Image of Circinus X-1, an X-ray binary star system, taken
by the Chandra X-ray Observatory. (Credit: NASA)
Data from Supernova Blast Provides Clues to Determining Age of Binary Star Systemhas revealed faint remnants of a
supernova explosion and helped researchers determine Circinus X-1 -- an X-ray
binary -- is the youngest of this class of astronomical objects found to
date.
As the name suggests, 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. As they orbit one another, the
neutron star or black hole pulls in gas from the companion star. This heats 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.
Sebastian Heinz and his team at the University of Wisconsin-Madison (UW)
discovered Circinus X-1 is less than 4,600 years old, making it the youngest
X-ray binary system ever seen. This discovery, made in parallel with a radio
telescope in Australia, provides scientists unique insight into the formation of
neutron stars and supernovas, and the effect of the supernova's explosion on a
nearby companion star.
"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."
Astronomers have detected hundreds of X-ray binaries throughout the Milky Way
and other nearby galaxies. However, these older X-ray binaries, with ages
typically measured in millions of years, only reveal information about what
happens much later in the evolution of these systems.
"It's critical that we see what these X-ray binaries are doing at all stages
of their lives," said co-author Paul Sell, also of UW. "Circinus X-1 is showing
us what happens in a cosmic blink of an eye after one of these objects is
born."
To determine the age of Circinus X-1, the team of 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,
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.
"Since the supernova was triggered by the formation of the neutron star, our
limit on the age of the supernova remnant also limits the age of the neutron
star in Circinus X-1," said co-author Robert Fender of the University of Oxford
in the U.K.
The youth of Circinus X-1 helps explain its wild swings in brightness and the
highly unusual orbit of its two stars, which had puzzled astronomers for years.
The orbit is very eccentric -- non-circular -- and the period during which the
two stars orbit each other is decreasing by several minutes every year. This is
exactly what is expected for a young X-ray binary disrupted by a supernova
explosion before the gravitational pull of the stars on each other has had time
to circularize and stabilize the orbit.
Previous observations with other telescopes indicated the magnetic field of
the neutron star in Circinus X-1 is weak. That, in addition to the star system's
young age, has led to two possible theories: either a neutron star can be born
with a weak magnetic field, or it can quickly become de-magnetized as it pulls
material from its companion star onto itself. Neither conclusion was expected
from existing theories of neutron star evolution.
In our galaxy, the only other established X-ray binary within a supernova
remnant is SS 433, which is between 10,000 and 100,000 years old, and behaves in
many ways like an older version of Circinus X-1. Two other candidate X-ray
binaries in nearby galaxies have ages similar to SS 433.
In addition to the Chandra data, radio observations from the Australia
Telescope Compact Array were critical in these findings. A paper describing
these results is available online and appears in the Dec. 3 issue of The
Astrophysical Journal.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra
program for NASA's Science Mission Directorate in Washington. The Smithsonian
Astrophysical Observatory in Cambridge, Mass., controls Chandra's science and
flight operations.
For more information about Chandra, visit:
and
Guillermo Gonzalo Sánchez Achutegui
ayabaca@hotmail.clm
ayabaca@gmail.com
ayabaca@yahoo.com
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