Astronomers just got a new camera, and today they're proudly showing off their first images. Holland Ford of Johns Hopkins University has every reason to be proud: His 16-million-pixel Advanced Camera for Surveys (ACS), on board the Hubble Space Telescope, has snapped the deepest views of the universe ever. "When we saw the first images, my colleagues and I were stunned," says Ford, principal investigator on the project. "We had underestimated how good the camera would be."
ACS was mounted in Hubble's instrument bay by spacewalking astronauts during a weeklong servicing mission in March. During the same mission, astronauts repaired an infrared camera called NICMOS. The smallest details visible in the ACS images are about a tenth of an arc second wide--comparable to a grain of salt seen at a distance of 0.8 kilometer. ACS also has a much higher sensitivity and a larger field of view than Hubble's previous camera (Science, 22 February).
Ford presented the first four pictures from ACS at a press conference at NASA's headquarters in Washington, D.C. He lamented that the exquisite details of the images cannot be captured on television or in newspapers. "To see all of the detail, you need an 8-by-8-foot color print," he said. The most striking ACS image is a photo of a pair of merging galaxies called the Tadpole because of its long tidal tail of hot, blue stars. The Tadpole is 420 million light-years away--200 times farther than the Andromeda galaxy, the Milky Way's nearest neighbor. Nevertheless, individual stars can be seen in the galaxy. What's more, countless extremely faint and distant galaxies are visible in the background. According to Ford, twice as many background galaxies are present as in the previous camera's image, even though the ACS exposure time was 12 times shorter.
Within a couple of weeks, astronomers will start using ACS for their scientific programs, focusing mainly on the very early and distant universe. Meanwhile, says Dave Leckrone of NASA's Goddard Space Flight Center, "we'll do our best to have the first [infrared] images by NICMOS available early in June."