A recently discovered breed of galaxies really caught astronomers’ attention. Because they look like jellyfish.
 
Astronomers found the first jellyfish galaxy a decade ago. Such a galaxy has a disk of stars, like our Milky Way—plus long blue tendrils. A jellyfish galaxy was once a spiral like the Milky Way, spawning new stars from its gas and dust. But unlike the Milky Way, a jellyfish belongs to a cluster of galaxies.
 
A recent analysis of Hubble telescope images led to the conclusion that extremely hot gas from the cluster is behind the formation of jellyfish. That study is in the Astrophysical Journal Letters. [H. Ebeling, L. N. Stephenson, and A. C. Edge, Jellyfish: Evidence of extreme ram-pressure stripping in massive galaxy clusters]

As the galaxy plows through space, this hot gas rips out the galaxy's own gas and dust, forming the long streamers behind the galaxy. This torn-out gas still gives birth to new stars. The brightest of these newborn stars shine blue. So the former disc-shaped galaxy metamorphosizes into a celestial jellyfish sporting long blue tendrils.
 
The galaxy will eventually literally run out of gas, and thus lose the ability to create any more new stars. Jellyfish in the sea can be deadly. But in space, the mortally wounded victim is the jellyfish galaxy itself.

—written by Ken Croswell, voiced by Steve Mirsky

[The above text is a transcript of this podcast.]