3809
- MAGNETIC STAR - X-ray
telescopes new discoveries? Launched on
December 9, 2021, IXPE is the first satellite that can measure the polarization
of X-ray light with this level of sensitivity and clarity. It was designed to
discover the secrets of some of the most extreme objects in the universe the
remnants of supernova explosions, powerful particle streams spit out by feeding
black holes.
--------- 3809 - MAGNETIC STAR - X-ray telescopes new discoveries?
- The X-ray light emitted by a certain
“magnetar”, a highly magnetized dead star, indicates that this star has a solid
surface and no atmosphere.
-
- The “Imaging X-ray Polarimetry Explorer”
(IXPE) satellite reveals that a highly magnetized dead star known as a magnetar
has a solid surface with no atmosphere.
This represents the first time polarized X-ray light from a magnetar has
been observed.
-
- “IXPE” allows scientists to examine
X-ray light in space by measuring its polarization, the direction of the light
waves’ oscillation. The magnetar
“4U 0142+61”, located in the Cassiopeia constellation is 13,000 light
years from Earth.
-
- Magnetars are neutron stars which are
very dense remnant cores of massive stars that have exploded as supernovae at
the ends of their lives. Unlike other neutron stars, they have an immense
magnetic field, the most powerful in the universe.
-
- Magnetars emit bright X-rays and show
erratic periods of activity, with the emission of bursts and flares which can
release in just one second an amount of energy millions of times greater than
our Sun emits in one year. They are believed to be powered by their
ultra-powerful magnetic fields, 100 to 1,000 times stronger than standard
neutron stars.
-
- They found a much lower proportion of
polarized light than would be expected if the X-rays passed through an
atmosphere. Polarized light is light
where the wiggle is all in the same direction, the electric fields vibrate only
in one way. An atmosphere acts as a filter, selecting only one polarization
state of the light.
-
- The team also found that for particles
of light at higher energies, the angle of polarization, flipped by exactly 90
degrees compared to light at lower energies, following what theoretical models
would predict if the star had a solid crust surrounded by an external
magnetosphere filled with electric currents.
-
- But, like with water, temperature is also a
factor, a hotter gas will require a stronger magnetic field to become solid. The most exciting feature they could observe
is the change in polarization direction with energy, with the polarization
angle swinging by exactly 90 degrees.
-
- Quantum theory predicts that light
propagating in a strongly magnetized environment is polarized in two
directions, parallel and perpendicular to the magnetic field. The amount and
direction of the observed polarization bear the imprint of the magnetic field
structure and of the physical state of matter in the vicinity of the neutron
star.
-
- At high energies, photons (particles of
light) polarized perpendicularly to the magnetic field are expected to
dominate, resulting in the observed 90-degree polarization swing.
-
- The polarization at low energies is
telling us that the magnetic field is likely so strong to turn the atmosphere
around the star into a solid or a liquid, a phenomenon known as “magnetic
condensation”.
-
- The solid crust of the star is thought
to be composed of a lattice of ions, held together by the magnetic field. The
atoms would not be spherical but elongated in the direction of the magnetic
field.
-
- It is still a subject of debate whether
or not magnetars and other neutron stars have atmosphere.
-
- The “Imaging X-ray Polarimetry Explorer”
has measured and mapped polarized X-rays from the remains of this exploded
star. The findings come from observations of Cassiopeia A, a famous stellar
remnant. The results shed new light on the nature of young supernova remnants,
which accelerate particles close to the speed of light.
-
- All forms of light, from radio waves to
gamma rays, can be polarized. Unlike the polarized sunglasses we use to cut the
glare from sunlight bouncing off a wet road or windshield, IXPE’s detectors map
the tracks of incoming X-ray light. Scientists can use these individual track
records to figure out the polarization, which tells the story of what the
X-rays went through.
-
- Cassiopeia A was the first object IXPE
observed after it began collecting data. One of the reasons “Cas A” was
selected is that its shock waves, like a sonic boom generated by a jet, are
some of the fastest in the Milky Way. The shock waves were generated by the
supernova explosion that destroyed a massive star after it collapsed. Light
from the blast swept past Earth more than three hundred years ago.
-
- Magnetic fields, which are invisible,
push and pull on moving charged particles like protons and electrons. In an exploding star, magnetic fields can
boost these particles to near-light-speed.
-
- Despite their super-fast speeds,
particles swept up by shock waves in Cas A do not fly away from the supernova
remnant because they are trapped by magnetic fields in the wake of the shocks.
The particles are forced to spiral around the magnetic field lines, and the
electrons give off an intense kind of light called “synchrotron radiation,”
which is polarized.
-
- By studying the polarization of this
light, scientists can “reverse engineer” what’s happening inside Cas A at very
small scales, The angle of polarization tells us about the direction of these
magnetic fields. If the magnetic fields close to the shock fronts are very
tangled, the chaotic mix of radiation from regions with different magnetic
field directions will give off a smaller amount of polarization.
-
- Previous studies of Cas A with radio
telescopes have shown that the radio synchrotron radiation is produced in
regions across almost the entire supernova remnant. Astronomers found that only
a small amount of the radio waves were polarized, about 5%. They also determined
that the magnetic field is oriented radially, like the spokes of a wheel,
spreading out from near the center of the remnant towards the edge.
-
- Data from NASA’s Chandra X-ray
Observatory, on the other hand, show that the X-ray synchrotron radiation mainly
comes from thin regions along the shocks, near the circular outer rim of the
remnant, where the magnetic fields were predicted to align with the shocks.
-
- Chandra and IXPE use different kinds of
detectors and have different levels of angular resolution, or sharpness.
Launched in 1999, Chandra’s first science image was also of Cas A.
-
- Cassiopeia A is the remnant of a
supernova explosion that appeared in our sky more than 300 years ago. It is
located a distance of approximately 11,000 light years from Earth. Its name is
taken from the constellation in which it is seen, Cassiopeia, the Queen.
-
- A supernova is the cataclysmic explosion
that occurs at the end of a massive star’s life. Cas A is the expanding shell
of material that remains from such an explosion.
-
January 1, 2022 3804
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--------------------- --- Thursday, January 5, 2023 ---------------------------
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