Fig7_13 Faint stars globular cluster

Fig7_13 Faint stars globular cluster

Fig. 7.13 . This five-day exposure from an instrument aboard the Hubble Space Telescope includes the faintest detectable stars in the globular star cluster NGC 6397, which is located about 8,500 light-years away from Earth. Some of these objects are white-dwarf stars, the collapsed, burned-out relics of former stars like the Sun. White dwarfs cool down at a predictable rate, which can be used to measure the age of this globular cluster, estimated to be about 12 billion years old. The crossed lines radiating from the bright stars are diffraction spikes caused by the struts that support the telescope mirror. (Courtesy of NASA/ESA/Harvey Richer, U. British Columbia.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University