Ring of Fire

Glowing blobs of gas look like flames shooting from the Necklace Nebula, the expanding remains of a star that was once like the Sun. The nebula actually contains two stars. Thousands of years ago, one of the stars expelled its outer layers into space, leaving behind its dense, hot core, known as a white dwarf. Ultraviolet energy from the white dwarf causes the surrounding gas and dust to glow. The bright "flames" are denser knots of material expelled in a ring about the dying star's equator. The nebula is about 15,000 light-years away, in the constellation Sagittarius. Hubble Space Telescope snapped the image, in which blue represents the glow of hydrogen, green is oxygen, and red is nitrogen. [NASA/ESA/Hubble Heritage Team]