Hubble Glimpses Galactic Gas Making a Getaway
A sideways spiral galaxy shines in this NASA/ESA Hubble Space Telescope image. Located about 60 million light-years away in the constellation Virgo (the Maiden), NGC 4388 is a resident of the Virgo galaxy cluster. This enormous cluster of galaxies contains more than a thousand members and is the nearest large galaxy cluster to the Milky Way.
NGC 4388 appears to tilt at an extreme angle relative to our point of view, giving us a nearly edge-on prospect of the galaxy. This perspective reveals a curious feature that wasn’t visible in a previous Hubble image of this galaxy released in 2016: a plume of gas from the galaxy’s nucleus, here seen billowing out from the galaxy’s disk toward the lower-right corner of the image. But where did this outflow come from, and why does it glow?
The answer likely lies in the vast stretches of space that separate the galaxies of the Virgo cluster. Though the space between galaxies appears empty, this space is occupied by hot wisps of gas called the intracluster medium. As NGC 4388 moves within the Virgo cluster, it plunges through the intracluster medium. Pressure from hot intracluster gas whisks away gas from within NGC 4388’s disk, causing it to trail behind as NGC 4388 moves.
The source of the ionizing energy that causes this gas cloud to glow is more uncertain. Researchers suspect that some of the energy comes from the center of the galaxy, where a supermassive black hole spins gas around it into a superheated disk. The blazing radiation from this disk might ionize the gas closest to the galaxy, while shock waves might be responsible for ionizing filaments of gas farther out.
This image incorporates new data, including several additional wavelengths of light, that bring the ionized gas cloud into view. The image holds data from several observing programs that aim to illuminate galaxies with active black holes at their centers.
Image credit: ESA/Hubble & NASA, S. Veilleux, J. Wang, J. Greene