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Hubble sees further than ever before

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December 15, 2009

This image, taken in August 2009 by the WFC3 camera on the Hubble telescope, shows the old...

This image, taken in August 2009 by the WFC3 camera on the Hubble telescope, shows the oldest galaxies ever seen (photo: NASA)

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NASA's recently upgraded Hubble Space Telescope has made the deepest near-infrared image of the universe ever taken. Taken using a newly installed camera, the image shows deep space objects such as galaxies that formed only 600 million years after the Big Bang, making them the oldest galaxies ever seen. The image was taken with the Hubble’s new Wide Field Camera 3, which astronauts installed in May.

The image was taken in the same region of space as the Hubble Ultra Deep Field (HUDF) image, which was taken in 2004 and is the deepest visible-light image of the universe. Hubble's newly installed Wide Field Camera 3 (WFC3) collects light from near-infrared wavelengths and therefore can peer even deeper into the universe. This is because the light from very distant galaxies is stretched out of the ultraviolet and visible regions of the spectrum into near-infrared wavelengths by the expansion of the universe.

The WFC3 image, taken in late August 2009, definitely qualifies as a long exposure. The image was taken over the course of a total of four days of “pointing”, with 173,000 seconds of total exposure time. The image is a composite of three separate exposures each using one of three filters to sample a broad range of near-infrared wavelengths.

Infrared light is invisible to the human eye and so in the processed image from the WFC3, visible colors are assigned to each of the monochromatic images from the near-IR filter passes. The color results from assigning different hues to each monochromatic image. In this case, the assigned colors are blue for 1.05 micron wavelengths, green for 1.25 micron wavelengths, and red for 1.6 microns wavelengths. The representation is considered “natural” in that near-IR “blue” objects look blue and near-IR “red” objects look red.

The brightness in the image is also adjusted; the faintest objects are about one-billionth as bright as can be seen with the naked eye. The faintest and reddest objects in the image are galaxies that formed 600 million years after the Big Bang. No galaxies have ever been seen before from such early times.

The WFC3 is actually built from the Hubble Space Telescope’s original Wide Field and Planetary Camera and its filter assembly. These were brought back from Hubble when the Wide Field and Planetary Camera 2 was swapped in by astronauts in December 1993. For nearly 16 years, the camera responsible for many of the Hubble's most famous images was the Wide Field and Planetary Camera 2. That camera, also known as “the camera that saved Hubble”, was designed to correct for a nearly-mission-ending manufacturing flaw in Hubble’s main mirror. The flaw had caused blurry images since the space telescope was originally launched in 1990. In May 2009, astronauts replaced the WFPC2 with the new, US$132million WFC3. The old camera was brought back to Earth and will be sent to the Smithsonian.

The new camera is designed to be a versatile enough to image astronomical targets over a wide wavelength range. WFC3 was originally conceived with an optical channel only; the near-IR channel was added later. The instrument features an optical channel that uses a pair of 2048x4096 pixel charge-coupled devices (CCDs) to record images from 200 to 1000nm; and a separate infrared 1024×1024 pixel CCD that covers the wavelength range from 800 to 1700nm. The WFC3 is capable of the wide-field, low-resolution spectroscopy that astronomers use for surveys.

The WFC3 has a field of view comparable to the WFPC 2 that it replaces. The WFC3 also has a much larger field of view than the Near Infrared Camera and Multi-Object Spectrometer, which the WFC3 is largely designed to replace. WFC3 is intended to ensure that Hubble retains a powerful imaging capability through to the end of its lifetime.

This may be the last hurrah for the Hubble. The installation of the WFC3 back in May was likely the last service mission to the Hubble telescope. The previous service mission had been seven years earlier, although service is required every three years to keep Hubble running optimally. Hubble will probably end its mission, one way or another, by 2015. NASA is planning to launch the Hubble's successor, the James Webb Space Telescope (JWST) sometime in 2014.

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