A photograph 10 years in the making and featuring 200 million stars is helping scientists better understand our Milky Way galaxy.
University of Washington astronomers have been studying the image of the Andromeda galaxy, 2.5 million light years away, created by the Hubble Space Telescope.
Principal investigator Benjamin Williams said the photo was a result of the telescope’s most comprehensive survey of the galaxy and yielded new clues to the evolutionary history of Andromeda.
Associate Professor Williams said without Andromeda as an example of a spiral galaxy, astronomers would know much less about the structure and evolution of our own Milky Way.
“That’s because Earth is embedded inside the Milky Way. This is like trying to understand the layout of New York City by standing in the middle of Central Park,” he said.
“With Hubble we can get into enormous detail about what’s happening on a holistic scale across the entire disk of the galaxy. You can’t do that with any other large galaxy.”
Associate Professor Williams said Hubble’s sharp imaging capabilities could resolve more than 200 million stars in the Andromeda galaxy, detecting only stars brighter than our sun.
He said they looked like grains of sand across the beach.
“But the telescope can’t capture everything. Andromeda’s total population is estimated to be 1 trillion stars, with many less massive stars falling below Hubble’s sensitivity limit.”
Associate Professor Williams said photographing Andromeda was a Herculean task because the galaxy was a much bigger target in the sky than the galaxies Hubble routinely observed, which were often billions of light years away.
“The full mosaic was carried out under two Hubble programs. In total it required over 1000 Hubble orbits, spanning more than a decade.”
Associate Professor Williams said the Hubble survey programs provided information about the age, heavy-element abundance and stellar masses inside Andromeda.
He said this would allow astronomers to distinguish between competing scenarios where Andromeda merged with one or more galaxies.
“Though the Milky Way and Andromeda galaxies formed presumably around the same time many billions of years ago, observational evidence shows that they have very different evolutionary histories, despite growing up in the same cosmological neighborhood.”
Associate Professor Williams said Andromeda seemed to be more highly populated with younger stars and unusual features like coherent streams of stars.
“This implies it has a more active recent star formation and interaction history than the Milky Way.”
Read the full study: PHAST. The Panchromatic Hubble Andromeda Southern Treasury. I. Ultraviolet and Optical Photometry of over 90 Million Stars in M31.
