A blast from its past dates the youngest neutron-star binary

The youngest member of an important class of objects in space has been found by a team that includes Penn State Distinguished Professor of Astronomy and Astrophysics Niel Brandt. 

This composite image shows the energies streaming toward Earth from this object -- X-rays in blue and the radio emission in purple.

These energy detections have been overlaid in this image on an optical field of view from the Digitized Sky Survey. 

This discovery allows scientists to study a critical phase after a supernova and the birth of a neutron star. 

Credit: X-ray: NASA/CXC /Univ. of Wisconsin-Madison /S. Heinz et al; Optical: DSS; Radio: CSIRO/ATNF/ATCA

X-rays streaming toward Earth from the region near a neutron star that is cannibalizing its companion star have revealed the pair to be the youngest "X-ray binary" yet known.

The discovery by a team that includes a Penn State astronomer is being published in this week's issue of the The Astrophysical Journal.

The team discovered the age of this record-breaking pair, named Circinus X-1, by using data from NASA's Chandra X-ray Observatory, which revealed faint remnants of the supernova explosion that created the neutron star.

"I have been perplexed by the unusually strong evolution of the orbit of Circinus X-1 since my graduate-school days," said Niel Brandt, Distinguished Professor of Astronomy and Astrophysics.

"The discovery now of this system's youth provides a satisfying explanation for why its orbit evolves so strongly—because the system likely still is settling down after its violent birth."

The research team, which was led by Sebastian Heinz at the University of Wisconsin-Madison, determined that Circinus X-1 is less than 4,600 years old.

"X-ray binaries provide us with opportunities to study matter under extreme conditions that would be impossible to recreate in a laboratory," Heinz said.

"For the first time, we can study a newly minted neutron star in an X-ray binary system."

This is an artist's conception of the life of X-ray binary systems and the young and turbulent history of Circinus X-1, which formed in a supernova explosion less than 4,600 years ago, approximately 500 B.C.E., making it the youngest known X-ray binary. 

Credit: University of Wisconsin-Madison

X-ray binaries are star systems made up of two parts: a compact stellar remnant—either a neutron star or a black hole; and a companion star—a normal star like our Sun.

The new discovery, made in parallel with a radio telescope in Australia, provides scientists with unique insight into the formation of neutron stars and supernovas, and the effect of the supernova's explosion on a nearby companion star.

As the two objects orbit one another, the neutron star or black hole pulls in gas from the companion star, heating the gas to millions of degrees, producing intense X-ray radiation, and making these star systems some of the brightest X-ray sources in the sky.

To determine the age of Circinus X-1, the astronomers needed to examine the material around the orbiting pair of stars.

However, the overwhelming brightness of the neutron star made it too difficult for researchers to observe that interstellar gas.

The team recently caught a break, however, when they observed the neutron star in a very faint state—dim enough for scientists to detect the X-rays from the supernova shock wave that plowed through the surrounding interstellar gas.

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Youngest-Known Supernova Remnants in the Milky Way Galaxy

G306.3–0.9 in context with star-formation regions in southern Centaurus. Chandra X-ray observations (blue), Spitzer infrared data (red, cyan), and radio observations (purple) from the Australia Telescope Compact Array are merged in this composite.

The image is one degree across, which corresponds to 450 light-years at the remnant's estimated distance. 

Credit: X-ray: NASA/CXC/Univ. of Michigan/M. Reynolds et al; Infrared: NASA/JPL-Caltech; Radio: CSIRO/ATNF/ATCA

While performing an extensive X-ray survey of our galaxy's central regions, NASA's Swift satellite has uncovered the previously unknown remains of a shattered star. The full report here and at NASA Goddard

Designated G306.3-0.9 after the coordinates of its sky position, the new object ranks among the youngest-known supernova remnants in our Milky Way galaxy.

"Astronomers have previously cataloged more than 300 supernova remnants in the galaxy," said lead scientist Mark Reynolds, a postdoctoral researcher at the University of Michigan in Ann Arbor.

"Our analysis indicates that G306.3-0.9 is likely less than 2,500 years old, making it one of the 20 youngest remnants identified."

Astronomers estimate that a supernova explosion occurs once or twice a century in the Milky Way.

