Cartwheel Galaxy

At a glance

Key points

• Formed by a head-on galaxy collision
• Its outer ring is a wave of star birth
• Webb revealed dusty spokes

Two rings

The outer ring is an expanding wave of star birth and supernovae. Webb's mid-infrared view revealed hydrocarbon-rich dust spokes linking it to the bright inner ring.

How it was found

Fritz Zwicky picked out the Cartwheel on Palomar photographic plates in 1941. Ring galaxies like it are rare because they need a near bullseye: a smaller galaxy has to plunge almost straight through the centre of a disc. Before that impact the Cartwheel was probably an ordinary spiral much like the Milky Way, and its star-forming rim is now wider than our whole galaxy.

Seen across the spectrum

A 2006 composite from GALEX, Hubble, Spitzer and Chandra showed the outer ring bright in ultraviolet light from newborn stars 5 to 20 times the Sun's mass. Chandra found an exceptionally large number of X-ray sources along the rim, most likely black holes pulling gas from massive companion stars, which form readily where star birth is this intense. Hubble images from 2018 first hinted at the dusty spokes; Webb's 2022 NIRCam and MIRI images made them obvious and showed hot dust and giant young star clusters in the inner ring.

A passing phase

The rings are not permanent. They spread outward like ripples on a pond, and NASA describes the galaxy as in a very transitory stage that will keep changing. The Cartwheel lies in the southern constellation Sculptor and is far too faint for small telescopes; its detail is the work of large observatories and space telescopes.

What we still don't know

Which of the nearby small galaxies made the hit, and exactly when. Older studies put the impact roughly 100 million years ago, the Chandra team says several hundred million years, and Webb-era releases describe an outer ring that has been expanding for about 440 million years.

Missions

1. 1990–

   Hubble Space Telescope

   NASA / ESAActive

   Ultraviolet to near-infrared imaging from low Earth orbit.

   Mission page (opens in a new tab)

2. 2021–

   James Webb Space Telescope

   NASA / ESA / CSAActive

   Infrared observatory at Sun–Earth L2, about 1.5 million km from Earth.

   Mission page (opens in a new tab)

Related entries

• Stephan's QuintetFour interacting galaxies and an interloper
• Antennae GalaxiesTwo spirals merging

Sources

1. NASA Spitzer sig06-005: Cartwheel galaxy makes waves (opens in a new tab)
2. NASA Chandra (2006): Cartwheel galaxy (opens in a new tab)
3. Wolter 2024, Chandra symposium talk on the Cartwheel (Zwicky 1941) (opens in a new tab)
4. NASA Science: Webb: stellar gymnastics in the Cartwheel (opens in a new tab)
5. ESA: ESA/Webb weic2211a (opens in a new tab)

Last reviewed 10 Oct 2026 against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.