Quasar Wins Title 'Most Distant in the
Quasar Wins Title 'Most Distant in the
Posted March 1, 2000
If Guinness had a Book of Cosmic Records, a newly discovered quasar in the constellation Cetus would make the front page. This distant quasar easily skates past the previous record-holder, placing it among the earliest known structures ever to form in the universe.
A team of astronomers identified the candidate after nights of deep, long-exposure imaging at the California Institute of Technology's five-meter Hale Telescope at Palomar Observatory in California and at the National Science Foundation's four-meter Mayall Telescope at Kitt Peak, Ariz. A spectral analysis of the quasar's light was then completed at the 10-meter Keck Observatory telescope in Hawaii.
"As soon as we saw the spectrum, we knew we had something special," said Daniel Stern, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, who played a key role in the discovery. "In images, quasars can look very much like stars, but a spectral analysis of a quasar's light reveals its true character. This quasar told us that it was 'an ancient' -- one of the universe's first structures."
Quasars are extremely luminous bodies that were more common in the early universe. Packed into a volume roughly equal to our solar system, a quasar emits an astonishing amount of energy -- up to 10,000 times that of the whole Milky Way galaxy. Scientists believe that quasars get their fuel from super-massive black holes that eject enormous amounts of energy as they consume surrounding matter.
"This one is unusual in that it is emitting a lot of ultraviolet light, considering how young it is," said Hyron Spinrad, professor of astronomy at Berkeley, and the leader of the observing group. "It's less than a billion years old, so it had to have grown its central black hole very fast, faster than the one solar mass per year we estimate for most quasars."
A quasar's "redshift" measures how fast the object is moving away from us as the universe expands, and is a good indicator of cosmic distances. The faster it moves away, the more its light shifts to the red part of the spectrum (toward longer wavelengths). The quasars ultraviolet emissions have been redshifted into the far red part of the visible spectrum, almost into the infrared.
Because the faster an object appears to move, the farther away it is, at a redshift of 5.5, light traveling from Stern's quasar has journeyed about 13 billion years to get here. That means the quasar existed at a time when the universe was less than 8 percent of its current age.
"The odds against us finding a quasar at a redshift of 5.5 were fairly large, especially when you consider how small a portion of the sky we were observing -- 10 by 10 arcminutes. To get an idea of how small that is, try holding a dime at arms-length against the night sky; it's roughly the size of FDR's ear," said Stern. Until the last few years, no one had discovered an object that came close to a redshift of 5.0.
High-redshift quasars are vitally important to understanding one of the biggest mysteries confronting scientists: how the universe went from the smooth uniformity of its youth to the clumpy, galaxy-strewn formations we observe today. Astronomers believe that the young universe began in a hot, dense state shortly after the Big Bang. Matter in the universe was ionized back then, meaning that electrons were not bound to protons. As the universe aged, matter cooled enough for electrons and protons to combine, or to become neutral. As the first stars and galaxies formed, they reheated matter between galaxies, creating the ionized intergalactic medium we see today in our local universe. The million-dollar question for today's cosmologists is when this second transition from neutral to ionized gas occurred.
Analyzing the spectrum of the new quasar will be very useful for testing whether the universe was neutral or ionized at redshift 5.5. As a quasar's light makes its journey toward us, the light is absorbed by any matter that lies in its path. Scientists have learned that clouds of neutral hydrogen absorb more than half of a quasar's light at high redshift (in the early universe). That finding is central to understanding when and how super-massive black holes, quasars and other structures condensed from large, high-density clouds of hydrogen soon after the Big Bang. The new quasar will also shed light on how matter was distributed at earlier stages of cosmic history.
"Finding a quasar at this distance is like turning on a flashlight at the edge of the universe," said Stern. "Because quasars are more luminous than distant galaxies at the same redshift, they act as the brightest flashlights, allowing us to study everything that has ever developed between us and the quasar."