M100 is a member of the huge virgo cluster of an estimated 2 , 500 galaxies M100是室女座中2500个河外星系（据估计）中的一个，该星系天文业余爱好者可观测。
2.
Tens of supernovae are discovered each year . however , they are not in our galaxy and usually very dim . here is one in m51 in 1994 天文学家每年会发现十数至数十颗超新星，但大部分都位于偏远而暗淡的河外星系，这是1994年在m51发现的超新星。
3.
" every galaxy contains a black hole , and there are millions or billions of galaxies . in principle , we are expecting these events to happen all the time , " said prof hasinger 照他的意思应该银河系的核心也是一个黑洞.离银河系最近的两个河外星系麦哲伦星云和仙女座大星云好像都有黑洞
