Astronomy Picture of the Day—20190130

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2019 January 30

The Long Gas Tail of Spiral Galaxy D100

Image Credit & Copyright: NASA, ESA, Hubble, Subaru Telescope, W. Cramer (Yale)et al., M. Yagi, J. DePasquale

Explanation:Why is there long red streak attached to this galaxy? The streak is made mostlyof glowing hydrogen that has been systematically stripped away as the galaxymoved through the ambient hot gas in a cluster of galaxies. Specifically, thegalaxy is spiral galaxy D100, and cluster is the Coma Cluster of galaxies. Thered path connects to the center of D100 because the outer gas, gravitationallyheld less strongly, has already been stripped away by ram pressure. Theextended gas tail is about 200,000 light-years long, contains about 400,000times the mass of our Sun, and stars are forming within it. Galaxy D99, visibleto D100's lower left, appears red because it glows primarily from the light ofold red stars -- young blue stars can no longer form because D99 has beenstripped of its star-forming gas. The featured false-color picture is adigitally enhanced composite of images from Earth-orbiting Hubble and theground-based Subaru telescope. Studying remarkable systems like this bolstersour understanding of how galaxies evolve in clusters.