NASA’s Hubble Space Telescope has captured an extraordinary mosaic image of the Andromeda galaxy, also known as Messier 31, offering unprecedented detail into its structure and history. The photomosaic, the largest of its kind, spans a width equivalent to six times the apparent diameter of the Moon. The galaxy, located 2.5 million light-years from Earth, is tilted nearly edge-on and appears as a vast oval. The intricate image reveals over 200 million stars, colourful regions and dark, filamentary clouds wrapping the galaxy’s disk.

According to the Panchromatic Hubble Andromeda Treasury (PHAT)

The northern half of the galaxy was mapped over a decade through ultraviolet, visible and infrared wavelengths. Published in The Astrophysical Journal, the subsequent Panchromatic Hubble Andromeda Southern Treasury (PHAST) expanded this work to the southern half. Led by Zhuo Chen of the University of Washington, this research focused on structural differences and the galaxy’s merger history, adding observations of approximately 100 million stars.

A Unique Evolutionary Path

Reports indicate that Andromeda’s history is markedly different from the Milky Way’s, despite both galaxies forming around the same time. As reported in an official press release by NASA, Ben Williams, principal investigator at the University of Washington, stated that Andromeda’s active history includes mergers with smaller galaxies, resulting in young star clusters and coherent streams of stars. The compact satellite galaxy Messier 32 is considered a remnant of past interactions.

Future Implications

The data from these observations are expected to inform future studies by NASA’s James Webb Space Telescope and the upcoming Nancy Grace Roman Space Telescope. Daniel Weisz from the University of California, Berkeley, noted Andromeda’s transition from a star-forming spiral galaxy to a system with a dominant bulge of older stars. Hubble’s findings will continue to shape our understanding of galactic evolution for decades to come, reports suggest.