Possible direct evidence has been provided illustrating the theory that the earliest galaxies developed quickly -- and to surprisingly massive proportions -- with the help of mysterious and invisible dark matter.

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Mystery Matter Helped Build First Galaxies, Study Suggests
By Robert Roy Britt
Senior Science Writer
In Space.com posted: 02:00 pm ET 22 January 2003

Possible direct evidence has been provided illustrating the theory that the earliest galaxies developed quickly -- and to surprisingly massive proportions -- with the help of mysterious and invisible dark matter. The evidence supports a growing understanding among astronomers about galactic origins.

The results come from a new and inventive computer model crunching data from recent observations of the farthest known light sources.

In the past few years, astronomers have glimpsed compact but brilliant objects, called quasars, populating the early universe. Most experts agree that the brightest quasars detected so far are powered by central black holes with masses equal to a billion suns or more. But the mass-estimation techniques are not well developed because quasars have proved difficult to decipher.

Bright quasar emissions drown out what`s going on within and nearby, so researchers have also struggled to take a measure of any surrounding galaxy they think should feed the central black hole with gas. Sorting out how the whole setup is structured has resulted in little more than speculation.

The new model explains curious a feature seen in light from two quasars determined in other studies to be roughly 13 billion light-years away, or within 1 billion years of the Big Bang. When a quasar`s central black hole swallows gas, it converts some of it to energy, creating vivid emissions of radio waves, x-rays and other forms of light.

The new analysis shows that hydrogen gas falling into a quasar`s host galaxy absorbs some of the quasar`s light, and that this infall can be used to measure the host galaxy`s mass.

The two quasar galaxies are about the same size as our Milky Way, the study found.

"This is the first time that the mass of an early galaxy has been directly measured," said Rennan Barkana of Tel Aviv University. The results will be detailed in the Jan. 23 issue of the journal Nature.

Barkana`s co-author, Abraham Loeb, explained their interpretation of the observations, which were originally made as part of the Sloan Digital Sky Survey. Loeb is a professor at the astronomy department of Harvard University is currently on sabbatical at the Institute for Advanced Study in Princeton, New Jersey.

The galaxy pulls in gas from its vicinity, Loeb said. A small fraction of neutral hydrogen atoms in the gas absorb the quasar`s light. Because the gas falls toward the quasar and away from us, its light waves are stretched by a noticeable amount toward the red end of the spectrum, a phenomenon called redshift. This redshift shows up in addition to the cosmological redshift of the entire quasar.

"The speed of the infalling gas can be, in principle, inferred from this additional redshift," Loeb said. It is moving at about 1.1 million mph (500 kilometers per second).

The analysis supports the widely held assumption that the brightest quasars known are super-sized black holes containing the mass of a billion or more suns, Loeb told SPACE.com. It also supports the increasingly solid case that black hole mass and its galaxy`s rotational velocity are intimately connected.

The observations point to another, even more intriguing idea.

Scientists have long puzzled over the fact that such massive light engines formed in the first 5 to 10 percent of the universe`s age. One contributing factor seems to be a halo of dark matter surrounding the host galaxy of the black hole, which allows it to draw large quantities of gas from its environment, Loeb said. Dark matter can not be seen directly, but astronomers infer its existence from the gravitational effects it has on the internal dynamics of galaxies.

The amount of information gathered from the most distant objects has never allowed a firm determination of dark matter`s presence in galaxies of the early universe. Loeb and Barkana say more observations are needed to confirm their results.

"If this signature is confirmed, it would provide the first observational evidence that quasars are embedded in great haloes of dark matter," said Laura Ferrarese, a Rutgers University physicist who was not involved in the research.

In a telephone interview, Ferrarese said dark matter is gaining wide acceptance as a catalyst in the development of black holes and the structure of galaxies.

Ferrarese said quasars that are closer to us in space and time have been examined in some detail, but Barkana and Loeb have provided the first glimpse of the anatomy of the most distant known quasars.

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