Andrew Yee
December 20th 05, 10:00 PM
Istituto Nazionale di Astrofisica
(National Institute for Astrophysics)
Milan, Italy
Contact:
Patrizia Caraveo, INAF-Italian National Institute for Astrophysics
+39 02 23699326
December 13, 2005
Pulsar Racing Through Space Reveals Comet-Like Trail
Scientists have uncovered a new feature in one of the closest pulsars to
Earth, the Geminga pulsar. Plowing through space at 120 kilometers per
second (or Milan to New York City in 57 seconds), this dense nugget of a
dead star leaves in its wake a comet-like trail of high-energy electrons.
A team led by Dr. Patrizia Caraveo of the Italian National Institute for
Astrophysics (INAF) in Milan discovered this cometary trail with data from
NASA's Chandra X-ray Observatory Archive. The discovery follows the team's
discovery in 2003 using ESA's XMM-Newton of Geminga's twin X-ray tails
stretching for billions of chilometers.
Together, these observations provide unique insight into the contents and
density of the interstellar "ocean" Geminga is plowing through, as well as
the physics of Geminga itself. Not only is Geminga close, only about 500
light years from Earth, it is cutting across our line of sight, offering a
spectacular view of a pulsar in motion.
"Geminga is the only isolated pulsar we know of showing both a small
comet-like trail and a larger tail structure," said Dr. Andrea De Luca of
INAF's Istituto di Astrofisica Spaziale e Fisica Cosmica, lead author on
an article about this discovery in Astronomy & Astrophysics. "This
jettison from Geminga's journey through interstellar space provides
unprecedented information about the physics of pulsars."
A pulsar is a type of rapidly spinning neutron star that emits steady
pulses of radiation with each rotation, funnelled along strong magnetic
field lines, much like a lighthouse beam sweeping across space. A neutron
star is the core remains of an exploded star once at least eight times as
massive as the sun.
These dense stars, only about 20 kilometers across, still contain roughly
the mass of the sun. Neutron stars contain the densest material known.
Like many neutron stars, Geminga got a "kick" from the explosion that
created it and has been flying through space like a cannonball ever since.
De Luca said that Geminga's complex phenomenology of tails and a trail
must be from high-energy electrons escaping the pulsar magnetosphere
following paths clearly driven by the pulsar's motion in the interstellar
medium.
Most pulsars emit radio waves. Yet Geminga is "radio quiet" and was
discovered 30 years ago as a unique "gamma-ray only" source (only later
was Geminga seen in the X-ray and optical light wavebands). Geminga
generates gamma rays by accelerating electrons and positrons, a type of
antimatter, to high speeds as it spins like a dynamo four times per
second.
"Astronomers have known that only a fraction of these accelerated
particles produce gamma rays, and they have wondered what happens to the
remaining ones," said Caraveo, a co-author on the Astronomy & Astrophysics
article. "Thanks to the combined capabilities of Chandra and XMM-Newton,
we now know that such particles can escape. Once they reach the shock
front, created by the supersonic motion of the star, the particles lose
their energy radiating X-rays."
Meanwhile, an equal number of particles (with a different electric charge)
should move in the opposite direction, aiming back at the star. Indeed,
when they hit the star's crust they create tiny hotspots, which have been
detected through their varying X-ray emission.
The next generation of high-energy gamma-ray instruments -- namely, the
planned Italian Space Agency's AGILE mission and NASA's GLAST mission --
will explore the connection between the X-ray and gamma ray behaviour of
pulsars to provide clues to the nature of unknown gamma-ray sources,
according to Prof. Giovanni Bignami, a co-author and director of the
Centre d'Etude Spatiale des Rayonnements (CESR) in Toulouse, France. Of
the 271 higher-energy gamma-ray objects detected by a NASA telescope
called EGRET, 170 remained unidentified in other wavebands. These
unidentified objects could be "gamma-ray pulsars" like Geminga, whose
optical and X-ray light might be visible only because of its nearness to
Earth.
Only about a dozen other radio-quiet isolated neutron stars are known, and
Geminga is the only one with tails and trails and copious gamma-ray
emission. Bignami named Geminga for "Gemini gamma-ray source" in 1973. In
his local Milan dialect, the name is a pun on "ghè minga," which means "it
is not there." Indeed, Geminga was unidentified in other wavelengths until
1993, twenty years after its discovery.
The discovery team also includes Drs. Fabio Mattana and Alberto Pellizzoni
of the INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica.
