Tài liệu tham khảo WikiPedia: NGC_4631 http://nedwww.ipac.caltech.edu/ http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=... http://apod.nasa.gov/apod/ap100517.html http://antwrp.gsfc.nasa.gov/apod/ap040123.html //hdl.handle.net/2060%2F19950011081 //arxiv.org/abs/astro-ph/0105541 //arxiv.org/abs/astro-ph/0607669 //doi.org/10.1086%2F171699 //doi.org/10.1086%2F175162 //doi.org/10.1086%2F323179
