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The blue dot in this image marks the spot of
an energetic pulsar -- the magnetic, spinning core of star that blew up
in a supernova explosion. Image credit: NASA/JPL-Caltech/SAO.Full image and caption
Our Milky Way galaxy is littered with the still-sizzling remains of exploded stars.
When the most massive stars explode as supernovas, they don't fade
into the night, but sometimes glow ferociously with high-energy gamma
rays. What powers these energetic stellar remains?
NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, is helping
to untangle the mystery. The observatory's high-energy X-ray eyes were
able to peer into a particular site of powerful gamma rays and confirm
the source: A spinning, dead star called a pulsar. Pulsars are one of
several types of stellar remnants that are left over when stars blow up
in supernova explosions.
This is not the first time pulsars have been discovered to be the
culprits behind intense gamma rays, but NuSTAR has helped in a case that
was tougher to crack due to the distance of the object in question.
NuSTAR joins NASA's Chandra X-ray Observatory and Fermi Gamma-ray Space
Telescope, and the High Energy Stereoscopic System (H.E.S.S.) in
Namibia, each with its own unique strengths, to better understand the
evolution of these not-so-peaceful dead stars.
"The energy from this corpse of a star is enough to power the
gamma-ray luminosity we are seeing," said Eric Gotthelf of Columbia
University, New York. Gotthelf explained that while pulsars are often
behind these gamma rays in our galaxy, other sources can be as well,
including the outer shells of the supernova remnants, X-ray binary stars
and star-formation regions. Gotthelf is lead author of a new paper
describing the findings in the Astrophysical Journal.
In recent years, the Max-Planck Institute for Astronomy's H.E.S.S.
experiment has identified more than 80 incredibly powerful sites of
gamma rays, called high-energy gamma-ray sources, in our Milky Way. Most
of these have been associated with prior supernova explosions, but for
many, the primary source of observed gamma rays remains unknown.
The gamma-ray source pinpointed in this new study, called HESS
J1640-465, is one of the most luminous discovered so far. It was already
known to be linked with a supernova remnant, but the source of its
power was unclear. While data from Chandra and the European Space
Agency's XMM-Newton telescopes hinted that the power source was a
pulsar, intervening clouds of gas blocked the view, making it difficult
NuSTAR complements Chandra and XMM-Newton in its capability to detect
higher-energy range of X-rays that can, in fact, penetrate through this
intervening gas. In addition, the NuSTAR telescope can measure rapid
X-ray pulsations with fine precision. In this particular case, NuSTAR
was able to capture high-energy X-rays coming at regular fast-paced
pulses from HESS J1640-465. These data led to the discovery of PSR
J1640-4631, a pulsar spinning five times per second -- and the ultimate
power source of both the high-energy X-rays and gamma rays.
How does the pulsar produce the high-energy rays? The pulsar's strong
magnetic fields generate powerful electric fields that accelerate
charged particles near the surface to incredible speeds approaching that
of light. The fast-moving particles then interact with the magnetic
fields to produce the powerful beams of high-energy gamma rays and
"The discovery of a pulsar engine powering HESS J1640-465 allows
astronomers to test models for the underlying physics that result in the
extraordinary energies generated by these rare gamma-rays sources,"
"Perhaps other luminous gamma-ray sources harbor pulsars that we
can't detect," said Victoria Kaspi of McGill University, Montreal,
Canada, a co-author on the study. "With NuSTAR, we may be able to find
more hidden pulsars."
The new data also allowed astronomers to measure the rate at which
the pulsar slows, or spins down (about 30 microseconds per year), as
well as how this spin-down rate varies over time. The answers will help
researchers understand how these spinning magnets -- the cores of dead
stars -- can be the source of such extreme radiation in our galaxy.
NuSTAR is a Small Explorer mission led by Caltech and managed by
NASA's Jet Propulsion Laboratory in Pasadena, California, for NASA's
Science Mission Directorate in Washington. The spacecraft was built by
Orbital Sciences Corporation in Dulles, Virginia. Its instrument was
built by a consortium including Caltech, JPL, the University of
California, Berkeley, Columbia University, New York, NASA's Goddard
Space Flight Center, Greenbelt, Maryland, the Danish Technical
University in Denmark, Lawrence Livermore National Laboratory in
Livermore, California, ATK Aerospace Systems in Goleta, California, and
with support from the Italian Space Agency (ASI) Science Data Center.
NuSTAR's mission operations center is at UC Berkeley, with the ASI
providing its equatorial ground station located in Malindi, Kenya. The
mission's outreach program is based at Sonoma State University, Rohnert
Park, California. NASA's Explorer Program is managed by Goddard. JPL is
managed by Caltech for NASA.