Broderick, professor at the University of Waterloo.

"This information will allow us to study stellar mass black holes at various stages that often extend billions of years," said Broderick.
Black holes absorb all light and matter and emit zero radiation, making them impossible to image, let alone detect against the black background of space.
Although very little is known about the inner workings of black holes, we do know they play an integral part in the lifecycle of stars and regulate the growth of galaxies.

The first direct proof of their existence was announced earlier this year by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US when it detected gravitational waves from the collision of two black holes merging into one.

"We do not yet know how rare these events are and how many black holes are generally distributed across the galaxy," said Broderick.
"For the first time we will be placing all the amazing dynamical physics that LIGO sees into a larger astronomical context," he said.
Researchers propose a bolder approach to detecting and studying black holes, not as single entities, but in large numbers as a system by combining two standard astrophysical tools in use today: microlensing and radio wave interferometry.
Gravitational microlensing occurs when a dark object such as a black hole passes between us and another light source, such as a star.

The star's light bends around the object's gravitational field to reach Earth, making the background star appear much brighter, not darker as in an eclipse.
Even the largest telescopes that observe microlensing events in visible light have a limited resolution, telling astronomers very little about the object that passed by.
Instead of using visible light, Broderick and his team propose using radio waves to take multiple snapshots of the microlensing event in real time.
The study was published in The Astrophysical Journal.