University of Washington

Jun. 10, 1998

Brightest object in universe discovered by UW astronomer

The brightest object yet observed in the universe has been discovered by a University of Washington astronomer and his colleagues.

The quasar (or quasi-stellar object) is 4 million-billion to 5 million-billion times brighter than the Sun. It is estimated to be more than 10 times brighter than any other quasar, and outshines the brightest galaxy by more than 100 times.

The research is described in the June 11 edition of the British journal Nature, and the findings have been accepted for publication in Astrophysical Journal.

Geraint Lewis, a postdoctoral researcher at the UW, along with his collaborators, made the discovery in observations taken with the 2.5-meter Isaac Newton Telescope at La Palma in the Canary Islands, and also on the 1-meter Jacobus Kapteyn Telescope at La Palma. Lewis' colleagues include Michael Irwin of the Royal Greenwich Observatory, Rodrigo Ibata of the European Southern Observatory in Munich, and Edward Totten of Queens University, Belfast.

The object is scheduled for observation by the Hubble Space Telescope in the near future. Its brightness actually comes from two different sources. Light in the ultraviolet and optical range comes from what is known as an accretion disk surrounding a supermassive black hole. A supermassive black hole has millions of times the mass of the Sun. Matter from stars and other objects attracted by the black hole's gravity generates energy (including light) from friction as it is torn apart and falls toward the black hole.

The second source of brightness, in the infrared portion of the spectrum, comes from thick dust heated by radiation from the center of the quasar. "In most of these ultraluminous galaxies, dust is the source of most of the energy," Lewis says. "But in this quasar, about half comes from the accretion disk."

Quasars are some of the most energetic objects observed in the universe. Each quasar generates more energy than the rest of a galaxy's stars combined. Yet a quasar, the black hole and its surrounding accretion disk occupy a relatively small amount of space, galactically speaking -- not much larger than our solar system.

The quasar observation occurred by accident. The team was studying the Sagittarius Dwarf Galaxy's interaction with our own. They were observing stars in the halo of our galaxy when this very bright object showed up in one observation.

"It was actually a serendipitous discovery, as the best discoveries often are," Lewis said.

The quasar is estimated to be 11 billion light years from Earth. Light being received now on Earth emanated from the quasar when the universe was only about 10 percent of its present age.

Finding an object of this energy level could help scientists understand more about what fuels quasars. Lewis and his colleagues are trying to gather more data, including high-resolution images, to develop an understanding of the complete spectrum of energy from this object. "Then we can apply physics to the various components, which should tell us more about what's happening in the quasar," he said. Ultimately, information like this helps astronomers develop a more accurate picture of the universe's origins and its structure.

Further study could show that the apparent energy level of the quasar is being magnified by a gravitational lens. Gravitational lenses are often seen to be the cause of extremely bright objects. Typically, such a lens might exaggerate the real energy level by a factor of 30 or 40 -- but even taking that into account, this galaxy would outshine our own by more than 1,000 times.

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