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Messier 15 or M15 (also designated NGC 7078) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764. At an estimated 12.0 billion years old, it is one of the oldest known globular clusters. ==Characteristics== M15 is about 33,600 light-years from Earth, and 175 light years in diameter.〔 It has an absolute magnitude of -9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.〔 〕 Home to over 100,000 stars,〔http://www.astropix.com/HTML/SHOW_DIG/M15_Pease1.HTM〕 the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15 C. M15 also contains Pease 1, the first planetary nebula discovered within a globular cluster〔 〕 in 1928. Just three others have been found in globular clusters since then.〔http://messier.seds.org/more/m015_h2.html〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Messier 15」の詳細全文を読む スポンサード リンク
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