Two galaxies in the Virgo Cluster show themselves affected by ram pressure stripping in a set of Hubble Space Telescope images.
The spiral galaxy NGC 4522 – shown at the top of this post – is one of the galaxies. It is located in the Virgo cluster some 60 million light-years away from Earth. It is a spectacular example of a spiral galaxy currently being stripped of its gas content. The galaxy’s rapid motion within the Virgo cluster results in strong winds across the galaxy as the gas within is left behind.
Scientists estimate that NGC 4522 is moving at more than 10 million kilometers per hour. A number of star clusters that formed in the stripped gas can be seen in the Hubble image.
Even though this is a still image, Hubble’s view of NGC 4522 practically swirls off the page with apparent movement. It highlights the dramatic state of the galaxy, with an especially vivid view of the ghostly gas being forced out of it. Bright blue pockets of new star formation can be seen to the right and left of center. The image also shows distant background galaxies.
Another galaxy, NGC 4402 – shown at right – also displays some telltale signs of being stripped of its gas and dust. One sign is the curved, or convex, appearance of the galaxy’s disc. It’s thought this appearance is a result of the forces exerted by the intra-cluster medium, which is an extremely hot X-ray emitting gas found between galaxies within galactic clusters. Light shining from the galaxy’s disc backlights the swirling dust that is being swept out by the gas.
The process at work in these galaxies ram pressure stripping is the drag force that results when something moves through a fluid. It’s much like the wind you feel in your face when bicycling, even on a still day. For galaxies, it happens as they orbit around the center of the cluster, moving through the intra-cluster medium.
Ram pressure stripping happens when a galaxy moves through the intra-cluster medium. As it moves through this intra-cluster medium, strong winds rip through it, sweeping out gas and dust, distorting its shape, and even halting star formation. This interaction can result in peculiar-looking galaxies. Studying ram pressure stripping helps astronomers better understand the mechanisms that drive the evolution of galaxies, and how the rate of star formation is suppressed in very dense regions of the universe such as clusters.
Both images were taken by the Advanced Camera for Surveys on Hubble before it suffered from a power failure in 2007. Astronauts on Servicing Mission 4 in May 2009 were able to restore ACS during their 13-day mission.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.