[NOTE: An image supporting this release is available at
http://www.inaf.it/comunicati_stampa/cs161205/xmm_chandra.jpg (324KB) ]
(National Institute for Astrophysics)
Milan, Italy
Contact:
Patrizia Caraveo, INAF-Italian National Institute for Astrophysics
+39 02 23699326
December 13, 2005
Pulsar Racing Through Space Reveals Comet-Like Trail
Scientists have uncovered a new feature in one of the closest pulsars to
Earth, the Geminga pulsar. Plowing through space at 120 kilometers per
second (or Milan to New York City in 57 seconds), this dense nugget of a
dead star leaves in its wake a comet-like trail of high-energy electrons.
A team led by Dr. Patrizia Caraveo of the Italian National Institute for
Astrophysics (INAF) in Milan discovered this cometary trail with data from
NASA's Chandra X-ray Observatory Archive. The discovery follows the team's
discovery in 2003 using ESA's XMM-Newton of Geminga's twin X-ray tails
stretching for billions of chilometers.
Together, these observations provide unique insight into the contents and
density of the interstellar "ocean" Geminga is plowing through, as well as
the physics of Geminga itself. Not only is Geminga close, only about 500
light years from Earth, it is cutting across our line of sight, offering a
spectacular view of a pulsar in motion.
"Geminga is the only isolated pulsar we know of showing both a small
comet-like trail and a larger tail structure," said Dr. Andrea De Luca of
INAF's Istituto di Astrofisica Spaziale e Fisica Cosmica, lead author on
an article about this discovery in Astronomy & Astrophysics. "This
jettison from Geminga's journey through interstellar space provides
unprecedented information about the physics of pulsars."
A pulsar is a type of rapidly spinning neutron star that emits steady
pulses of radiation with each rotation, funnelled along strong magnetic
field lines, much like a lighthouse beam sweeping across space. A neutron
star is the core remains of an exploded star once at least eight times as
massive as the sun.
These dense stars, only about 20 kilometers across, still contain roughly
the mass of the sun. Neutron stars contain the densest material known.
Like many neutron stars, Geminga got a "kick" from the explosion that
created it and has been flying through space like a cannonball ever since.
De Luca said that Geminga's complex phenomenology of tails and a trail
must be from high-energy electrons escaping the pulsar magnetosphere
following paths clearly driven by the pulsar's motion in the interstellar
medium.
Most pulsars emit radio waves. Yet Geminga is "radio quiet" and was
discovered 30 years ago as a unique "gamma-ray only" source (only later
was Geminga seen in the X-ray and optical light wavebands). Geminga
generates gamma rays by accelerating electrons and positrons, a type of
antimatter, to high speeds as it spins like a dynamo four times per
second.
"Astronomers have known that only a fraction of these accelerated
particles produce gamma rays, and they have wondered what happens to the
remaining ones," said Caraveo, a co-author on the Astronomy & Astrophysics
article. "Thanks to the combined capabilities of Chandra and XMM-Newton,
we now know that such particles can escape. Once they reach the shock
front, created by the supersonic motion of the star, the particles lose
their energy radiating X-rays."
Meanwhile, an equal number of particles (with a different electric charge)
should move in the opposite direction, aiming back at the star. Indeed,
when they hit the star's crust they create tiny hotspots, which have been
detected through their varying X-ray emission.
The next generation of high-energy gamma-ray instruments -- namely, the
planned Italian Space Agency's AGILE mission and NASA's GLAST mission --
will explore the connection between the X-ray and gamma ray behaviour of
pulsars to provide clues to the nature of unknown gamma-ray sources,
according to Prof. Giovanni Bignami, a co-author and director of the
Centre d'Etude Spatiale des Rayonnements (CESR) in Toulouse, France. Of
the 271 higher-energy gamma-ray objects detected by a NASA telescope
called EGRET, 170 remained unidentified in other wavebands. These
unidentified objects could be "gamma-ray pulsars" like Geminga, whose
optical and X-ray light might be visible only because of its nearness to
Earth.
Only about a dozen other radio-quiet isolated neutron stars are known, and
Geminga is the only one with tails and trails and copious gamma-ray
emission. Bignami named Geminga for "Gemini gamma-ray source" in 1973. In
his local Milan dialect, the name is a pun on "ghè minga," which means "it
is not there." Indeed, Geminga was unidentified in other wavelengths until
1993, twenty years after its discovery.
The discovery team also includes Drs. Fabio Mattana and Alberto Pellizzoni
of the INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica.
[NOTE: An image supporting this release is available at
http://www.inaf.it/comunicati_stampa/cs161205/xmm_chandra.jpg (324KB) ]