Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 August 5
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X-ray Echoes from Circinus X-1
Image Credit: X-ray - NASA/CXC/Univ. Wisconsin-Madison/S.Heinz et al, Optical - DSS

Explanation: Circinus X-1 is an X-ray binary star known for its erratic variability. In the bizarre Circinus X-1 system, a dense neutron star, the collapsed remnant of a supernova explosion, orbits with a more ordinary stellar companion. Observations of the X-ray binary in months following an intense X-ray flare from the source in 2013 progressively revealed striking concentric rings - bright X-ray light echoes from four intervening clouds of interstellar dust. In this X-ray/optical composite, the swaths of Chandra Observatory X-ray image data showing partial outlines of the rings are in false colors. Remarkably, timing the X-ray echoes, along with known distances to the interstellar dust clouds, determines the formerly highly uncertain distance to Circinus X-1 itself to be 30,700 light-years.

Tomorrow's picture: pixels in space

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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