As the article mentions, this is most likely due to the rotation of the cluster. Throwing some numbers out there: The Virgo cluster is 60Mly away which is ~20M

As the article mentions, this is most likely due to the rotation of the cluster. Throwing some numbers out there: The Virgo cluster is 60Mly away which is ~20Mpc (mega parsecs). Hubble's law [1] (v = Hd) tells us that for every 1Mpc away an object is, the expansion of the universe causes it to move away from us at about 70 km/s. So 20Mpc -> 1400km/s. The true velocity is actually about 300km/s less than this because the local group is being pulled gravitationally towards Virgo. (If you are interested, this movement of the local group towards Virgo is the largest component of the earth's motion relative to the CMB. Some of the others being the earth's motion around the sun and the sun's around the milky way). The velocity dispersion of large clusters is known to be on the order of 1000 km/s, so its not surprising that one or two objects whose orbits happen to be bringing them towards us are net blueshifted. The long and the short of it is that this is more of a cool curiosity than evidence of something crazy going on. [1] https://en.wikipedia.org/wiki/Hubble%27s_law https://en.wikipedia.org/wiki/Hubble%27s_law