In late 2013, when the neutron¹ star at the heart of one of our galaxy²'s oddest supernovae gave off a massive burst of X-rays, the resulting echoes -- created when the X-rays bounced off clouds of dust in interstellar space -- yielded a surprising new measuring stick for astronomers³. Circinus X-1 is a freak of the Milky⁴ Way. Located in the plane of the galaxy, Circinus X-1 is the glowing husk of a binary⁵ star system that exploded a mere⁶ 2,500 years ago. The system consists of a nebula⁷ and a neutron star, the incredibly dense⁸ collapsed⁹ core of the exploded star, still in the orbital embrace of its companion star.

 

The system is called an X-ray binary because it emits X-rays as material from the companion star spirals onto the much denser¹⁰ neutron star and is heated to very high temperatures.

 

"In late 2013, the neutron star underwent an enormous outburst for about two months, during which it became one of the brightest sources in the X-ray sky," explains University of Wisconsin-Madison astronomy Professor Sebastian Heinz. "Then it turned dark again."

 

The flicker¹¹ of X-rays from the odd binary system was monitored by a detector¹² aboard the International Space Station. Heinz and his colleagues quickly mounted a series of follow-up observations with the space-based Chandra and XMM-Newton telescopes to discover four bright rings of X-rays, like ripples¹³ in a cosmic pond, all around the neutron star at the heart of Circinus X-1. 

 

Their observations were reported June 23 in The Astrophysical Journal.

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