Dark Energy Illustration
A study using Chandra, XMM-Newton and Sloan Digital Sky Survey (SDSS) data suggests that dark energy may have varied over cosmic time. This artist's illustration helps explain how astronomers tracked the effects of dark energy to about one billion years after the Big Bang by determining the distances to nearly 1,600 quasars, rapidly growing black holes that shine extremely brightly.
(Illustration Credit: NASA/CXC/M.Weiss)

X-ray Images of PSS 0133+0400 and PSS 0955+5940
Scientists used Chandra and other telescopes to study this event and determine the spin rate of the black hole, a fundamental property that has been difficult for astronomers to measure.
(Credit: NASA/CXC/Univ. of Florence/G.Risaliti & E.Lusso )