This Hubble image shows most of Messier 90, a spiral galaxy roughly 60 million light-year away in the constellation of Virgo. The galaxy is part of the Virgo Cluster, a group of over 1,200 galaxies bound together by gravity.
This image combines infrared, ultraviolet, and visible light gathered by Hubble’s Wide Field and Planetary Camera 2 that was operational between 1994 and 2010. That camera produed images with the staircase-like shape as seen here because it used four light detectors with overlapping fields of view. One of the detectors had a higher magnification than the other three. When the four images are combined together in one picture, the high-magnification image needs to be reduced in size in order for the image to align properly, resulting in an image with a layout that looks like steps.
Messier 90 is remarkable; it is one of the few galaxies seen to be traveling toward the Milky Way, not away from it. As the Universe expands, the galaxies are generally moving away from each other, and that motion causes their light to be shifted to longer wavelengths by the Doppler Effect. But sometimes, local gravity conditions can change the relative motion of galaxies, so it’s possible for individual galaxies to be moving toward us. One result of such motion is that their light appears shifted to shorter wavelengths—blueshift rather than redshift.
M90’s blueshift is likely caused by the Virgo Cluster’s colossal mass accelerating its members to high velocities, sending them on paths that take them both towards and away from us over time. While the cluster itself is moving away from us, some of its constituent galaxies, such as M90, are moving faster than the cluster as a whole. From Earth, we see the galaxy heading towards us.
Image Credit: NASA/ ESA