APOD: March 12, 1999 - Hydrogen, Helium, and the Stars of M10 (original) (raw)

Astronomy Picture of the Day

Discover the cosmos!Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

March 12, 1999

Hydrogen, Helium, and the Stars of M10
Credit and Copyright: Till Credner, Sven Kohle(Bonn University),Hoher List Observatory

Explanation: Stars like the Sun use hydrogen for fuel, "burning" hydrogen into helium at their coresthrough nuclear fusion. But what happens when that hydrogen runs out? For a while, hydrogen burns in a shell surrounding the stellar core and the star expands to become a red giant. The bright reddish-orange stars inthis beautiful two-color compositepicture of the oldglobular star cluster M10 are examples of this phaseof stellar evolution. Yet the bright blue stars apparent in M10 have evolved beyond the simple, hydrogen shell burning stage. These stars have become "horizontal branch" giants with core temperatures hot enoughto burn helium into carbon. In this image, only the barely visible, faint, gray-looking stars are likelyto still be burning hydrogen at their cores.

Tomorrow's picture: Phobos Over Mars

Authors & editors: Robert Nemiroff(MTU) &Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris.Specific rights apply.
A service of: LHEAatNASA/GSFC
& Michigan Tech. U.