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The Andromeda galaxy, also known as Messier 31 (M31), is the closest spiral galaxy to the Milky Way at a distance of about 2.5 million light-years. Astronomers use Andromeda to understand the structure and evolution of our own spiral, which is much harder to do since Earth is embedded inside the Milky Way.

The galaxy M31 has played an important role in many aspects of astrophysics, but particularly in the discovery of dark matter. In the 1960s, astronomer Vera Rubin and her colleagues studied M31 and determined that there was some unseen matter in the galaxy that was affecting how the galaxy and its spiral arms rotated. This unknown material was named "dark matter." Its nature remains one of the biggest open questions in astrophysics today, one that NASA's upcoming Nancy Grace Roman Space Telescope is designed to help answer.

This new composite image contains data of M31 taken by some of the world's most powerful telescopes in different kinds of light. The image above includes X-rays from NASA's Chandra X-ray Observatory and ESA's (European Space Agency's) XMM-Newton (represented in red, green, and blue); ultraviolet data from NASA's retired GALEX (blue); optical data from astrophotographers using ground-based telescopes (Jakob Sahner and Tarun Kottary); infrared data from NASA's retired Spitzer Space Telescope, the Infrared Astronomy Satellite, COBE, Planck, and Herschel (red, orange, and purple); and radio data from the Westerbork Synthesis Radio Telescope (red-orange).

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Each type of light reveals new information about this close galactic relative to the Milky Way. For example, Chandra's X-rays reveal the high-energy radiation around the supermassive black hole at the center of M31 as well as many other smaller compact and dense objects strewn across the galaxy. A recent paper about Chandra observations of M31 discusses the amount of X-rays produced by the supermassive black hole in the center of the galaxy over the last 15 years. One flare was observed in 2013, which appears to represent an amplification of the typical X-rays seen from the black hole.

These multi-wavelength datasets are also being released as a sonification, which includes the same wavelengths of data in the new composite. In the sonification, the layer from each telescope has been separated out and rotated so that they stack on top of each other horizontally, beginning with X-rays at the top and then moving through ultraviolet, optical, infrared, and radio at the bottom. As the scan moves from left to right in the sonification, each type of light is mapped to a different range of notes, from lower-energy radio waves up through the high energy of X-rays. Meanwhile, the brightness of each source controls volume, and the vertical location dictates the pitch.

This new image of M31 is released in tribute to the groundbreaking legacy of Dr. Vera Rubin, whose observations transformed our understanding of the universe. Rubin's meticulous measurements of Andromeda's rotation curve provided some of the earliest and most convincing evidence that galaxies are embedded in massive halos of invisible material—what we now call dark matter.

Her work challenged long-held assumptions and catalyzed a new era of research into the composition and dynamics of the cosmos. In recognition of her profound scientific contributions, the United States Mint recently released a quarter in 2025 featuring Rubin as part of its American Women Quarters Program—making her the first astronomer honored in the series.