At about 48,000 light-years across, the Hubble Space Telescope’s new photo of the Andromeda Galaxy (M31) is the largest, sharpest yet. It was revealed at the 225th meeting of the American Astronomical Society, which took play January 4th-8th 2015. In a news release, it was announced that the picture, which “represents a new benchmark for precision studies of large spiral galaxies that dominate the universe’s population of over 100 billion galaxies,” would be unveiled at the meeting in Washington state.
A total of 7,398 images were taken by the telescope, which had to be repositioned 411 times. This was done as part of the Panchromatic Hubble Andromeda Treasury (PHAT) program, Hubble’s “Multi-cycle program to map roughly a third of M31’s star forming disk, using 6 filters covering from the ultraviolet through the near infrared.” Using the telescope’s camera, specifically its Advanced Camera for Surveys and the Wide Field Camera 3, the galaxy was viewed in visible, and near-infrared wavelengths. The image revealed is a cropped version, spanning 1.5 billion-pixels. It is in natural visible-light color and was taken using the red and blue filters on the Advanced Camera. A wider view of the Andromeda Galaxy was also released, illustrating the extent of the PHAT program’s work. It was from this images that the photo was cropped.
Over 100 million stars are captured in the smaller composite image. Looking at the panoramic view, you can see “large groups of young blue stars indicate the locations of star clusters and star-forming regions…The dark silhouettes trace out complex dust structures. Underlying the entire galaxy is a smooth distribution of cooler red stars that trace Andromeda’s evolution over billions of years.” All of it is approximately 2.5 million light-years from Earth, which is a small distance when compared to Hubble’s usual subjects which are billions of light-years away.
Viewers can zoom-in and around a large version of the photo on the Hubble Space Telescope’s website. The section stretches across 61,000-light-years and was captured over a three year period from July 2010 through October 2013. The total exposure time for the images was 394 hours (16.1 days). Each image was shot in monochromatic (grayscale) and hues (colors) were matched to each, which resulted in the blues and yellows of the dust lanes, stellar clusters, spiral galaxies and star forming regions that can be seen in the photo.