A bizarre and sometimes frenetic source of X-rays in our Milky Way galaxy — a double star system — has provided astronomers with a new "measuring stick" to determine the distance to the unique object.
A massive burst of X-rays in late 2013 created echoes as the outpouring of energy bounced off clouds of interstellar dust, resulting in rings of X-ray light around the object dubbed Circinus X-1, rings detected by NASA's Chandra X-Ray Observatory.
Within Circinus X-1 is a neutron star, a dense surviving relic of a large, massive star that exploded as a supernova, orbiting another huge star in a thick shroud of interstellar dust and gas.
Surprisingly powerful high-energy particle streams coming from the cosmic pair have allowed scientists to make new, accurate measurements of its distance.
"It's really hard to get accurate distance measurements in astronomy and we only have a handful of methods," says Sebastian Heinz at the University of Wisconsin, Madison, who headed a study being published by The Astrophysical Journal.
However, he explains, in the same way bats utilize sonar to triangulate their position, X-rays from the Circinus X-1 object were used to determine exactly where the double-star system is.
Previous studies had come up with different figures for the distance between Earth and Circinus X-1, but the new study has yielded a definitive answer, the researchers say — 30,700 light years.
Reflecting off dust clouds between the star system and Earth cause X-rays released by the double-star system to arrive at the Earth from differing angles, and with different time delays, resulting in the rings observed by Chandra, the researchers explain.
Analysis of those echo rings combined with data from an Australian radio telescope, the Mopra instrument, allowed the scientists to apply simple geometry and precisely determine the orbiting cosmic pair's distance from the Earth.
"We like to call this system the "Lord of the Rings," but this one has nothing to do with Sauron," says study co-author Michael Burton of the University of New South Wales in Australia. "The beautiful match between the Chandra X-ray rings and the Mopra radio images of the different clouds is really a first in astronomy."
The researchers were surprised to see behaviors in the double-star system usually seen more frequently in systems with black holes than found in systems like Circinus X-1 with an orbiting neutron star.
Specifically, the double-star system has apparently surpassed a key level of brightness in which outward pressure from radiation emitted by the system is normally balanced by the inward pull from gravity, a behavior more suggestive of a massive black hole.
"Circinus X-1 acts in some ways like a neutron star and in some like a black hole," says co-author Catherine Braiding of the Australian university. "It's extremely unusual to find an object that has such a blend of these properties."
Astronomers estimate Circinus X-1 started emitting X-rays around 2,500 years ago, making it the youngest X-ray binary yet discovered.
