Hubble Comes Face-to-Face with Spiral’s Arms

Andrea Gianopoulos

May 9, 2025

A spiral galaxy viewed face-on, with a slightly oval-shaped disk. The galaxy’s center appears as a bright white spot surrounded by a golden glow. Two spiral arms extend out from the center, wrapping around the galaxy and broadening out to form the thick outer edge of the disk. Thin reddish strands of dust and bright pink spots follow the arms through the disk. Faint strands of stars extend from the tips of the spiral arms and out beyond the disk.

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Hubble Comes Face-to-Face with Spiral’s Arms

This Hubble Space Telescope image showcases the spiral galaxy NGC 3596.ESA/Hubble & NASA, D. Thilker

The spiral galaxy NGC 3596 is on display in this NASA/ESA Hubble Space Telescope image that incorporates six different wavelengths of light. NGC 3596 is situated 90 million light-years from Earth in the constellation Leo, the Lion. British astronomer Sir William Herschel first documented the galaxy in 1784.

NGC 3596 appears almost perfectly face-on when viewed from Earth, showcasing the galaxy’s neatly wound spiral arms. These bright arms hold concentrations of stars, gas, and dust that mark the area where star formation is most active, illustrated by the brilliant pink star-forming regions and young blue stars tracing NGC 3596’s arms.

What causes these spiral arms to form? It’s a surprisingly difficult question to answer, partly because spiral galaxies are so diverse. Some have clear spiral arms, while others have patchy, feathery arms. Some have prominent bars across their centers, while others have compact, circular nuclei. Some have close neighbors, while others are isolated.

Early ideas of how spiral arms formed stumped astronomers with the ‘winding problem’. If a galaxy’s spiral arms are coherent structures, its arms would wind tighter and tighter as the galaxy spins, until the arms are no longer visible. Now, researchers believe that spiral arms represent a pattern of high-density and low-density areas rather than a physical structure. As stars, gas, and dust orbit within a galaxy’s disk, they pass in and out of the spiral arms. Much like cars moving through a traffic jam, these materials slow down and bunch up as they enter a spiral arm, before emerging and continuing their journey through the galaxy.

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Media Contact:

Claire Andreoli (claire.andreoli@nasa.gov)NASA’s Goddard Space Flight Center, Greenbelt, MD