RCW 36 (also designated Gum 20)[5] is an emission nebula containing an open cluster in the constellation Vela.

Stars form when the mass gas in part of a cloud becomes too great, causing it to collapse due to the Jeans instability.

[11] Early maps of the region were produced by radio telescopes that traced emission from several types of molecules found in the clouds, including CO, OH, and H2CO.

In the dense gas at the western edge of RCW 36, where the far-infrared emission is greatest, are found protostellar cores, the Herbig Haro objects, and an ultra-compact H II region.

[4] The H II region is an area around the cluster in which hydrogen atoms in the interstellar medium have been ionized by ultraviolet light from O- and B-type stars.

These stars are still in the process of contraction before they reach the main sequence, and they may still have gas accreting onto them from either a circumstellar disk or envelope.

Bright infrared sources, attributed to massive stars, were first identified by the TIFR 100-cm balloon-born telescope from the National Balloon Facility in Hyderabad, India.

[3] Observations by NASA's Spitzer Space Telescope and Chandra X-ray Observatory were used to identify cluster members as part of the MYStIX survey of nearby star-forming regions.

[6] In the MYStIX catalog of 384 probable young stellar members of RCW 36, more than 300 of the stars are detected by X-ray sources.

[4] The young star CXOANC J085932.2−434602 was observed by the Chandra X-ray Observatory to have produced a large flare with a peak temperature greater than 100 million kelvins.