Study of Andromeda by Vera Rubin enriched our knowledge of galaxies, led to discovery of dark matter and transformed understanding of the universe. To commemorate this, NASA has released several new images of Andromeda or M31 galaxy in tribute to her legacy.
Situated in the Local Group (LG) that contains over 80 galaxies, Andromeda galaxy (also known as Messier 31 or M 31) and our home galaxy Milky Way (MW) are large spiral galaxies separated by a distance of 2.5 million light-years. They are only spiral galaxies visible to the naked eye hence have been of special interest to the astronomers. Being embedded in the Milky Way makes it difficult to study it hence astronomers have depended on Andromeda also for studying structure and evolution of our home galaxy.
In the 1960s, astronomer Vera Rubin studied Andromeda and other galaxies. She observed that the stars at the outer edges of the galaxies were revolving with a speed as fast as the speeds of the stars towards the centre. In such situation, the galaxy should have flown apart for the given sum of all observed matter, however that is not the case. This meant there must be some additional invisible matter that keep the galaxies together and cause them to rotate at such high speeds. The invisible matter was termed “dark matter.” Vera Rubin’s measurements of rotation curves of Andromeda provided earliest evidence of dark matter and shaped the future course of physics.
Study of Andromeda by Vera Rubin enriched our knowledge of galaxies, led to discovery of dark matter and transformed understanding of the universe. To commemorate this, NASA has released several new images of Andromeda or M31 galaxy in tribute to Vera’s legacy. The composite image contains data of the galaxy taken by various telescopes in different types of light.
X-ray: NASA/CXO/UMass/Z. Li & Q.D. Wang, ESA/XMM-Newton; Infrared: NASA/JPL-Caltech/WISE, Spitzer, NASA/JPL-Caltech/K. Gordon (U. Az), ESA/Herschel, ESA/Planck, NASA/IRAS, NASA/COBE; Radio: NSF/GBT/WSRT/IRAM/C. Clark (STScI); Ultraviolet: NASA/JPL-Caltech/GALEX; Optical: Andromeda, Unexpected © Marcel Drechsler, Xavier Strottner, Yann Sainty & J. Sahner, T. Kottary. Composite image processing: L. Frattare, K. Arcand, J.Major
In various single spectrum images, Andromeda appears relatively flat, like all spiral galaxies viewed at this distance and angle. Its spiralling arms circle around a bright core, creating a disk shape. In each image, this close galactic relative to the Milky Way has a similar shape and orientation, but the colours and details are very different that reveal new information. In most of the images, the flat surface of the galaxy is tilted to face our upper left.
| Single-spectrum images | Features of M31 revealed | Data sources |
| X-rays | No spiral arms are present in the X-ray image. High-energy radiation seen around the supermassive black hole at the centre of M31 as well as many other smaller compact and dense objects strewn across the galaxy. | NASA’s Chandra and ESA’s XMM-Newton Space X-ray Observatories. (represented in red, green, and blue) |
| Ultraviolet (UV) | The spiralling arms appear icy blue and white, with a hazy white ball at the core. | NASA’s retired GALEX (blue) |
| Optical | Hazy and grey image, spiralling arms appear like faded smoke rings. The blackness of space is dotted with specks of light, and a small bright dot glows at the core of the galaxy. | Ground based telescopes (Jakob Sahner and Tarun Kottary) |
| Infrared (IR) | A white spiralling ring encircles a blue centre with a small golden core, the outer arms fiery. | NASA’s retired Spitzer Space Telescope, the Infrared Astronomy Satellite, COBE, Planck, and Herschel (red, orange, and purple) |
| Radio | The spiralling arms appear red and orange, like a burning, loosely coiled rope. The centre appears black, with no core discernible. | Westerbork Synthesis Radio Telescope (red-orange) |
In the composite image, the spiralling arms are the colour of red wine near the outer edges, and lavender near the centre. The core is large and bright, surrounded by a cluster of bright blue and green specks. Other small flecks in a variety of colours dot the galaxy, and the blackness of space surrounding it.
This collection helps astronomers understand the evolution of the Milky Way, the spiral galaxy we live in.
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Sources:
- NASA Image article – NASA’s Chandra Shares a New View of Our Galactic Neighbor. Posted 25 June 2025. Available at https://www.nasa.gov/image-article/nasas-chandra-shares-a-new-view-of-our-galactic-neighbor/
- Rubin Observatory. Who was Vera Rubin? Available at https://rubinobservatory.org/about/vera-rubin
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