Cartwheel Galaxy
A lenticular ring galaxy shaped by a bullseye collision.
The Cartwheel Galaxy (catalogue ESO 350-40 and PGC 2248) is a lenticular ring galaxy approximately 500 million light-years away in the constellation Sculptor. Discovered by Fritz Zwicky in 1941, it is noted for its highly complicated structure, which Zwicky described as one of the most complex awaiting explanation based on stellar dynamics. Its D25 isophotal diameter of 57.69 kpc makes it slightly larger than the Andromeda Galaxy.
Quick Facts
- Constellation
- Sculptor
Facts from the source article.
Structures
The Cartwheel Galaxy’s structure is complex and severely disrupted. It features two rings: an outer ring, where gas and dust compression fuels intense star formation, and an inner ring encircling the core. A dark dust ring sits within the inner ring. Optical spokes link the outer and inner rings. Non-thermal radio continuum and optical spokes both exist, but they do not coincide.
Evolution
The galaxy was originally a normal spiral galaxy before a head-on bullseye collision with a smaller companion about 200–300 million years ago. The collision sent a powerful gravitational shock wave through the galaxy, sweeping up and compressing gas and dust and creating a starburst region around the unscathed center as it expanded outward. This produced the bluish ring around the center. The galaxy is beginning to regain a normal spiral form, with arms spreading from the core, often called spokes. An alternative model based on gravitational Jeans instability of axisymmetric and nonaxisymmetric perturbations does not appear to apply based on observational data. A fourth physically associated companion, G3, is linked to the group by a neutral hydrogen tail connecting it to the Cartwheel. Due to this tail and the structure's estimated age of about 300 million years, G3 is widely believed to be the intruding galaxy that plunged through the Cartwheel's disk, not G1 or G2. G3 lies roughly 88 kpc (about 287,000 light-years) away.
X-ray sources
The Cartwheel Galaxy's unusual shape may result from a collision with a smaller galaxy. Starburst activity produces large, luminous stars; when these explode as supernovae, they leave neutron stars and black holes. Some of these black holes have companion stars and become powerful X-ray sources as they pull matter from them, appearing as white dots along the rim of the X-ray image. The Cartwheel contains an exceptionally large number of such black hole binary X-ray sources due to the many massive stars formed in the ring.
More in Elliptical and Lenticular Galaxies
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced