Leo Ring

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Coordinates: Sky map 10h 48m 19.0s, +12° 41′ 21″

Leo Ring
Interstellar cloud
Intergalactic cloud
H I region
Observation data: J2000.0 [1][2] epoch
Right ascension 10h 48m 19.0s [2]
Declination +12° 41′ 21″ [2]
Distance 38±4.6×106 [2] ly   (11.8±1.4×106 [2] pc)
Constellation Leo
Physical characteristics
Radius 325×103 [3] ly   (100×103 [4] pc)
See also: Lists of nebulae

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.

Observation history[edit]

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 found that the gas was not primordial, but the result of a galactic collision between the two galaxies the ring is closely associated with.[3]

Formation history[edit]

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.[3][4]

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.[3][4]


  1. ^ "NAME LEO RING -- HI (21cm) source". SIMBAD. 
  2. ^ a b c d e "Leo Ring". NASA/IPAC Intergalactic Database. 
  3. ^ a b c d 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. 
  4. ^ a b c 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. 
  5. ^ "New stars from old gas surprise astronomers". PhysOrg.com. 18 February 2009. Retrieved 18 February 2009.