Seeing this picture, we are easily attracted by the spiral arms of the central spiral galaxy NGC 4654 in the constellation Virgo. This galaxy has a bright center and is called an "intermediate" galaxy because it has characteristics of both a barless spiral and a barred spiral. NGC 4654 lies north of the celestial equator, so it is visible from much of the Northern and Southern Hemispheres. The galaxy is approximately 55 million light-years away from Earth.
A spectacular image of the central spiral galaxy NGC 4654 captured by the Hubble Space Telescope in visible, ultraviolet and infrared light. Image credit: NASA Hubble Space Telescope, ESA, and J. Lee (Space Telescope Science Institute); Image processing: Gladys Kober (NASA): Gladys Kober (NASA/Catholic University of America)
NGC 4654 is one of many galaxies in the Virgo Cluster with an asymmetric distribution of stars and neutral hydrogen gas. Astronomers theorize that NGC 4654 may be undergoing a process called "ramstripping," in which the Virgo Cluster's gravity exerts pressure on NGC 4654 as it passes through an ultra-hot plasma composed mostly of hydrogen gas, known as the "intra-cluster medium." This pressure acts like a gust of wind—think of the wind a cyclist feels on a still day—carrying NGC 4654's gas away. This process creates a thin, long tail of hydrogen gas on the southeastern side of the galaxy. Most galaxies that have experienced ram stripping have very little cold gas, which prevents the galaxies from forming new stars because stars are produced from dense gas. However, NGC 4654's star formation rate is consistent with other galaxies of the same size.
About 500 million years ago, NGC 4654 also interacted with the companion galaxy NGC 4639. The gravity of NGC 4639 takes away the gas at the edge of NGC 4654, limiting the formation of stars in this area, resulting in an asymmetric star distribution in the galaxy.
Scientists study galaxies like NGC 4654 to study the connection between young stars and the cold gas that formed them. NASA's Hubble Space Telescope captured the image in visible, ultraviolet and infrared light.