-
2156 - Magnetars and pulsars belong to a class of
objects called neutron stars, which are big balls of tightly packed neutrons no
larger than a big city. When stars above
about eight solar masses run out of fuel to burn, they explode in what is
called a supernova. What remains can collapses into a neutron star.
-
-
-
---------------------------------- 2156 - Magnetars and pulsars
-
- Magnetars and
pulsars belong to a class of objects called neutron stars, which are big balls
of tightly packed neutrons no larger than a big city. When stars above about eight solar masses run
out of fuel to burn, they explode in what is called a supernova. What remains
can collapses into a neutron star.
-
- Pulsars are
dead stars that have burned up their hydrogen and helium and collapsed into
themselves at a core of neutrons. They become
pulsars because when they collapse they maintain their conservation of angular
momentum spinning at incredible speeds, thousands of revolutions per
minute. At their poles they spew out intense
beams of radio waves and X-rays.
-
- Magnetars have
close cousins called pulsars. Pulsars
are stellar corpses that serve as the radio lighthouses of the galaxy. Spinning
around several times a second, they flash the galaxy with a beam of radio
waves. Magnetars are similar, but they
flash X-rays, and at a slower rate, about once every 10 seconds. They also
occasionally let out a burst of gamma rays.
-
- There are
about 1,500 known pulsars, but less than a dozen firmly identified magnetars.
What makes magnetars special is their magnetic field, which is thousands of
times stronger than that of normal pulsars and billions of times stronger than that
of any magnet on Earth.
-
- These
magnetic fields can be measured by observing how quickly the spin of the
magnetar slows down. A rotating magnet gives off energy, and the greater the
magnetic field, the faster the energy loss. Magnetars exhibit rapid
deceleration, which implies a huge magnetic field. After 10,000 years a magnetar will slow down
enough to totally turn off its X-ray flash.
-
- It takes a
very massive star, some 30 to 40 solar masses to produce a magnetar. This progenitor star lives 5-6 million years
before it explodes , creating the magnetar in its ashes. Massive stars die
young. Our middle-ages Sun, by comparison, is about 4.6 billion years old, and will
live another 4.5 billion years.
-
- Astronomers
used to think that really massive stars formed black holes when they died. But in the past few years we've realized that
some of these stars form pulsars rather than blackholes, because they go on a
rapid weight-loss program before they explode as supernovae.
-
- At the very
end of its life, the star likely lost 90 percent of its mass, which would make
it skinny enough to become a neutron star, as opposed to a black hole.
-
- In our galaxy
there are only about 10 neutron stars that are massive enough and at the right
age to be magnetars right now. There could be many more "dead"
magnetars already in the galaxy, however.
-
- Observations
of "starquakes" have allowed scientists to estimate the thickness of
a neutron star's crust for the first time.
Neutron stars are very dense objects that mark the endpoints of the
lives of some stars. Using a technique
similar to seismology here on Earth, researchers estimated that the crust of a
highly magnetic neutron star, a "magnetar," is nearly 1 mile thick
and made of material so tightly packed that a teaspoonful of the stuff would
weigh about 10 million tons on Earth.
-
- A neutron
star forms when an ancient star several times more massive than our Sun runs
through its entire stock of nuclear fuel. The star collapses under the weight
of its own gravity and explodes in a cataclysmic event called a supernova. The blast ejects most of the star's mass into
space, leaving behind a dense, rapidly spinning core about the size of a small
city and roughly 1.4 times more massive than our Sun.
-
- Magnetar's
are neutron stars whose magnetic fields are thousands of times stronger. Astronomers
have detected only about a dozen such stars. A magnetar's magnetic field is
equivalent to about a hundred trillion refrigerator magnets and so strong that
it could slow a steel locomotive from as far away as the Moon.
-
- The flash
resulting from a violent explosion called a "hyperflare," occurs when
a magnetar's magnetic field lines become so twisted with one another that they
snap. Like a tightly wound rubber band that finally breaks, the snapping
releases tremendous amounts of energy, triggering a "starquake" that
buckles the star's crust.
-
- Astronomers
calculate the thickness of the magnetar's crust by comparing the frequencies of
energy waves traveling around the star against those passing through its
interior.
-
- The interior
of neutron stars has been a source of great mystery and speculation for
scientists. The pressure and density inside a neutron star core is thought to
be so great that it could harbor exotic particles called quarks not found since
the moment of the Big Bang.
-
- The stars'
interiors could contain these quarks which are the building blocks for protons
and neutrons. Even the most powerful particle accelerators on Earth can't
muster up the energies needed to reveal free quarks.
