Music 
Music 
Narrator: This is the supermassive black hole at the center of NGC 4151. 
The dark object in the middle is the black hole. Surrounding it is a 
flattened cloud of dust and gas, called an accretion disk. Recently, 
scientists using the XMM-Newton X-ray satellite showed that a mysterious 
source of X-ray flares actually lies high above the disk. About half an 
hour after each flare, the inner accretion disk lights up with an X-ray 
"echo." The delay is caused by the time it light from the flare to reach 
the disk. This is first clear measurement of the effect, and demonstrates 
that the flaring X-ray source lies well above the disk. With flares serving 
as "flash-bulbs," future X-ray telescope missions will be able to use their 
echoes to precisely map the environs of distant black holes. 
Beeping 
Beeping