|H I region|
|Observation data: J2000.0  epoch|
|Right ascension||10h 48m 19.0s |
|Declination||+12° 41′ 21″ |
|Distance||38±4.6×106  ly (11.8±1.4×106  pc)|
|Radius||325×103  ly (100×103  pc)|
The Leo Ring is an immense intergalactic cloud of hydrogen and helium gas some 650 kilolight-years (200 kpc) in diameter, in orbit of two galaxies, in the center of the Leo Group of galaxies, within the constellation of Leo.
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.  In 2010, it was found that the gas was not primordial, but the result of a galactic collision between the two galaxies the ring is closely associated with.
A 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.
The two galaxies have now drifted to being 38 Mly (12 Mpc) apart, and 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.
- "NAME LEO RING -- HI (21cm) source". SIMBAD.
- "Leo Ring". NASA/IPAC Intergalactic Database.
- Léo Michel-Dansa, Pierre-Alain Duc (2010). "The mysterious Leo giant gas ring explained by a billion year old collision between two galaxies". Canada France Hawaii Telescope.
- Michel-Dansac, Leo; Duc, Pierre-Alain; Bournaud, Frederic; Cuillandre, Jean-Charles; Emsellem, Eric; Oosterloo, Tom; Morganti, Raffaella; Serra, Paolo; Ibata, Rodrigo; (2010). "A collisional origin for the Leo ring". The Astrophysical Journal Letters (July 2010) 717 (2): L143–L148. arXiv:1005.4208. Bibcode:2010ApJ...717L.143M. doi:10.1088/2041-8205/717/2/L143.
- "New stars from old gas surprise astronomers". PhysOrg.com. 18 February 2009. Retrieved 18 February 2009.
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