The Hubble Space Telescope recently celebrated 20 years of using the Advanced Camera for Surveys (ACS), which was installed on Hubble in March 2002 and has become its most widely used camera.

The ACS wavelength range extends from ultraviolet, through the visible spectrum, and into the near infrared. The ACS is capable of mapping large areas of the sky in great detail, and after installation the ACS became Hubble’s most widely used instrument.

Hubble ACS
The light echo around the star V838 Monocerotis seen by the Hubble Space Telescope in November 2005.

125,000 photos and counting

During its 20 years aboard Hubble, the ACS captured 125,000 images. These observations have been the source of numerous discoveries, several of which are presented on the website of the European Space Agency (ESA).

Hubble ACS
Astronauts Andrew Feustel (left) and John Grunsfeld, both STS-125 mission specialists, participate in the mission’s third extravehicular activity (EVA) session as work continues to refurbish and modernize the Hubble Space Telescope. During the six-hour, 36-minute spacewalk, Grunsfeld and Feustel removed the corrective optics space telescope axial replacement and installed the new Cosmic Origins spectrograph in its place. They also completed work on replacing the Advanced Camera for Surveys electronics board and completed part 2 of the ACS repair, installing a new electronics box and cable.

“We knew the ACS would add so much discovery potential to the telescope, but I don’t think anyone really understood all that it could do,” said the former astronaut – and one of two who have installed the ACS on Hubble – Mike Massimino. “It was going to reveal the secrets of the Universe.”

The ACS camera

ESA explains that the ACS is made up of three sub-instruments: the Wide Field Channel, the High Resolution Channel and the Solar Blind Channel. The Wide Field Channel is a high-performance, wide-field, optical, near-infrared camera designed to search for galaxies and galaxy clusters, explains the ESA.

Hubble ACS
The Advanced Camera for Surveys (ACS) aboard the NASA/ESA Hubble Space Telescope has used a natural “zoom lens” in space to improve its view of the distant universe. As well as offering an unprecedented and dramatic new view of the cosmos, the results promise to shed light on the evolution of galaxies and dark matter in space. Hubble has been peering into the center of one of the most massive galaxy clusters known, called Abell 1689. For this observation, Hubble had to stare at the distant cluster, located 2.2 billion light-years away, for more than 13 hours. The gravity of the trillions of stars in the cluster “plus dark matter” acts as a 2 million light-year-wide “lens” into space. This “gravitational lens” distorts and amplifies the light from galaxies far behind it, distorting their shapes and creating multiple images of individual galaxies.

The high-resolution channel was designed to take detailed pictures of the light from galaxies that featured massive black holes. This particular mode is currently not operational. Finally, the solar blind channel blocks visible light to allow weak ultraviolet radiation to be seen. This channel can be used to study weather patterns on other planets; for example, the auroras on Jupiter.

Hubble ACS
A colliding galaxy dubbed the “Tadpole” (catalog name UGC10214) is set against a rich tapestry of 6,000 galaxies. The tadpole, with its long tail of stars, looks like pinwheel fireworks, unlike conventional images of majestic spiral galaxies. Its distorted shape was caused by a small intruder, a very blue compact galaxy visible near the more massive tadpole. The tadpole resides about 420 million light-years away in the constellation Draco. Seen shining through the Tadpole Disk, the tiny intruder is likely a runaway galaxy now leaving the scene of the crash. Strong gravitational forces from the interaction created the long tail of debris, made up of stars and gas that spans more than 280,000 light-years.

ESA says that among its many accomplishments, the ACS helps map the distribution of dark matter, detects the most distant objects in the Universe, searches for massive exoplanets and studies the evolution of galaxy clusters.

“Two decades into its mission, the ACS continues to deliver groundbreaking science and some of the most incredible images of the distant Universe, and everything in between,” said Dan Coe, an astronomer from ESA/AURA who was part of the ACS team as an instrument scientist, says. “Looking back through the ACS image archive reminds us of the great diversity of galaxies, colors and stories that have been shared with the world.”

Header image caption: This collection of images features those taken by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), which celebrates 20 years of operation in March 2022.

Picture credits: NASA, ESA


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