Scientists led by a Pasadena astronomer said Tuesday they have used an extraordinarily long exposure from the Hubble Space Telescope to create sharp images of a 4-billion-year-old galaxy cluster that confirms theories that the universe is evolving--"and at a pretty rapid rate."
At the same time, in the background of those images, the astronomers serendipitously stumbled upon what appears to be a previously unknown, 10-billion-year-old galaxy cluster. When studied further, that cluster may answer fundamental questions about how and why galaxies formed.
Along with other recent finds, the images should help partially rehabilitate the Hubble's reputation. The $1.5-billion space telescope had been written off as "virtually blind" after the National Aeronautics and Space Administration found a fundamental flaw in its main imaging mirror after its 1990 launch.
Salvaging images from the Hubble's current wide-field and planetary camera--an updated model is scheduled to be installed late next year--has not been simple, but it is possible, said Alan Dressler of Pasadena, the Carnegie Institution astronomer who announced the findings Tuesday.
For example, Dressler's team kept the space telescope fixed on one spot for six hours spread over 10 Earth orbits just to gather enough light to see the galaxy cluster clearly. Even then, the images had to be enhanced by computer to produce the photographs made public on Tuesday in Washington.
Daniel Weedman, an astronomy professor at Pennsylvania State University, praised the effort behind the discovery as "almost heroic."
These new images--produced by Dressler, Augustus Oemler of Yale University, James E. Gunn of Princeton University and Harvey Butcher of the Netherlands Foundation for Research in Astronomy--show some galaxies colliding and violently ripping one another apart. This phenomenon, which astronomers refer to as a "cosmic Cuisinart," could explain how some galaxies evolve.
"We have actually seen galaxies change over time. That's very important to proving the Big Bang theory," said Dressler, a pioneer in studying the morphology, or structure, of galaxies. "The universe was a much different place even 4 billion years ago than it is today. . . . The universe is evolving, and at a pretty rapid rate."
Other astronomers were equally enthusiastic about the images of the distant galaxies, which are so far away that light from them has taken 4 billion years to reach Earth--and, thus, give scientists the opportunity to see how those galaxies appeared about the time our own Milky Way galaxy was created.
"It's like we are truly in a time machine with the Hubble telescope," Weedman said.
"For the very first time, we can see 'before' and 'after' pictures of the universe," said Bruce Margon, chairman of the University of Washington's astronomy department. "Things people have been speculating about for 20 or 30 years--here, with one picture, the Hubble proved to be true."
Dressler said that nearly 30% of the 4-billion-year-old galaxies photographed by the Hubble are spiral-shaped. That is six times the percentage found in galaxies today, Dressler said.
This finding, based on direct photographic evidence made possible with the space telescope, confirmed a postulation first advanced by Butcher and Oemler in 1978. At that time, they noted that distant clusters seemed to contain a higher percentage of hot, "blue" galaxies, usually associated with the kind of active star formation found in spiral galaxies.
Since nearby, contemporary clusters are dominated by elliptical "red" galaxies in which star-formation had long since ceased, Butcher and Oemler gave astronomers the first hint that the universe may once have contained far more spiral galaxies than it does now.
Using the wide-field/planetary camera--one of the Hubble's five imaging instruments--Dressler and his colleagues produced the photographs that they say prove that change.
This, he said, could indicate that spiral galaxies, with their eerie arms reaching out into space, evolve into elliptical galaxies. Ironically, that process is the exact opposite of an early postulation by Edwin P. Hubble, the venerated Nobel laureate from Caltech after whom the space telescope is named.
But the observation also could indicate something completely different, Dressler added. It could, for example, be evidence that spiral galaxies are chewed up or otherwise changed by collisions with other galaxies, a frequent occurrence in that relatively crowded section of the universe. Yet another possibility is that many spirals have merged in a tumultuous process that results in spherical, elliptical galaxies. This theory was advanced by Alar Toomre of the Massachusetts Institute of Technology and Francois Schweizer of the Carnegie Institution.