NASA's Chandra Captures X-Ray Echoes Pinpointing Distant Neutron Star

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June 23, 2015

RELEASE 15-137

NASA's Chandra Captures X-Ray Echoes Pinpointing Distant Neutron Star

Astronomers using NASA's Chandra X-ray Observatory have discovered the
largest and brightest set of rings from X-ray light echoes ever observed.
These extraordinary rings, produced by an intense flare from a neutron star,
provide astronomers a rare chance to determine how far across the Milky Way
galaxy the star is from Earth.

The rings appear as circles around Circinus X-1, a double star system in the
plane of our galaxy containing a neutron star, the dense remnant of a massive
star pulverized in a supernova explosion. The neutron star is in orbit with
another massive star, and is shrouded by thick clouds of interstellar gas and
dust. Circinus X-1 is also the source of a surprisingly powerful jet of
high-energy particles.

"It's really hard to get accurate distance measurements in astronomy and
we only have a handful of methods," said Sebastian Heinz of the University
of Wisconsin in Madison, who led the study. "But just as bats use sonar to
triangulate their location, we can use the X-rays from Circinus X-1 to figure
out exactly where it is.'

The light echo shows that Circinus X-1 is located about 30,700 light years
from Earth, and settles the difference in results published in prior studies.
The detection and characterization of the rings required the unique
capabilities of Chandra -- the ability to detect fine details combined with
sensitivity to faint signals.

Researchers determined that the rings are echoes from a burst of X-rays
emitted by Circinus X-1 in late 2013. The burst reflected off intervening
clouds of dust, with some reflected X-rays arriving to Earth from different
angles at a time delay of about one to three months, creating the observed
rings.

By comparing the Chandra data to prior images of dust clouds detected by the
Mopra radio telescope in Australia, the researchers determined that each ring
was created by the X-ray reflections off a different dust cloud. The radio
data provides the distance to the different clouds and the X-ray echo
determines the location of Circinus X-1 relative to the clouds. An analysis
of the rings with the combined radio data allows researchers to use simple
geometry to accurately determine the distance of Circinus X-1 from Earth.

'We like to call this system the 'Lord of the Rings,' but this one has
nothing to do with Sauron," said co-author Michael Burton of the University
of New South Wales in Sydney, 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."

This new distance estimate means that Circinus X-1 is inherently much
brighter in X-rays and other types of light than some scientists previously
thought, and indicates that the star system has repeatedly passed a key
threshold for brightness where the outward pressure from radiation by the
system is balanced by the inward pull of gravity. This behavior is something
astronomers generally see more often in systems containing black holes than
in systems like Circinus X-1 that contain a neutron star.

The researchers also determined that the speed of the jet of high-energy
particles produced by the system is at least 99.9% of the speed of light.
This extreme velocity is usually associated with jets produced by a black
hole.

"Circinus X-1 acts in some ways like a neutron star and in some like a
black hole," said co-author Catherine Braiding, also of the University of
New South Wales. 'It's extremely unusual to find an object that has such
a blend of these properties."

Circinus X-1 is thought to have originally become an X-ray source about 2,500
years ago, as seen from Earth. This makes Circinus X-1 the youngest so-called
X-ray binary known. The new Chandra data allows astronomers to make a
detailed three-dimensional map of the dust clouds between Circinus X-1 and
us, providing a valuable probe of the structure of the galaxy.

These results have been published in The Astrophysical Journal and are
available online [1]. NASA's Marshall Space Flight Center in Huntsville,
Alabama, manages the Chandra program for the agency's Science Mission
Directorate in Washington. The Smithsonian Astrophysical Observatory in
Cambridge, Massachusetts, controls Chandra's science and flight operations.

For more Chandra images, multimedia and related materials, visit:

http://www.nasa.gov/chandra

For an interactive image, podcast, and video about these findings, visit:

http://chandra.si.edu

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