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  Then There Was Light

This shot of the Swan Nebula, which astronomers believe is illuminated by hidden young stars, was among the first four images released by NASA from the Advanced Camera for Surveys (ACS).
Photo courtesy NASA, H. Ford, G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA

By Michael Purdy

When astronomers peer out from Earth into the vast recesses of the universe, they do much more than look across space. Light from galaxies and other distant objects must travel for millions or billions of years before it reaches Earth, so when astronomers observe those objects now, they're actually seeing the way they looked long ago.

The astronomers' trek across space and time towards the edge of the universe and its creation has been powerfully aided for a decade by the orbiting Hubble Space Telescope.

Before (at left) and after images reveal the eruption of a distant exploding star (highlighted with an arrow on the right). The right image was taken using ACS, which astronomers think will enable them to find many of these stars, known as supernovae.
Photo courtesy NASA and Blakeslee

In March 2002, astronomers' ability to peer across the universe entered a new phase when astronauts from the space shuttle Columbia installed the Advanced Camera for Surveys (ACS) in the orbiting Hubble telescope. Holland Ford, professor of physics and astronomy in the Krieger School of Arts and Sciences, led a team of scientists and engineers that spent five years designing and building the ACS, packing its frame — about the size of an old-fashioned phone booth — with the most powerful and technologically advanced observational equipment available.

Ford predicted in early 2002 that the ACS would increase Hubble's potential for discovery tenfold. Astronomers would be able to image more distant objects in shorter observing runs, at higher resolutions, and over wider swaths of sky than ever before.

Also among the first four ACS images released by NASA was this photo of the Cone Nebula, a structure of cold gas and dust. Astronomers are still unsure of this nebula's origins.
Photo courtesy NASA, H. Ford, G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA
Just over a month after the ACS installation, at an April 20, 2002, press conference, Ford and NASA offered the public four colorful and gorgeously detailed images of distant space produced by ACS.

Scientists don't generally admit to being tickled, but Ford is clearly delighted when he speaks of the results astronomers have obtained from ACS.

"It is very rare that Dr. Murphy — of Murphy's Law — takes a holiday, but in the case of our wide field camera, Dr. Murphy did indeed take a holiday," says Ford. "That camera's sensitivity was about 10 percent better than we thought it would be based on the calibrations we did on the ground. It nearly always goes the other direction. What a nice surprise!"

A Hopkins astronomer, Holland Ford, led the effort to design and build ACS, but teams from many places are now using ACS to produce remarkable new images. Right, scientists from NASA and the European Space Agency (ESA) used ACS to take their deepest look ever into faint stars in the halo surrounding the nearby Andromeda Galaxy.
Photo courtesy NASA, ESA and T.M. Brown (STScI)
ACS highlights include the discovery of the largest-ever instance of a phenomenon known as a gravity lens. Narciso Benítez, an ACS team member and an associate research scientist at Johns Hopkins, led the team that produced the image of the gravity lens, which occurs when the gravity of an enormous mass (in this case, a cluster of galaxies) warps and magnifies the light coming from behind it (see image by Narciso Benítez towards end of feature.).

"People who were working in [galaxy] clusters and gravitational lenses were astonished," says Benítez. "We had quite a few people say that it is one of the most beautiful pictures they had ever seen."

Astronomers from NASA, the National Optical Astronomy Observatory (NOAO), and the ESA produced this image of the Helix Nebula by combining nine images taken with the ACS and a wider image from a ground-based telescope.
Photo courtesy NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO)
More than just beautiful, the new image delivered insights into important astronomical phenomena like early galaxies and dark matter, adds Benítez.

Ford and John Blakeslee, an associate ACS research scientist at Johns Hopkins, made news in April when they announced the detection of two new and very distant supernovae. Through ACS, they were able to identify the supernovae as members of a class of exploding stars astronomers use to gauge distances across the universe (see opening image at the beginning of this feature).

"The sharper images, wider viewing area, and keener sensitivity of ACS should allow astronomers to discover roughly 10 times as many of these cosmic beacons as was possible with Hubble's previous main imaging camera," commented Blakeslee at the time. The new supernovae will help astronomers develop a picture of the universe's expansion, a process that is much more complicated than they originally expected.

Hopkins astronomer Narciso Benítez and others produced this ACS image by peering through a massive cluster of galaxies. The gravity of tremendous masses can bend light just like a lens, and in this case the cluster of galaxies has bent and magnified the images of galaxies behind the galactic cluster, giving astronomers a look at some of the most distant galaxies they've ever seen.
Photo courtesy NASA, N. Benitez, T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford, M. Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/LO), the ACS Science Team, and ESA
The astronomers who use ACS have only just started work on an ambitious agenda of groundbreaking new studies. Included in their objectives are probing the structure and evolution of the distant, early universe; looking for early signs of planetary formation; investigations of the geometry of the universe; and, if they're very lucky, maybe even the first direct images of planets in other solar systems. Ford, clearly tantalized by the last possibility, admits that it's a long shot.

"I think that there is a chance," he says. "It's going to be difficult, for sure, but we're going to try it."

The other two ACS images initially released by NASA included these shots of the Mice (top), two spiral galaxies colliding in a violent merger, and the Tadpole Galaxy (bottom), another galaxy involved in a violent collision.
Photo courtesy NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M. Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA

Whether that effort is successful or not, Ford is confident that a range of new discoveries and insights from ACS observations are on the way.

"In a lot of areas, observers who use the ACS simply will write the chapters in textbooks, and those chapters aren't going to be superseded for a decade or more until there is a telescope with an order of magnitude larger size than Hubble," says Ford.

NASA planners hope to launch the next space telescope in 2011. Hubble's schedule calls for it to be retired in 2010, but Ford and other astronomers have been urging NASA to consider an extension that will keep Hubble aloft longer, and an expert panel recently agreed with them. Regardless of whether that extension is won, ACS will stay in Hubble until its retirement.

(For a complete list of scientists and engineers from across the country who contributed to ACS, go to

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