Galaxy Formation in 18 Easy Pieces...and Counting

Rogier Windhorst was an active radio astronomer when the flawed Hubble Space Telescope (HST) was put into Earth orbit in 1990. Working with ground-based radio telescopes such as the Westerbork Synthesis Radio Telescope in The Netherlands, the Very Large Array in New Mexico, the Palomar 200-inch telescope in California, and the Multiple Mirror Telescope on Arizona’s Mt. Hopkins, the ASU astronomer already had several galaxy discoveries under his belt.

When scientists heard that the HST was flawed, they became wary of using it. Hubble data was not in as high demand as had been expected. Windhorst took this opportunity to jump to the front of the line.

“I was sort of a guinea pig to see if you could do good science with a flawed telescope,” Windhorst says.

Windhorst did just that. He targeted a galaxy with a redshift of 2.4—11 billion light-years from Earth—and used the HST to study it at higher resolution. His experience with radio astronomy techniques came in handy, and allowed him to sharpen flawed images by using computer algorithms. Here he saw the first visible-light images of his galaxy, in blurred but bearable focus.

In 1994, Windhorst was offered the opportunity to take images with the repaired HST. With the corrected telescope, he could look even further out, where the light was older—deeper into the universe’s past. Using more filters to look at the same area as before, he made an unexpected discovery.

“That was a real boon, because we discovered something absolutely amazing,” Windhorst recalls. “I’d been studying this area of space since 1988. Now I was seeing 18 objects completely unknown to me.”

The discovery was difficult to explain at first. It remained difficult until Windhorst and his colleagues realized that looking through the Hubble was like looking through a long straw. The distance between the telescope and the objects it observes may be great, but the angular distance between the objects it observes remains the same. It is no greater than the distance between our Milky Way Galaxy and the Andromeda Galaxy—our nearest neighbor at a distance of a mere 2 million light years.

Once they realized the amount of space involved, Windhorst and his colleagues had their explanation. What they were seeing were the building blocks of galaxies.

“These pictures were showing us how galaxies form,” he explains. “They showed us that smaller clumps—sub-galactic clumps—merge over the course of time. They move around. Smaller ones get caught in the gravity of larger ones. The big guys gobble up the little ones. Kind of like corporate mergers on Wall Street.”

Since finding sub-galactic clumps at a redshift of 2.4, Windhorst has gone back and found even smaller pieces at redshift of 6. That is nearly 13 billion light-years from Earth. He has chased young and forming galaxies back to the edge of the observable universe—the end of what astronomers refer to as the “Dark Ages” of the universe.

But, like the young galaxies from Windhorst’s other work, these objects are just the beginning of what is sure to be a wealth of future discovery.

“If we could go another hundred or thousand times fainter, we would see perhaps tens of thousands of clumps that happened even earlier than the first 900 million years,” he says. “We might see light from 500 million or 300 million years after the Big Bang. And that would be like observing the very first stars, or seeing the beginning of the end of the ‘Dark Ages.’”

To see these objects, the ASU astronomer says that much more sensitive detectors are necessary. For this reason, Windhorst is involved in planning NASA’s “Next Generation Space Telescope,” the James Webb Space Telescope (JWST).

The JWST will be physically larger than the Hubble. It will have a deployable mirror 6.5 meters in diameter that is made of hexagonal segments. NASA plans to place the JWST far out in a point past the orbit of our moon. This will get it away from the “background noise” of the Earth. Currently scheduled for launch in 2011, the JWST will also be fine-tuned to do infrared observations work. Scientists will use it to search for the earliest stars of the universe.

“If there is first light out there, this telescope will see it,” Windhorst says. “We will then know how the first stars started shining.”—Matthew Shindell