The Tadpole galaxy

Holland Ford, the Johns Hopkins astronomer, has been waiting seven years to see the first pictures from the Advanced Camera for Surveys, whose development he led.

Ford could not have been more pleased.

"When we saw the first ACS images, my colleagues and I were stunned," he said. "We knew the ACS would be good, but we had underestimated how extraordinary the images would be."

The photograph that most illustrates the new capabilities is of the Tadpole galaxy, which has been altered by a collision with a smaller galaxy.

The tail of the Tadpole, officially called UGC 10214, was created by a very blue, compact galaxy visible in the upper left corner of the more massive Tadpole, which is about 420 million light-years away. Strong gravitational forces from the interaction created the long tail of debris, consisting of stars, gas and dust that stretch out more than 280,000 light-years.

Previous ground-based images showed the overall structure but could not reveal individual stars.

Numerous young blue stars and star clusters, spawned by the galaxy collision, are seen in the spiral arms, as well as in the long "tidal" tail of stars. Each of these clusters represents the formation of up to about a million stars. Their color is blue because they contain very massive stars, which are 10 times hotter and 1 million times brighter than our Sun.

Once formed, the star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. These clusters will eventually become old globular clusters similar to those found in essentially all halos of galaxies, including our own Milky Way.

Two prominent clumps of young bright blue stars in the long tail are separated by a "gap" -- a section that is fainter than the rest of the tail. These clumps of stars will likely become dwarf galaxies that orbit in the Tadpole's halo.

ACS made this observation on April 1 and 9, 2002. The color image is constructed from three separate images taken in near-infrared, orange, and blue filters.

The image is more important for the roughly 6,000 galaxies that are visible in the background. Ford said the faintest of these galaxies, some seen as they were when the universe was less than 10 percent of its current age, can only be seen when the image is blown up into an 8-foot by 8-foot poster.

The picture prompted a bold claim:

"There is no doubt that the Advanced Camera will provide humanity with the deepest view of the universe that has ever been made," Ford said.

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