- 2803 - PULSARS - Magnetars, stars behaving badly? Pulsars and magnetars are stars behaving badly. But, they are still following the laws of physics. These are Neutron stars. When stars get so big, their gravity gets so intense, the electrons collapse into the nucleus of protons and the star’s core made only of neutrons becomes a “Neutron Star” only 12 miles in diameter.
--------------- 2803 - PULSARS - Magnetars, stars behaving badly?
- Neutron stars have tested Einstein's 90-year-old general theory of relativity through a series of some of its most stringent tests ever imagined. It passed the tests.
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- Radio observations show that a recently discovered binary “pulsar” is behaving in lockstep accordance with Einstein's theory of gravity in at least four different ways, including the emission of gravitational waves and bizarre effects that occur when massive objects slow down the passage of time.
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- The binary pulsar, known as “J0737–3039“, was discovered in late 2003 using the 64-meter Parkes radio telescope in Australia. Astronomers instantly recognized the importance of this system, because the two neutron stars are separated by only 500,000 miles, which is only about twice the Earth–Moon distance.
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- At that small distance, the two 1.3-solar-mass neutron stars whirl around each other at a breakneck 670,000 miles per hour, completing an orbit every 2.4 hours.
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- . General relativity predicts that two stars orbiting so closely will throw off gravitational waves which are “ripples in the fabric of space-time” generated by the motions of very massive objects.
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- The rotating stars will lose orbital energy and inch closer together. This system is doing exactly what Einstein's theory predicts. The orbit shrinks by 7 millimeters per day, which is exactly in accordance with general relativity equations.
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- The astronomers have also measured another change in the binary pulsar's orbit, and found it to be consistent with other the predictions of general relativity. The “periastron” ,the point in the two pulsars' orbit where they come closest, advances 17 degrees per year, which is the largest ever observed.
- These astronomers observed another strange prediction of general relativity that clocks will run slower when closer to a massive object. When one pulsar approaches its partner's intense gravitational field, its rotational period appears to slow down by as much as 0.38 millisecond.
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- When one pulsar passes behind the other and its signal travels through the warped space-time created by the foreground pulsar, it adds a 90 microsecond delay to the arrival of its signal. With its 88-degree angle, we are very fortunate to see this system almost perfectly edge-on
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- Pulsars are the collapsed cores of massive stars that exploded as supernovae. These stellar remnants rotate with extreme regularity, and their pulsed radio emission makes these dense objects virtually perfect clocks for measuring subtle gravitational effects.
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- Pulsars are unique neutron stars being among the most extreme objects in the Universe. They are formed when a massive star dies in a "supernova explosion" . During this dramatic event, the core of the star suddenly collapses under its own weight and the outer parts are violently ejected into surrounding space. The electrons collapse into the protons and the nucleus becomes a solid sphere of neutrons.
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- One of the best known examples is the Crab Nebula in the constellation Taurus (The Bull). This nebula is the gaseous remnant of a star that exploded in the year 1054 and also left behind the pulsar, which is a rotating neutron star.
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- A supernova explosion is a very complex event that is still not well understood. Nor is the structure of a neutron star known in any detail. It depends on the extreme properties of matter that has been compressed to incredibly high densities, far beyond the reach of physics experiments on Earth.
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- The ultimate fate of a neutron star is also unclear. From the observed rates of supernova explosions in other galaxies, it appears that several hundred million neutron stars must have formed in our own galaxy, the Milky Way. However, most of these are now invisible, having since long cooled down and become completely inactive while fading out of sight.
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- When there is no sign of the associated supernova remnant and it must therefore be at least 100,000 years "old". Unlike younger isolated neutron stars or neutron stars in binary stellar systems, known as “RX J1856.5-3754“, does not show any sign of activity whatsoever, such as variability or pulsations.
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- However the emission of X-rays indicates a very high temperature for the star. From the moment of their violent birth, neutron stars are thought to lose energy and to cool down continuously. But then, how can an old neutron star like this one be so hot?
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- One possible explanation is that some interstellar material, gas and dust grains, is being captured by its strong gravitational field. Such particles would fall freely towards the surface of the neutron star and arrive there with about half the speed of light.
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- Since the kinetic energy of these particles is proportionate to the second power of the velocity, (velocity squared), even small amounts of matter would deposit much energy upon impact, thereby heating the neutron star.
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- While the chances for this were slim, a detection of such spectral features would be a real break-through in the study of neutron stars. If present in the spectrum, they could for instance be used to measure directly the immense strength of the gravitational field on the surface, which expected to be about 10^ 12 times stronger than that on the surface of the Earth.
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- It might be possible to determine the gravitational redshift, a relativistic effect whereby the light quanta (photons) that are emitted from the surface lose about 20% of their energy as they escape from the neutron star. Their wavelength is consequently red-shifted by that amount.
