Credit: X-ray: NASA/CXC/Uni. of Science and Technology of China/Y. Xue et al;
Optical: NASA/STScI
These images show the location of an event, discovered by NASA's Chandra X-ray Observatory, that likely signals the merger of two neutron stars. A bright burst of X-rays
in this source, dubbed XT2, could give astronomers fresh insight into
how neutron stars — dense stellar objects packed mainly with neutrons —
are built.
XT2 is located in a galaxy about 6.6 billion light years
from Earth. The source is located in the Chandra Deep Field South
(CDF-S), a small patch of sky in the Fornax constellation. The CDF-S is
the deepest X-ray image ever taken,
containing almost 12 weeks of Chandra observing time. The wider field
of view shows an optical image from the Hubble Space Telescope of a
portion of the CDF-S field, while the inset shows a Chandra image
focusing only on XT2. The location of XT2, which was not detected in
optical images, is shown by the rectangle, and its host galaxy is the
small, oval-shaped object located slightly to the upper left.
On March 22, 2015, astronomers saw XT2 suddenly appear in the Chandra
data and then fade away after about seven hours. By combing through the
Chandra archive, they were able to piece together the history of the
source's behavior. The researchers compared the data from XT2 to
theoretical predictions made in 2013 of what the X-ray signature from
two colliding neutron stars without a corresponding gamma ray bursts
would look like.
When two neutron stars merge they produce jets of high energy
particles and radiation fired in opposite directions. If the jet is
pointed along the line of sight to the Earth, a flash, or burst, of gamma rays
can be detected. If the jet is not pointed in our direction, a
different signal is needed to identify the merger. This result provides
scientists with an opportunity to study just such a case.
X-rays from XT2 showed a characteristic signature that matched those predicted for a newly-formed magnetar,
that is, a neutron star spinning around hundreds of times per second
and possessing a tremendously strong magnetic field about a quadrillion
times that of Earth's.
The team think that the magnetar lost energy in the form of an
X-ray-emitting wind, slowing down its rate of spin as the source faded.
The amount of X-ray emission stayed roughly constant in X-ray brightness
for about 30 minutes, then decreased in brightness by more than a
factor of 300 over 6.5 hours before becoming undetectable. This showed
that the neutron star merger produced a new, larger neutron star and not
a black hole.
XT2's bright flare of X-rays gives astronomers another signal — in
addition to the detection of gravitational waves — to probe neutron star
mergers.
A paper describing these results
appeared in the April 11th issue of Nature, led by Yongquan Xue
(University of Science and Technology in China). NASA's Marshall Space
Flight Center in Huntsville, Alabama, manages the Chandra program for
NASA's Science Mission Directorate in Washington. The Smithsonian
Astrophysical Observatory in Cambridge, Massachusetts, controls
Chandra's science and flight operations.
Timelapse
Credit: NASA/CXC/Uni. of Science and Technology of China/Y. Xue et al.
Credit: NASA/CXC/Uni. of Science and Technology of China/Y. Xue et al.
When two neutron stars merge they produce jets of high energy
particles and radiation fired in opposite directions. If the jet is
pointed along the line of sight to the Earth, a flash, or burst, of gamma rays
can be detected. If the jet is not pointed in our direction, a
different signal is needed to identify the merger. This result provides
scientists with an opportunity to study just such a case.
X-rays from XT2 showed a characteristic signature that matched those predicted for a newly-formed magnetar,
that is, a neutron star spinning around hundreds of times per second
and possessing a tremendously strong magnetic field about a quadrillion
times that of Earth's.
The team think that the magnetar lost energy in the form of an
X-ray-emitting wind, slowing down its rate of spin as the source faded.
The amount of X-ray emission stayed roughly constant in X-ray brightness
for about 30 minutes, then decreased in brightness by more than a
factor of 300 over 6.5 hours before becoming undetectable. This showed
that the neutron star merger produced a new, larger neutron star and not
a black hole.
XT2's bright flare of X-rays gives astronomers another signal — in
addition to the detection of gravitational waves — to probe neutron star
mergers.
A paper describing these results
appeared in the April 11th issue of Nature, led by Yongquan Xue
(University of Science and Technology in China). NASA's Marshall Space
Flight Center in Huntsville, Alabama, manages the Chandra program for
NASA's Science Mission Directorate in Washington. The Smithsonian
Astrophysical Observatory in Cambridge, Massachusetts, controls
Chandra's science and flight operations.
Fast Facts for CDF-S XT2:
Scale: Chandra images are about 15 arcsec (360,000 light years) across.
Category: Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 3h 32m 18.38s | Dec -27° 52´ 24.2"
Constellation: Fornax
Observation Date: Mar 22, 2015
Observation Time: 19 hours 27 minutes
Obs. ID: 16453
Instrument: ACIS
References: Xue,Y.Q et al, 2019, Nature. arXiv:1904.05368
Color Code: X-ray: Orange; Optical: Red
Distance Estimate: About 6.6 billion light years
Source: NASA’s Chandra X-ray Observatory
