An international team of astronomers has recently discovered a glowing supernova remnant, consisting of the remains of a star that exploded just 2,500 years ago. However, in digging a little deeper, the team stumbled across an astrophysical first for the Milky Way.
The Makeup of Circinus X-1
The observations were conducted by an international team that was led by University of Wisconsin-Madison astronomy professor Sebastian Heinz, harnessing the capabilities of NASA’s Chandra X-ray Observatory
and Australia Telescope Compact Array. The findings were published in the Astrophysical Journal on Dec. 3.
Heinz and colleagues commenced investigation into the constellation Circinus, some 24,000 to 30,000 light years from Earth. The group examined a neutron star, which is located in the X-ray binary system Circinus X-1. A binary system possesses two stars orbiting their common center of mass, comprising of a brighter, primary star and its companion star (a.k.a. the secondary). An X-ray binary system contains a nascent star that closely orbits a black hole or neutron star, with X-ray emissions triggered by material from the evolving star spiraling into its much denser companion; the material is then heated to extreme temperatures, resulting in the release of X-rays.
Circinus X-1 contains a neutron star, situated inside the glowing nebula, which still clings to its former companion. Neutron stars are the result of the gravitational collapse of massive stars, during a supernova event and often have masses of between 1.4 to three solar masses and densities that far surpass those of regular stars. The supernova event culminated in a supernova remnant (SNR), created by a shockwave that swept up ejected matter and interstellar material, as it expanded outward.
A Rare X-ray Binary System
Typically, most identified X-ray binary systems are relatively old and no longer possess supernova remnants. Discovering the shell of ionized gas, which serves as a indication of a supernova event, is rather uncommon. According to Heinz, the glowing remnant provides a “historical record” of the dramatic explosion. Since the supernova remnants only endure for a short period, they can act as astronomical clocks for finding recent phenomena.
Heinz goes on to discuss the youthful nature of the remnant; at just 2,500 years of age, he states that the system represents the youngest known X-ray binary. Meanwhile, former University of Wisconsin-Madison student Paul Sell, who was also involved in the study, analogizes of the team’s remarkable findings:
“In terms of a human lifetime, it would be roughly akin to a newborn just a few days old.”
It is incredibly rare to find neutron stars that remains in existence alongside their companion stars; approximately 100, or so, are known to exist within the Milky Way. Even more extraordinary is the discovery of the supernova remnant, which survives for up to around 100,000 years before dissipating amongst the surrounding gas and dust of space.
Heinz reflects upon the exciting, new discovery, explaining how it could serve as a novel laboratory for studying major theories of stellar evolution:
“Our observations solve a number of puzzles both about this object and the way that neutron stars evolve after they are born. For example, the unusual elliptical orbit on which these two stars swing around each other is exactly what you would expect for a very young X-ray binary.”
However, with new opportunities emerge new challenges to our existing understanding of space. It was commonly understood that neutron stars are born with large magnetic fields. Recent X-ray observations of the neutron star in Circinus X-1, on the other hand, do not appear to substantiate this theory. The authors consolidate these findings based upon the X-ray binary being so unique, in terms of its youth.
Ultimately, it is hoped that the Circinus X-1 X-Ray binary system will help to unlock further mysteries of space and will prove useful in testing our current knowledge and theories of space.
By James Fenner