The Hubble Space Telescope has given astronomers their first family album of galaxies as they appeared during the earliest stages of their evolution.
Some of the galaxies photographed have a family resemblance to those visible nearby today. But others, scientists say, are as weird and puzzling as some of the fossil creatures paleontologists have found in Earth's evolutionary past.
Hubble has made many discoveries, "but perhaps this is the most unexpected so far," said Dr. Duccio Macchetto of the Space Telescope Science Institute in Baltimore and the European Space Agency. "We are opening up a whole area of research we will have to pursue with every tool we have. It has certainly opened up more questions than we have been able to answer. And that's part of the fun."
Probing the universe's origins and the evolution of galaxies was one of the space telescope's top assignments. Thanks to its orbit above the Earth's obscuring atmosphere, and optical repairs made by Discovery astronauts a year ago, Hubble can now find and resolve distant objects that appear as mere blobs, if at all, to other observatories.
And because light from the most distant objects has been traveling toward Earth for the longest time, the information it carries reveals the objects as they appeared in the first few billion years after the Big Bang. The Big Bang is the cataclysmic event that scientists believe was the beginning of all matter, time and space.
The Hubble photographs, released this week at the Goddard Space Flight Center in Greenbelt, have captured images of galaxies in dense clusters as they appeared 2 billion, 5 billion and 9 billion years after the Big Bang. The dates assume the universe is now 14 billion years old, a figure still hotly debated.
One of the first surprises from the new family album is that spiral galaxies like our own Milky Way, which make up 20 percent to 30 percent of today's galactic population, appear to be missing in the earliest epoch, 2 billion years after the Big Bang. There are plenty of stable, football-shaped elliptical galaxies in all the epochs, and they are much like those that make up most of today's array. But at 2 billion years there are no spirals.
"One of the theories of galaxy formation is that if you have a merger of two spiral galaxies, we produce an elliptical galaxy," said Dr. Macchetto. "So it was natural to expect more spiral galaxies in the early epoch than there are today. But that's not what we find . . . so we have to do more work."
By 5 billion years after the Big Bang, he said, "we see more structure, but we don't -- and that is part of the puzzle -- we don't recognize much of the structure. . . . It really is a zoo of animals we don't know how to classify yet."
The menagerie appears to include shredded fragments of galaxies either forming or being torn apart. Baffled astronomers are describing them as "tadpoles," "train wrecks" and "demolition derbies."
"We have to come all the way to 9 billion years after the Big Bang before we get to a more recognizable universe," he said.
Some of the galaxies at that age have the appearance of spirals, said Dr. Mark Dickinson of the space telescope institute. But "they look a little sick."
In contrast with the mostly majestic spirals in nearby space and time, he said, those at 9 billion years after the Big Bang "seem to be getting roughed up a bit, so something about that environment is making it hard for those spirals to survive."
"The fact that we see so much more activity and strange shapes in very distant clusters, if nothing else, is proof that despite the relative stability of elliptical galaxies, there is a very dynamic process affecting spiral galaxies," he said.
It's possible, Dr. Dickinson said, that the dynamics of galactic evolution in the dense clusters of galaxies Hubble photographed are different from those in more "rural" regions of the universe.
"We do need to extend our research to other sorts of environments . . . to see whether these phenomena are universal or specifically related to cluster environments," Dr. Dickinson said.
Although few scientists today doubt that the universe formed billions of years ago and has been evolving and changing ever since, he said, "this is a nice demonstration of the kind of evolution you would expect."
It also reaffirms the power of the repaired Hubble Space Telescope to open new windows on the universe and its origins.
"I would say it's phenomenal," Dr. Dickinson said. "With each project I find my jaw dropping."