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- Most likely, the strong radiation from the very hot surface of the neutron star is ionizing hydrogen atoms (separating them back into a proton and an electron) in the surroundings, a process that also takes place near very hot, normal stars. The observed emission is then produced when, at a later time, the protons and electrons again recombine into hydrogen atoms.
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- With the inferred hydrogen density near the neutron star, about one thousand years will elapse between the moment of ionization by the passing neutron star and the subsequent re-unification of a proton with an electron to form a hydrogen atom.
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- During this time, however, the fast-moving neutron star will have covered a substantial distance. For this reason, it is expected that much of the hydrogen emission will not be seen very close to the neutron star, but rather along its "recent" trajectory.
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- The shape of the trajectory cone is like that of a "bowshock" from a ship, plowing through water. Similarly shaped cones have been found around fast-moving radio pulsars and massive stars. However, for those objects, the bowshock forms because of a strong outflow of particles from the star or the pulsar’s "stellar wind", that collides with the interstellar matter.
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- At present, it is still uncertain whether the observed density of the surrounding interstellar matter is sufficient to heat the star to the observed temperature. It is possible that sometimes in the past the neutron star managed to collect more matter during its travel through interstellar space, was heated, and is now slowly cooling down. In another million years or so, it will become undetectable, until it happens to pass through another dense interstellar region. And so on...
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- These nuclear furnaces in the Sun and stars creates blistering heat and blinding light. Magnetism, however, plays no role in the fusion process that converts their mass to energy. However, recently, researchers have found that neutron stars, already among the all-time weirdest objects, can be wrapped in magnetic fields brawny enough to affect the rest of the universe.
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- The first hint of magnetic trouble arrived March 5, 1979, when a gamma-ray burst swept through the solar system at the speed of light. Radiation monitors aboard spacecraft near Venus and Earth suddenly went off scale.
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- The deadly torrent lasted for only one-fifth second, but in that eye blink, some mysterious object had given off twice the energy our Sun had emitted since the building of the Pyramids! Scientists could not explain the burst by any known phenomenon. Eventually, the culprit was narrowed down to an invisible neutron star in a neighboring galaxy.
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- All neutron stars are tiny. Maybe 12 miles in diameter. They’re among the few suns with a solid surface which is an indestructible, half-mile-thick crust floating atop a bizarre fluid of subatomic particles. Each apple seed-sized speck outweighs a loaded freight train.
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- A neutron star forms when a massive star collapses and sends supernova brilliance outward while its tiny remnant core implodes. That core, now a 12-mile-wide sun of its own, spins crazily, often hundreds of times a second. Such frenzied motion causes its magnetic field to wrap around itself, intensifying the field lines.
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- What’s new about all this is an indication that during the youth of a neutron star, its magnetic field can reach the strength of a thousand trillion gauss. (Earth’s magnetism is less than 1 gauss.) Such stars are now logically called magnetars.
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- Astronomers have now discovered 23 confirmed magnetars, but only one, in Cassiopeia, is visible through optical telescopes. Astronomers detected the others solely by the types of radiation they emit. The nearest is a less than 9,000 light-years away, and more than a million other unknown magnetars are thought to be unseen in the dusty hallways of our Milky Way.
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- The biggest magnetar that came on December 27, 2004 emitted more energy in a tenth of a second than our Sun has released in 100,000 years! If it were located within 10 light-years of us, it would have obliterated our planet’s ozone layer and caused mass extinction. That includes you and me.
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- The magnetar source is utterly invisible in visible light. It lurks directly behind the center of our galaxy, on the opposite side of the Milky Way, some 50,000 light-years away. Its name is “SGR 1806–20“. This object in the constellation Sagittarius is the most magnetic object ever perceived.
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- The 2004 burst changed our ionosphere from night to day. Some fishermen in the arctic saw a sudden aurora at that moment.
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- Magnetars have a unique source of power. All of its energy comes from the gradual loss of its magnetic field.” The intense magnetism bends and deforms a magnetar’s solid crust to produce “starquakes.”
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- These starquakes are nothing like the tremors we get here, which can merely destroy a city. A neutron star’s ultra-dense starquakes release titanic bursts of energy that actually create electrons and antimatter positrons. When those combine and annihilate each other, they produce the lethal gamma rays that sweep through the universe.
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- This intense magnetism slows the star‘s rotation. In a mere 10,000 years the magnetic field weakens to a only 2 trillion times greater than Earth’s. Then, the starquakes stop and the gamma rays die out.
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- These magnetars embody the physics of extremes: density, gravity, and magnetism. At 2,000 miles distance the magnetar still appears as just a pinpoint, but its magnetism pulls every group of atoms into long, strange, needle formations.
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- Now, tell me, astronomy is not interesting? Even amazing beyond your imagination?
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- August 27, 2020 2803
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