Within the years following the launch of NASA’s Hubble Area Telescope, astronomers have tallied over 1 trillion galaxies within the universe. However just one galaxy stands out as crucial close by stellar island to our Milky Manner — the magnificent Andromeda galaxy (Messier 31). It may be seen with the bare eye on a really clear autumn night time as a faint cigar-shaped object roughly the obvious angular diameter of our Moon.
A century in the past, Edwin Hubble first established that this so-called “spiral nebula” was really very far outdoors our personal Milky Manner galaxy —at a distance of roughly 2.5 million light-years or roughly 25 Milky Manner diameters. Previous to that, astronomers had lengthy thought that the Milky approach encompassed all the universe. In a single day, Hubble’s discovery turned cosmology the wrong way up by unveiling an infinitely grander universe.
Now, a century later, the house telescope named for Hubble has achieved probably the most complete survey of this attractive empire of stars. The Hubble telescope is yielding new clues to the evolutionary historical past of Andromeda, and it seems to be markedly totally different from the Milky Manner’s historical past.
With out Andromeda as a proxy for spiral galaxies within the universe at massive, astronomers would know a lot much less in regards to the construction and evolution of our personal Milky Manner. That’s as a result of we’re embedded contained in the Milky Manner. That is like attempting to know the format of New York Metropolis by standing in the midst of Central Park.
“With Hubble we are able to get into huge element about what’s occurring on a holistic scale throughout all the disk of the galaxy. You’ll be able to’t do this with another massive galaxy,” stated principal investigator Ben Williams of the College of Washington. Hubble’s sharp imaging capabilities can resolve greater than 200 million stars within the Andromeda galaxy, detecting solely stars brighter than our Solar. They appear to be grains of sand throughout the seaside. However that’s simply the tip of the iceberg. Andromeda’s whole inhabitants is estimated to be 1 trillion stars, with many much less huge stars falling beneath Hubble’s sensitivity restrict.
Photographing Andromeda was a herculean process as a result of the galaxy is a a lot larger goal on the sky than the galaxies Hubble routinely observes, which are sometimes billions of light-years away. The total mosaic was carried out underneath two Hubble applications. In whole it required over 1,000 Hubble orbits, spanning greater than a decade.
This panorama began with the Panchromatic Hubble Andromeda Treasury (PHAT) program a couple of decade in the past. Pictures had been obtained at near-ultraviolet, seen, and near-infrared wavelengths utilizing the Superior Digital camera for Surveys and the Huge Subject Digital camera 3 aboard Hubble to {photograph} the northern half of Andromeda.
This program was adopted up by the Panchromatic Hubble Andromeda Southern Treasury (PHAST), lately revealed in The Astrophysical Journal and led by Zhuo Chen on the College of Washington, which added pictures of roughly 100 million stars within the southern half of Andromeda. This area is structurally distinctive and extra delicate to the galaxy’s merger historical past than the northern disk mapped by the PHAT survey.
The mixed applications collectively cowl all the disk of Andromeda, which is seen virtually edge-on — tilted by 77 levels relative to Earth’s view. The galaxy is so massive that the mosaic is assembled from roughly 600 separate fields of view. The mosaic picture is made up of not less than 2.5 billion pixels.
The complementary Hubble survey applications present details about the age, heavy-element abundance and stellar plenty inside Andromeda. It will enable astronomers to tell apart between competing situations the place Andromeda merged with a number of galaxies. Hubble’s detailed measurements constrain fashions of Andromeda’s merger historical past and disk evolution.
