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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Astronomers unravel 20-year dark matter mystery with new computer models

The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. 

The Milky Way is, like all large galaxies, thought to have formed from smaller galaxies in the early days of the Universe.

These small galaxies should also contain many very old stars, just as the Milky Way does, and a team of astronomers has now shown that this is indeed the case.

This image was composed from data from the Digitized Sky Survey 2. 

Credit: ESO /Digitized Sky Survey 2

Astronomers at the University of Texas at Austin believe they have discovered the answer to a 20-year debate over how the mysterious cosmic "dark matter" is distributed in small galaxies.

John Jardel 

Graduate student John Jardel and his advisor Karl Gebhardt found that the distribution, on average, follows a simple law of decreasing density from the galaxy's center, although the exact distribution often varies from galaxy to galaxy.

The findings are published today in The Astrophysical Journal Letters.

Dark matter is matter that gives off no light, but that astronomers detect by seeing its gravitational tug on other objects (like stars).

Theories abound on what dark matter might be made of—unseen particles, dead stars, and more—but nobody knows for sure.

Though mysterious, understanding the nature of dark matter is important, because it makes up most of the matter in the universe.

The only way to understand how the cosmos evolved to its present state is to decode dark matter's role.

For that reason, astronomers study the distribution of dark matter within galaxies and on even larger scales.

The Lonestar supercomputer is a resource of the Texas Advanced Computing Center (TACC) at The University of Texas at Austin. 

It is a Dell Linux cluster with 5,840 processing cores, and a peak performance of 62 teraflops (62 trillion floating-point operations per second). 

Since its launch in 2006, Lonestar has provided more than 85 million computing hours to approximately 1,100 researchers across the nation. Credit: TACC/UT-Austin

Dwarf galaxies, in particular, make great laboratories to study dark matter, Jardel says, because they contain up to 1,000 times more dark matter than normal matter.

Normal galaxies like the Milky Way, on the other hand, contain only 10 times more dark matter than normal matter.

For the past 20 years, observational astronomers and theorists have debated how dark matter is distributed in galaxies.

Observational astronomers, through their studies of telescope data, have argued that galaxies have a fairly uniform distribution of dark matter throughout.

Theorists, backed by computer simulations from the 1990s, have argued that dark matter density decreases steadily from a galaxy's core to its hinterlands. The disagreement is known as the "core/cusp debate."

Jardel's work set out to study the question using both data from telescopes and newly developed computer modeling. The project started out "not assuming core or cusp theory is right," he says, "but just asking 'what is it?.' These new models allowed us to take this approach."

Jardel used telescope observations of several of the satellite galaxies orbiting the Milky Way, including the Carina, Draco, Fornax, Sculptor, and Sextans dwarf galaxies.

The work involved running many supercomputer models for each galaxy to determine the distribution of dark matter within it, using the university's Texas Advanced Computing Center (TACC).

More information: dx.doi.org/10.1088/2041-8205/775/1/L30

NASA Chandra Image: Was Kepler's supernova unusually powerful?

This composite image of Kepler's supernova remnant shows different colors ranging from lower to higher energies: red, yellow, green, blue and purple.

An optical image from the Digitized Sky Survey (pale yellow and blue) shows stars in the field. 

The Kepler supernova was a Type Ia event, the thermonuclear explosion of a white dwarf. 

New analysis suggests that the supernova explosion was not only more powerful, but might have also occurred at a greater distance, than previously thought. 

Credit: X-ray: NASA/CXC/SAO/D.Patnaude, Optical: DSS

Astronomers have long studied the Kepler supernova remnant and tried to determine exactly what happened when the star exploded to create it.

New analysis of a long observation from NASA's Chandra X-ray Observatory is providing more clues.

This analysis suggests that the supernova explosion was not only more powerful, but might have also occurred at a greater distance, than previously thought.

This image shows the Chandra data derived from more than 8 days worth of observing time. The X-rays are shown in five colours from lower to higher energies: red, yellow, green, blue, and purple.

These various X-ray slices were then combined with an optical image from the Digitized Sky Survey, showing stars in the field.

Previous analysis of this Chandra image has determined that the stellar explosion that created Kepler was what astronomers call a "Type Ia" supernova.

Illustration: NASA/CXC/M.Weiss

This class of supernovas occurs when a white dwarf gains mass, either by pulling gas off a companion star or merging with another white dwarf, until it becomes unstable and is destroyed by a thermonuclear explosion.

Unlike other well-known Type Ia supernovas and their remnants, Kepler's debris field is being strongly shaped by what it is running into.

More specifically, most Type Ia supernova remnants are very symmetrical, but the Kepler remnant is asymmetrical with a bright arc of X-ray emission in its northern region.

This indicates the expanding ball of debris from the supernova explosion is plowing into the gas and dust around the now-dead star.

Read more in the AstroPhysical Journal