For years, astronomers speculated that a giant, mysterious force lay at the center of the Milky Way, but it wasn’t until four years ago that UCLA astronomer Andrea Ghez definitively showed what it was.
Using new techniques for peering into the dusty heart of the galaxy, Ghez’s observations proved that scores of stars were rapidly orbiting what could only be a black hole. But it wasn’t the kind of garden-variety black hole created when a star explodes and dies; it was hundreds of thousands of times as powerful – a “supermassive” black hole, as they are now known.
Her discoveries, along with the work of scientists studying other galaxies, have in a short time led researchers to the surprising conclusion that most, if not all, of the universe’s hundreds of billions of galaxies have supermassive black holes at their cores. Even more striking, the astronomers have found that the black holes’ mass and nature are closely related to the size and makeup of the surrounding galaxies.
It also appears that these cosmic monsters – which can “eat” stars whole – are key to understanding how galaxies were formed and are still being formed today.
“Many of these discoveries were unexpected,” said Ghez, a self-described “telescope junkie” and rising astronomy star who does much of her galaxy- gazing at the W.M. Keck Observatory in Hawaii, site of the world’s largest optical telescope. “There’s tremendous interest in this field now because of the potential that it can tell us so much about the dynamics of very basic galaxy creation.”
Black holes appear, for instance, to be both creators and destroyers – swallowing stars or gases that come too close while also spewing out jets of super-high-energy particles and radiation generated by this violent feeding process. The jets, which can be millions of light-years in length, are believed to seed galaxies with the mass and energy that will, in time, become new stars and perhaps even planets.
With many promising areas to research, the supermassives are drawing astronomers and astrophysicists back into black-hole research.
The Hubble Space Telescope provided the first real evidence of the existence of supermassive black holes – revealing in 1994 that something was orbiting rapidly around the nuclei of some distant galaxies, suggesting the presence of a huge mass contained in a very small area.
Since then, the Hubble, NASA’s orbiting Chandra X- Ray Observatory, the Keck and other very large, high-resolution ground telescopes have begun to unravel more about these central black holes – which can be as large as the distance from the sun to well past Mars and as small as New Jersey.
To the enormous surprise of those who study the universe, the size of a supermassive black hole appears to have a direct and unusual correlation to the galaxy around it. This relationship supports the notion that the evolution and structure of a galaxy is closely tied to the scale of its black hole.
“This is an exciting new wrinkle on the old concept of black holes, and that’s why so many researchers are drawn to it,” said astrophysicist Juna Kollmeier.
