In January 2015, NASA released the largest image ever of the Andromeda galaxy, called the Panchromatic Hubble Andromeda Treasury (PHAT), taken by the Hubble telescope. This composite image involved thousands of observations, hundreds of fields, spanned about a third of the galaxy and resolved over 100 million stars.
Totaling 1.5 billion pixels and requiring 4.3 gigabytes of disk space, this photo provides a detailed glimpse at the sheer scale of our nearest galactic neighbor.
Using this gigantic image, filmmaker Dave Achtemichuk created an unforgettable interactive experience.
To better understand what stars compose the Andromeda galaxy, a group of researchers studied the nearby spiral by composing the largest image ever taken with the Hubble Space Telescope. The result, called the Panchromatic Hubble Andromeda Treasury (PHAT), involved thousands of observations, hundreds of fields, spanned about a third of the galaxy, and resolved over 100 million stars. In the featured composite image below, the central part of the galaxy is seen on the far left, while a blue spiral arm is prominent on the right.
The brightest stars, scattered over the frame, are actually Milky Way foreground stars. The PHAT data is being analyzed to better understand where and how stars have formed in M31 in contrast to our Milky Way Galaxy and to identify and characterize Andromeda’s stellar clusters and obscuring dust.
Though the Andromeda galaxy is 2.5 million light-years from Earth, it is our galactic next-door neighbor on the universal scale. The Hubble Space Telescope is powerful enough to resolve individual stars in a 61,000-light-year-long stretch of the galaxy’s pancake-shaped disk. It’s like photographing a beach and resolving individual grains of sand. And there are lots of stars in this sweeping view — over 100 million, with some of them in thousands of star clusters seen embedded in the disk.
This ambitious photographic cartography of the Andromeda galaxy represents a new benchmark for precision studies of large spiral galaxies that dominate the universe’s population of over 100 billion galaxies. Never before have astronomers been able to see individual stars inside an external spiral galaxy over such a large contiguous area. Most of the stars in the universe live inside such majestic star cities, and this is the first data that reveal populations of stars in context to their home galaxy.
Hubble traces densely packed stars extending from the innermost hub of the galaxy seen at the left. Moving out from this central galactic bulge, the panorama sweeps from the galaxy’s central bulge across lanes of stars and dust to the sparser outer disk. Large groups of young blue stars indicate the locations of star clusters and star-forming regions. The stars bunch up in the blue ring-like feature toward the right side of the image. 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.
Because the galaxy is only 2.5 million light-years from Earth, it is a much bigger target in the sky than the myriad galaxies Hubble routinely photographs that are billions of light-years away. This means that the Hubble survey is assembled together into a mosaic image using 7,398 exposures taken over 411 individual pointings.