Astronomers get peek at first galaxies

By LIDIA WASOWICZ, UPI Senior Science Writer   |   Jan. 22, 2003 at 2:00 PM

Astronomers said Wednesday they have peered to nearly the beginning of the universe to see a signature of the first galaxies.

They gathered evidence of a host of massive star systems surrounding the earliest generation of quasars -- distant and luminous celestial objects that emit up to 1,000 times the energy of the Milky Way Galaxy but are no larger than the solar system.

"Astronomers are studying some of the first galaxies that formed in the universe," study co-author Rennan Barkana, assistant professor of astronomy and astrophysics at Tel Aviv University in Israel, told United Press International. "These investigations are yielding clues about the structure of the universe and about the formation process of galaxies, including our own Milky Way."

Barkana and colleagues began their research after seeing results in 2001 from the Sloan Digital Sky Survey. The project at the Apache Point Observatory in Sunspot, N.M., will make a detailed map of one-quarter of the sky, determining the positions and brightness of more than 100 million celestial objects and measuring the distances to more than 1 million galaxies and quasars.

Observations with specially designed telescopes revealed a thriving community of black holes -- objects so dense that light cannot escape -- 1 billion years after the birth of the universe.

Astronomers found it difficult to explain how objects 1 billion times the mass of the sun could have formed in such short order.

"Quasars, the oldest known objects in the universe, are powered by gas falling into black holes at their centers," said Laura Ferrarese of the Department of Physics and Astronomy at Rutgers University in Piscataway, N.J. "How black holes formed so early in time has been hard to explain but a new model might have the answer."

Barkana and colleagues detected the signature imprint of the streams of gas the feed into black holes and account for their rapid growth. They say the finding provides the first observational evidence for galaxies that are home to the earliest generation of quasars.

"Our study shows that the most luminous quasars in the early universe form in massive galaxies, more massive than our own Milky Way Galaxy," lead study author Abraham Loeb, professor of astronomy at Harvard University in Cambridge, Mass., told UPI.

The brilliant mirrors of the distant past -- larger than stars and found in the centers of galaxies that glow with the intensity of 10 trillion suns -- are fueled by gargantuan black holes millions to billions of times more massive than the sun.

Stars and interstellar gas are drawn into the black hole, sending a final burst of light at nearly all wavelengths of the electromagnetic spectrum. Such super massive black holes are estimated to swallow the equivalent of 10 to 20 stars each year.

Analyzing how atoms absorb and emit light in the electromagnetic radiation, through a process called spectroscopy, provides astronomers with a unique ability to "fingerprint" very high energy objects at great distances.

The technology seems perfect for researchers looking into the very edges of space and time. By determining the properties of the oldest, brightest and farthest celestial objects, they can learn of the dawning of the universe.

"The early universe holds important clues about our origins. The fundamental question of how the first sources of light formed was addressed in religious texts for many centuries," Loeb said. "Now, for the first time in human history, we have the technology to answer this question scientifically."

By looking far away, astronomers learn of the origins of quasars and galaxies.

"Quasars (short for quasi stellar objects, reflecting their star-like appearance) are ... among the most distant objects known to astronomers," Ferrarese said. "As such, the light reaching the Earth from them paints an invaluable picture of the history of our universe."

To explain galaxy formation, scientists use a "hierarchical" model, in which small star clusters appear then merge or siphon off gas from their surroundings to expand into larger systems.

"However, distant galaxies are very faint and hard to study," Barkana said. "Our findings offer the first potential method for weighing distant galaxies."

The investigators identified the signature of the galaxy-quasar relationship.

"The massive galaxy that hosts the quasar pulls gravitationally large quantities of gas from its surroundings," Loeb explained. "The in-falling cosmic gas absorbs some of the quasar light. Based on the associated absorption signature, we can infer how much mass of gas is falling onto the host galaxy of the quasars, and from that we can estimate its total mass."

Astronomers gauge an object's distance from Earth by measuring its redshift -- the amount by which its light waves are stretched, or shifted toward the red part of the spectrum, as it moves away in the expanding universe. The higher the redshift, the more distant and ancient the object.

The current record-holder, a quasar with a redshift of 6.4, is seen as it was when the universe was about 800 million years old, or roughly 5 percent of its current age, which is estimated at between 11.2 billion and 20 billion years. It took the light from the quasar some 13 billion years to reach Earth.

More than 10,000 of the brilliant objects have been identified since the first quasar redshift -- of 0.16 -- was measured in 1963.

In addition to revealing the distribution of luminous matter in the early universe, distant quasars provide information about some types of "dark matter" that fills intergalactic space.

The researchers' goal is to develop a tool for measuring the masses of the unseen matter that make up the bulk of the universe, Barkana said.

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