The Dusty Arcs of the Andromeda Galaxy
M31 dust

Credit: NASA/JPL-Caltech

Observation • May 9th, 2024 • ssc2024-02b


This newly-processed image of the Andromeda galaxy uses data from NASA’s now-retired Spitzer Space Telescope to reveal the complex patterns of dust found in our Milky Way galaxy’s nearest neighbor. It shows the glow of polycyclic aromatic hydrocarbons glowing at a wavelength of 8 microns.

Infrared light provides a powerful tool for studying how new generations of stars are being formed in galaxies like Andromeda. Dust clouds in visible light are only seen as they block the light of background stars, but light up at longer infrared wavelengths.

The dust clouds in Andromeda form a ring running through the pancake-like disk of stars, along which we can see many areas in which new stars are being formed. However, arcs of dust found near the center of the galaxy provide a hint of the supermassive black hole that lies here.

To better isolate the dust features, especially towards the center of galaxy, the small contribution from starlight at 8 microns was removed by subtracting out carefully-scaled data at 4.5 microns, which is mostly dominated by the glow of stars. This provides better contrast to the arcs of dust found in the center of the Andromeda galaxy.

About the Object

Andromeda GalaxyM31Messier 31
Galaxy > Type > Spiral
2,500,000 Light Years

Color Mapping

Band Wavelength Telescope
Infrared 8.0 µm Spitzer IRAC


Position ()
RA =0h 42m 44.3s
Dec = 41° 16' 8.5"
Field of View
3.9 x 1.7 degrees
North is 49.8° left of vertical