四级练习2015.01.27
[audio]http://sound.yywz123.com/tingbbs/cet4/cet420150127.mp3[/audio]An orbiting NASA telescope has detected evidence of what may be the youngest black hole yet discovered, relatively (1)__________________________. The object resulted from a supernova first observed by an American amateur astronomer just 3 decades ago.The astronomer, a school teacher named Gus Johnson, first observed the massive explosion that was labeled Supernova 1979C. Observations in the years since found it was a powerful source of X-rays typical of black holes.
(2)__________________________; their gravitational pull is so strong, that not even light can escape. They can form at the end of a star's life. When a star has used up its nuclear fuel, its core can collapse and it becomes a supernova. Daniel Patnaude, of the Harvard-Smithsonian Center for Astrophysics, who led a new study of this presumed black hole, says sometimes the result is a black hole, other times it's a neutron star.
"Results such as this might actually be important because we don't know (3)__________________________those supernova which form black holes, and those which form neutron stars."
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