Free Astronomy Magazine July-August 2014

5 STELLAR EVOLUTION JULY-AUGUST 2014 at the origin s L ying nearly 16,000 light-years away from Earth, in the southern constella- tion Ara, there is the most massive and compact open star cluster of our gal- axy and entire Local Group. This cluster contains the equivalent of 100,000 solar masses in stars of any size and interstellar gases, all concentrated in a region about 6 light-years across. Among the hundreds of stars crowded into that tiny corner of the sky, there are several blue, yellow, red giants and supergiants, as well as an un- usually high number of Wolf-Rayet stars (giants that shed their mass due to strong stellar winds and which are characterized by very high surface temperatures). A clus- ter of that magnitude, located at a some- what modest distance from us, should ap-