Leo Ring

Radio astronomers discovered the cloud in 1983. Astronomers had theorized that the ring was primordial gas in the process of forming a galaxy. The GALEX satellite detected ultraviolet emissions that astronomers at Johns Hopkins University and the Carnegie Institution for Science interpret to indicate star creation in newly forming dwarf galaxies in a 19 February 2009 Nature paper.^[5] In 2010, it was suggested that the gas was not primordial, but instead the result of a galactic collision between the two galaxies with which the ring is closely associated.^[3]

In 2021, analysis of several dense areas revealed several H II regions, powered by massive stars, a few which are O-type stars.^[6]

It has been suggested that 1.2 billion years ago, NGC 3384 collided with M96, at the heart of the Leo Group, expelling a galaxy's worth of gas into intergalactic space. This gas gathered into a vast set of clouds, the Leo Ring.^[3][4]

The ring is now 650 kilolight-years (200 kpc) wide. The ring is composed of a collection of H I regions. A bridge of gas connects the ring to M96.^[3][4]