The expanding blast wave and hot stellar debris slowly dissipate over hundreds of thousands of years, eventually mixing with and becoming indistinguishable from interstellar gas.

Like fresh evidence at a crime scene, young supernova remnants give astronomers the best opportunity for understanding the nature of the original star and the details of its demise.

Supernova remnants emit energy across the electromagnetic spectrum, from radio to gamma rays, and important clues can be found in each energy band.

X-ray observations figure prominently in revealing the motion of the expanding debris, its chemical content, and its interaction with the interstellar environment, but supernova remnants fade out in X-ray light after 10,000 years.

Indeed, only half of those known in the Milky Way galaxy have been detected in X-rays at all.

Reynolds leads the Swift Galactic Plane Survey, a project to image a two-degree-wide strip along the Milky Way's central plane at X-ray and ultraviolet energies at the same time. Imaging began in 2011 and is expected to complete this summer.

"The Swift survey leverages infrared imaging previously compiled by NASA's Spitzer Space Telescope and extends it into higher energies," said team member Michael Siegel, a research associate at the Swift Mission Operations Center (MOC) in State College, Pa., which is operated by Penn State University.

"The infrared and X-ray surveys complement each other because light at these energies penetrates dust clouds in the galactic plane, while the ultraviolet is largely extinguished."

On Feb. 22, 2011, Swift imaged a survey field near the southern border of the constellation Centaurus.

Although nothing unusual appeared in the ultraviolet exposure, the X-ray image revealed an extended, semi-circular source reminiscent of a supernova remnant.

A search of archival data revealed counterparts in Spitzer infrared imagery and in radio data from the Molonglo Observatory Synthesis Telescope in Australia.

To further investigate the object, the team followed up with an 83-minute exposure using NASA's Chandra X-ray Observatory and additional radio observations from the Australia Telescope Compact Array (ATCA), located near the town of Narrabri in New South Wales.

"The fantastic sensitivity of ATCA has enabled us to image what, at radio wavelengths, turns out to be the dimmest remnant we have ever seen in our galaxy," said team member Cleo Loi, an undergraduate student at the University of Sydney who led the analysis of the radio observations.

A paper describing the team's findings will appear in an upcoming edition of The Astrophysical Journal and was published online on Friday.

Using an estimated distance of 26,000 light-years for G306.3-0.9, the scientists determined that the explosion's shock wave is racing through space at about 1.5 million mph (2.4 million km/h).

The Chandra observations reveal the presence of iron, neon, silicon and sulfur at temperatures exceeding 50 million degrees F (28 million C), a reminder not only of the energies involved but of the role supernovae play in seeding the galaxy with heavy elements produced in the hearts of massive stars.

"We don't yet have enough information to determine what type of supernova this was and therefore what type of star exploded, but we've planned a further Chandra observation to improve the picture," said coauthor Jamie Kennea, also a researcher at the Swift MOC.

"We see no compelling evidence that the explosion formed a neutron star, and this is something we hope can be determined one way or the other by future work."

Supernova Explosion: Galaxy's Youngest Black Hole

W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The highly distorted supernova remnant shown in this image may contain the most recent black hole formed in the Milky Way galaxy. 

The image combines X-rays from NASA's Chandra X-ray Observatory in blue and green, radio data from the NSF's Very Large Array in pink, and infrared data from Caltech's Palomar Observatory in yellow.

The remnant, called W49B, is about a thousand years old, as seen from Earth, and is at a distance of about 26,000 light years away.

The supernova explosions that destroy massive stars are generally symmetrical, with the stellar material blasting away more or less evenly in all directions.

However, in the W49B supernova, material near the poles of the doomed rotating star was ejected at a much higher speed than material emanating from its equator. Jets shooting away from the star's poles mainly shaped the supernova explosion and its aftermath.

By tracing the distribution and amounts of different elements in the stellar debris field, researchers were able to compare the Chandra data to theoretical models of how a star explodes.

For example, they found iron in only half of the remnant while other elements such as sulfur and silicon were spread throughout. This matches predictions for an asymmetric explosion.

Also, W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The authors also examined what sort of compact object the supernova explosion left behind. Most of the time, massive stars that collapse into supernovas leave a dense spinning core called a neutron star.