An image captured by the Hubble Space Telescope shows the Cartwheel Galaxy shows its particular structure that combines features of a lenticular galaxy and a ring galaxy. Its unusual shape is probably the result of a collision with another smaller galaxy that caused a series of shock waves in its nucleus that pushed gas and dust outwards. A long-term consequence of that accumulation of gas in the outer ring is the birth of a lot of massive stars, visible in blue.
The Cartwheel Galaxy, also known as LEDA 2248, ESO 350-40 or IRAS 00352-3359, is about 500 million light years from the Milky Way, has an estimated diameter of about 150,000 light years and a total mass estimated at about 3 billion solar masses. Probably until 600-700 million years ago it was a spiral galaxy like the Milky Way before the collision that altered its shape.
The nickname Cartwheel galaxy is due to the shape we currently see but the spiral structure is slowly starting to getting restored by the gravitational forces in action inside it. The consequence is that now from the Earth we can already see the new spiral’s arms that are forming between the new galaxy’s nucleus and its outer ring.
That ring is spectacular and interesting to study for the amount of massive stars that were born after the galaxy merger. Astronomers estimate that several billion massive stars formed in a time span that’s short from an astronomical point of view. This was only possible thanks to an abnormal accumulation of gas on the galaxy’s outer edge.
Those massive stars consume their hydrogen very quickly so they die after a few million years exploding into supernovae that leave neutron stars or black holes. They can have a normal star as their companion and steal gas from it that gets heated up a lot. The consequence is that in the Cartwheel Galaxy’s outer ring there are also many X-ray sources.
This new image of the Cartwheel Galaxy is based on archival data that were reprocessed using FITS Liberator 3, a free and open source software developed at the Space Telescope European Coordinating Facility (ST-ECF) to process graphic files in the FITS (Flexible Image Transport System) format. This allowed to bring out new details in old images like this one, allowing to better understand the evolution of this galaxy merger.