-
- Astronomers
have discovered two neutron stars orbiting each other once every 2.4 hours and
spiraling inward toward an eventual dramatic collision. The finding suggest
such intense events are far more common than was thought. Astronomers hope to detect elusive
"gravitational waves," which should be spawned in the final seconds
prior to binary neutron star mergers.
-
- A neutron
star is already a stellar corpse. It is formed when an aged star explodes and
as much material as what's in our Sun collapses into a region the size of a
city. A teaspoonful, brought to Earth, would weigh a billion tons or so.
Neutron stars are stuffed almost entirely with neutrons, neutral subatomic
particles that can huddle extremely close together.
-
- Only six
neutron-star pairs, called binary systems, are now known. Previous studies of other pairs have shown
that these exotic dance teams spiral toward each other and must eventually
crash and unite, possibly becoming a blackhole. Einstein theorized that space-warping
gravitational waves, caused by two accelerated masses in orbit, are the reason
for this orbital decay.
-
- As Einstein's
theory has it, any pair of neutron stars should begin a detectable death chirp
moments before they merge. One minute
before the stars merge, their orbit has shrunk to a size of only a few hundred
miles, and the two neutron stars move around each other some 30 times each
second, producing strong gravitational waves with that same frequency of 30 cycles per second.
-
- In the last
minute before the merger, the orbital frequency increases rapidly, from 30 to
1,000 times per second. The strength of
the gravitational wave emission increases simultaneously.
When the waves reach Earth, their effect would be to
displace the oceans by an amount roughly 10 times the diameter of an atomic
nucleus. That is too small to notice on an ocean liner.
-
- There are
several projects around the world designed to detect these otherwise unnoticed
waves. Among the most prominent is the Laser Interferometer Gravitational Wave
Observatory (LIGO).
-
- The
observatories must be very sensitive. Gravitational waves are said to be
similar to light waves. Both propagate through space at different frequencies,
radiating outward like ripples on a pond. But gravitational radiation is much
weaker than electromagnetic radiation, which includes light, radio waves and
X-rays. This is because the fundamental force of gravity is weaker than the
fundamental electromagnetic force.
-
- The Sun is a
middle-aged star about 8 light-minutes from us. Its tantrums, though extremely small
compared to the magnetar explosion, routinely squish Earth's protective magnetic
field and alter our atmosphere, lighting up the northern night sky with
colorful lights called aurora.
-
- Solar storms
also alter the shape of Earth's ionosphere, a region of the atmosphere 50 miles
up where gas is so thin that electrons can be stripped from atoms and molecules
become ionized and roam free for short periods. Fluctuations in solar storm
radiation cause the ionosphere to expand and contract.
-
- A neutron
star is the remnant of a star that was once several times more massive than the
Sun. When their nuclear fuel is depleted, they explode as a supernova. The
remaining dense core is slightly more massive than the Sun but has a diameter
typically no more than 12 miles.
-
- Millions of
neutron stars fill the Milky Way galaxy. A dozen or so are ultra-magnetic
neutron stars, magnetars. The magnetic field around one is about 1,000 trillion
gauss, strong enough to strip information from a credit card at a distance
halfway to the Moon.
-
- When massive
stars go supernova they produce a magnificent nebula. But if the star is not massive
enough to produce a blackhole, it usually leaves behind a neutron star.
-
- A neutron star
crams as much mass as our Sun into a sphere just 10 miles across. Squeezing out
the empty space that makes up most of the Sun's volume, neutron stars leave only
naked atomic nuclei.
-
- This cosmic neutron
star rotates and has an intense magnetic field and a thin crust of iron nuclei
packed into a crystalline lattice . At about 44 trillion gauss, the magnetic
field is 1,000 times stronger than that of an ordinary neutron star. By
comparison, the Earth's magnetic field is a tame 0.6 gauss, and a refrigerator
magnet, a feeble 100 gauss.
-
- The most a
human being can normally expect to be exposed to in his life is about 100,000
gauss from a magnetic resonance imager MRI.
A field of 1 billion gauss would turn you into magnetized mush.
-
- Since the
star's magnetic field is a drag on rotation, it slows the rotation. The losses
are almost imperceptible, about 1 part in 100 billion. But that represents a lot of energy since
it's braking such a compact yet massive object. In the span of about 10,000
years it slows down to become an X-ray
Pulsar. Only six of these are known to date.
