The large gravity of the dark matter halo in this interpretation explains the perturbed nature of the nearby spiral galaxy NGC 4254 and the bridge of neutral hydrogen extending between the two entities.
Sensitive maps covering a much wider area, obtained at Westerbork Synthesis Radio Telescope (WSRT) and at Arecibo Observatory revealed that VIRGOHI21 is embedded within a much more extensive tail originating in NGC 4254.
[7] Other debris tails of this magnitude have been found to be common features in the Virgo cluster, where the high density of galaxies makes interactions frequent.
The original paper describing VIRGOHI21 as a dark galaxy provides several objections to the tidal-tail interpretation: that high-velocity interactions do not generally produce significant tails, that the high velocity needed is out-of-place in this part of the Virgo cluster and that the observed velocity profile is opposite from that expected in a tidal tail.
[10] Proponents of the tidal-tail interpretation counter these objections with simulations and argue that the apparently inverted velocity profile is due to the orientation of the tail with respect to Earth-based observers.