A black hole that goes the distance - Astronomy - Brief Article

Science News, May 17, 2003

The mass of the most distant black hole known has been measured, and it's a behemoth. The black hole lies some 13 billion light-years away and weighs the equivalent of 3 billion suns, researchers report in the April 10 Astrophysical Journal Letters.

To weigh the hole, astronomers examined light from the most remote quasar ever detected. According to theory, quasars are powered by supermassive black holes. Specifically, a quasar's brilliant light would come from the radiation released when material falls onto a rotating disk of gas surrounding a black hole.

Using the United Kingdom Infrared Telescope atop Hawaii's Manna Kea, researchers took a spectrum of the quasar light and identified radiation emitted by magnesium ions in the black hole's swirling disk. Each type of ion emits light at a specific wavelength, which under tamer conditions would show up as a narrow line in the quasar's spectrum. But the velocity of the rotating disk broadens each line of emitted radiation. The more massive the black hole, the higher the disk's velocity and the greater the broadening.

By measuring the width of the magnesium-ion emission line, Chris Willott of the Herzberg Institute of Astrophysics in Victoria, Canada, and his colleagues deduced the disk's velocity, enabling them to calculate the black hole's mass.

The finding indicates that heavyweight black holes existed 13 billion years ago, when the universe was a mere babe. Using the same technique, the team hopes to determine the mass of supermassive black holes over a range of cosmic times. Because of close connections between supermassive black holes and the cores of the galaxies in which the holes reside, measurements of these masses may reveal new details about how galaxies evolve.--R.C.