-
- Under the
magnetar theory however, one way that energy is released is when the
diamond-like crust suddenly cracks, shifting and pumping energy into the
ionized gases trapped around the magnetar. The result of the starquake arrives at Earth
as brilliant gamma-ray flares. On Aug. 27, 1998, such an outburst ionized as
much of the Earth's outer atmosphere as the Sun would at high noon.
-
- Quarks are
thought to be fundamental building blocks of matter. But they have never been
observed alone, instead always existing together as the components of other
matter. If they were liberated inside a star, they could theoretically be
compressed into a smaller sphere.
-
- Massive,
dying stars vibrate like giant speakers and emit an audible hum before
exploding in one of nature's most spectacular blasts. A new model developed suggests that sound
waves, not ghostly particles called neutrinos, deal the final blow to stars
before they become supernovas.
-
- Supernovae
are powerful stellar blasts that briefly outshine entire galaxies and radiate
more energy than our Sun will in its entire lifetime. Only a star that is
between 10 to 25 times more massive than our Sun can become a supernova. After
it has burned for 10 to 20 million years or so, the star runs out of fuel and
develops a dense iron core about the size of Earth.
-
- The iron core
grows until its density becomes so great that it collapses under its own
weight. The core contracts, but then almost immediately springs back again.
This sudden rebounding action generates a shockwave that speeds outward. It is this departing shockwave that triggers
the supernova explosion.
-
- The problem,
however, is that in even the best computer simulations, the shock wave isn't
powerful enough on its own to break through the dense layers of superheated gas
that envelops the core. In the models,
the shock wave stalls as if muffled by a blanket and the supernova explosion
never occurs.
-
- Astronomers
began experimenting with the idea that ghostly subatomic particles known as neutrinos
might provide the extra power boost needed to complete the blast. Neutrinos have no charge and are nearly
massless. They are produced in vast quantities during the final stages of a
massive star's life and stream out of the star's inner core. It was thought
that these escaping particles might carry enough energy out of the core to the
star's outer layers to complete the explosion.
-
- But even when
scientists incorporated the outflow of neutrinos into their computer
simulations, it still wasn't enough to produce consistent supernovas.
-
- Instead of
neutrino's heating up the material behind the shock, maybe acoustic power could be doing it. The
material on the inside is oscillating like a very, very strong speaker and
sending out energy via sound. The
vibrations become so energetic that they create sound waves with audible
frequencies in the range of 200 to 400 hertz, or around middle C.
-
- In this scenario, the sound waves replace
neutrinos as energy carriers. The sound
waves propagate out through the material and heat it up. It acts in a way similar to the way neutrinos
would act but with more efficiency.
-
- Pulsars were
first discovered in 1967 by Bell Burnell
who strung 120 miles of wire to create a 4.5 acre radio telescope in Cambridge
, England. His "instrument"
detected a radio signal barely rising above the background noise on his
recordings.
-
- Further study
found the same signal in 10 percent of his recordings arriving 4 minutes
earlier each day. These precisely timed
radio signals were 1.3373 seconds apart.
Stars could not change brightness that quickly. The source had to be an unfathomably dense,
small object.
-
- Today we know the source to be two orbiting neutron
stars whirling around each other every 7.75 hours. Their orbits are shrinking by 3.2 millimeters
per circuit as they loose energy to radiating gravitational waves.
The two neutron stars are scheduled to collide in just 300,000,000
years.
----------------------------------------------
- Other Reviews available on pulsars and
magnetars:
-
- 1431 - Pulsar
motion is being observed to learn if gravity behaves differently around Neutron
stars. Will gravity waves move the
pulsars with the passing wave?
-
- 1397 -
Ordinary Matter should be called Ordinary Space. The matter part is almost negligible. Almost all of solid matter is empty
space. It is not solid at all. What makes it feel solid is the
electromagnetic force.
-
- 1396 - High
school students discover a Pulsar.
-
- 1376 - How can Pulsars have planets? The Earth as the first planet to be
discovered. And, it just happens to be
the right size, the right temperature, and orbiting the right star. How lucky can you get? Math: How to calculate the distance to a
star.
-
- 1331 - How
Neutron Stars become Pulsars? Eight
supernovae explosions have been recorded witnessed by human naked eyes. Spin rates of pulsars slow down as the drag
of the strong magnetic field causes a loss of spin energy.
-
- 1327 - The
fastest spinning star? The neutron stars
is spinning so fast it would fly apart except for the fact that its surface is
solid and harder than a diamond. Math: If
the neutron star has a radius of 10 kilometers and is spinning at 716 rotations
per second how big was it when it started?
-
- November 8, 2018.
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------ “Jim Detrick” -----------
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--------------------- Thursday, November 08, 2018 -------------------------
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