(WHTM) — Quasar is short for quasi-stellar object. When it was first coined in the 1960s, though, it was short for quasi-stellar radio source, because they were objects that looked like stars in visible light but were found to be emitting powerful radio waves when observed with radio telescopes. And just recently astronomers, using six different telescopes, including the Hubble Space Telescope, found something spectacular – a double quasar system, formed by the collision of two galaxies 10 billion years ago.
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We now know what quasars are. (Well, most of them anyway.) They are black holes, places where gravity collapses matter to infinite density, so nothing can escape them-not even light. But if the black holes themselves are not emitting any light, where are all the light and radio waves coming from?
Black holes are voracious feeders, sucking up anything nearby. This includes lots of dust and gas, which gets heated to incredibly high temperatures, producing light. (Remember, visible light and radio waves are both parts of the same electromagnetic spectrum.) But the material doesn’t fall into black holes at a constant rate, with the result that the light from a quasar will “flicker”.
The galaxy astronomers were observing had two different rates of flickering. That suggested there were two black holes in close proximity to each other. When they pointed NASA’s Hubble Space Telescope at the object, It captured two circles of light.
Refining the data required observations from other telescopes: the W.M. Keck Observatories in Hawaii, the International Gemini Observatory in Hawaii, NSF’s Karl G. Jansky Very Large Array in New Mexico, NASA’s Chandra X-ray Observatory, and the European Space Agency’s Gaia space observatory.
The observations confirmed scientists were looking at two quasars on a collision course with each other, embedded in a pair of galaxies that smashed into each other 10 billion years ago or, to put it another way, when the universe was a mere 3 billion years old. As graduate student Yu-Ching Chen of the University of Illinois at Urbana-Champaign, the lead author of this study, explains, “We don’t see a lot of double quasars at this early time in the universe. And that’s why this discovery is so exciting,”
Scientists now believe large galaxies grow by the merging together of smaller systems. The mergers should produce pairs of supermassive black holes. “Knowing about the progenitor population of black holes will eventually tell us about the emergence of supermassive black holes in the early universe, and how frequent those mergers could be,” said Chen.
Xin Liu of the University of Illinois at Urbana-Champaign points out this study contains two important advances. “It is actually telling us that this population exists, and now we have a method to identify double quasars that are separated by less than the size of a single galaxy.”
Of course, this double quasar no longer exists. During the 10 billion years that it took for their light to reach our telescopes, the two galaxies have likely shaped themselves into a giant elliptical galaxies, like the ones seen in the local universe today. The quasars too have merged, becoming a single mind-bogglingly huge supermassive black hole.