NGC 4666 is a spiral galaxy in the equatorial constellation of Virgo, located at a distance of approximately from the Milky Way. It was discovered by the German-born astronomer William Herschel on February 22, 1784. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. John L. E. Dreyer described it as "bright, very large, much extended 45ðñ, pretty suddenly brighter middle". It is a member of an interacting system with NGC 4668 and a dwarf galaxy, and belongs to a small group that also includes NGC 4632, that is known as the NGC 4666 Group.
The morphological classification of this galaxy is SABc, which indicates a weak bar around the nucleus with moderately wound spiral arms. Viewed nearly edge-on, its galactic plane is inclined at an angle of to the line of sight from the Earth, with the major axis aligned along a position angle of 40ð. There is an active galactic nucleus that shows a modest level of activity and is most likely heavily obscured by gas and dust. The central point source has been detected in the radio and X-ray bands.
This is a starburst galaxy that is noteworthy for its vigorous star formation, which creates an unusual superwind of out-flowing gas. This wind is not visible at optical wavelengths, but is prominent in X-rays, and has been observed by the ESA XMM-Newton space telescope. The estimated star formation rate is yr<sup>âÂÂ1</sup>, with a density of yr<sup>âÂÂ1</sup> kpc<sup>âÂÂ2</sup>. Unlike in many other starburst galaxies, the star formation is spread across the disk rather than being more concentrated.
Three supernovae have been observed in NGC 4666: