- 3071 - STARS - neutron stars, magnetars and pulsars? Big stars have short lives and dramatic deaths. This review highlights the bigger supernovae explosions that create Gamma Ray Bursts, Magnetars, and Pulsars. It refers to a small satellite student project that hopes to contribute to our understanding of these cosmic wonders.
--------------------- 3071 - STARS - neutron stars, magnetars and pulsars?
- Stars come in all sizes. Big stars were the first stars created after the Big Bang. Big stars have short lives, maybe only 1 million years before they burn all their fuel because they burn so brightly with their gravity so immense..
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- Small stars like are Sun do not burn so bright and their fuels last 1,000 times longer, maybe 10,000,000,000 years. The mass of our Sun can be used as the standard mass, one “Solar Mass“, or, “Ms“, to compare with other stars. Big stars have 50*Ms and there are all sizes of stars in between.
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- When a big star ends its life after 1 million years it has burned through the fusion of all the elements up to iron. The elements start with hydrogen ( 1 proton ), then Helium (2 protons), … all the way up to iron ( 26 protons ) in the Periodic Table.
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- Each element created in the fusion process occupies an onion shell in the star from the core up to the surface. When the core is all iron, fusion stops. Iron is the heaviest element that releases energy when it fuses.
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- The next heavier element heavier than iron requires the “addition of energy” in order to fuse. If fusion no longer releases energy to create the radiation pressure holding back gravity, the star collapses.
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- Each element in our Sun and in other stars creates elements that have slightly less mass than their component parts, lighter elements. The extra mass is converted into energy in the form of Gamma Ray radiation. It is the outward pressure of the escaping radiation that balances against the inward pressure of gravity.
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- When the fusion stops the radiation stops and gravity wins. The star collapses. The collapsing star meets at the core and rebounds in a supernovae explosion. A 50*Ms star will explode sending off 48*Ms of its mass into the interstellar medium.
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- The resulting shockwave will fuse heavier elements that require higher energy absorption in order to fuse. All the natural elements in the Periodic Table get scattered into space as gas and dust in this process. The next generation of stars will be crated out of this same gas and dust.
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- So what happens to the 4% of this star that remains at the core as the remnant after the explosion? 2*Ms is left at the core. There is no radiation left to fight the further collapse from the pressure of gravity. However, there is one counteracting pressure next in line. It is the “electromagnetic pressure” between the electron and the nuclei of the atoms.
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- The electron refuses to collapse preventing gravity from winning once more. A balance is struck only as long as the mass is less than 1.4*Ms. The star that remains in this balance is called a “White Dwarf“. This is what our Sun, 1.0*Ms, will become after it burns all its fuel in another 5 billion years. You’ll have to tell me about it.
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- If the mass of the remnant star is greater than 1.4*Ms then the electron’s pressure can no longer overcome the collapsing pressure of gravity. The electrons collapse into the protons in the atomic nuclei creating neutrons at the core. The core collapses into a “Neutron Star” that is about 12 miles in diameter and contains a mass 40% greater than our Sun.
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- If the star is 30 to 40*Ms the Neutron Star is likely to become a “Magnetar” living 6,000,000 years.
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- If the star is up to 8 to 30*Ms the Neutron Star may become a “Pulsar” beaming radio waves and living for 1,000,000,000 years.
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- If the mass and gravity of an exploded star remains greater than 8*Ms then even the neutron pressure can not prevent further collapse. The Neutron Star will collapse into a Blackhole.
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- It all depends on the mass of the star and the mass that is left over after the supernova explosion. No two supernova explosions or planetary nebulae are alike. They are like snowflakes, every one is different when you look closely. There are millions of Neutron Stars in the Milky Way Galaxy.
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- When a star greater than 8*Ms explodes in a supernova what remains often collapses into a Neutron Star. The Neutron Stars that are left behind can all behave differently depending on the energy that is left behind with them.
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- Some Neutron Stars become Magnetars exhibiting magnetic fields of unbelievable strength. If a Magnetar star flew between Earth and the Moon, 100,000 miles from us, it would wipe clean every credit card on the planet. It would slow to a stop any steel locomotive. The first Magnetar was discovered in 1998. We have since discovered 12 Magnetars so far in the Milky Way Galaxy.
- If the Neutron Star is less energy it may become a Pulsar beaming radio waves. Its spinning rotation of the star will flash the radio beam at us several times each second. We have discovered about 1,500 Pulsars in the Milky Way Galaxy.
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- Magnetars flash X-ray beams at a much slower rate, every 10 seconds or so with an occasional burst of Gamma Rays. Magnetars have slower rotations because their magnetic fields are slowing them down.
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- Astronomers measure a Magnetar’s magnetic power by measuring how fast the star’s spin is slowing down. A rotating magnetic field radiates off energy. The energy loss results in a decelerating of the star’s rate of rotation. After 10,000 years or so the rotation becomes slow enough that the X-ray beam is turned off and the star remaining becomes a Pulsar.
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- Astronomers use another measure of a Magnetar’s power. An empty bubble surrounds a Magnetar implying a solar wind that is 25,000,000 times greater than our Sun’s solar wind.
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--------------------Magnetar = 44,000,000,000,000 Gauss
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------------------- Refrigerator Magnet = 100 Gauss
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------------------ Earth’s magnetic field = 0.6 Gauss
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- Magnetars have a crust that is 1 mile thick made of iron nuclei packed into a crystalline lattice. The star is rapidly spinning with a 12 mile diameter while containing an enormous mass in such a small space. It has as much as 140% the mass of the Sun.
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- The crust of the Magnetar can experience “star quakes” that buckle the crust releasing flares of tremendous energy. The explosion can set the entire star ringing like a bell. Vibrations of 200 to 400 cycles per second are about middle C on the piano.
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- It is thought that the interior of a Neutron Star might be so dense as to harbor only Quarks and Leptons, fundamental particles that make up the nucleus of atoms. This would be a “Quarkstar” if it is ever discovered to exist. Quarkstars might be compressed to only 7 miles diameter and have core temperatures of 1,000,000 degrees.
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- There is a Neutron Star heading toward us now and only 200 lightyears away. It will pass Earth in 300,000 years from now and only miss us by 170 lightyears.
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- So far 6 of the Neutron Stars have been discovered as binaries. Two Neutron Stars orbiting each other around a common center of gravity. These orbits will eventually decay and the Neutron Stars will collide collapsing into a Blackhole.
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- Why do the orbits decay? The theory is because their enormous rotating masses are radiating gravitational waves. Astronomers have just recently began detecting these gravity waves.
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- There is a particular pair of binary Neutron Stars that are 500,000 miles apart orbiting each other every 2.4 hours. As their orbits decay the frequency of rotation will increase to 30 cycles per second, then 1,000 cycles per second, then collision and collapse into a Blackhole. ( See Review “LIGO - Laser Interferometer Gravitational Wave Observatory”)
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- If the star is 50*Ms then its collapse may likely go directly into a Blackhole releasing an enormous amount of energy in the form of a Gamma Ray Burst. A single burst lasting 1/10 of a second can release more energy than the Sun will release over 100,000 years.
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- December 27,2009, a powerful Gamma Ray Bust struck Earth. It originated from a Neutron Star collapsing 50,000 light years away. If you could see Gamma Rays it would have appeared brighter than a Full Moon. This blast of radiation was 100 times greater than astronomers have every recorded before.
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- The Gamma Rays hit the Earth’s ionosphere creating ionization of the gases and expanding of the entire sphere. The Sun is only 8 lightminutes away, not 50,000 lightyears away, so the effect of Solar Flares is much greater. We were just lucky that this Gamma Ray flare took 50,000 lightyears to reach us.
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- Gamma Ray Bursts are supernovae of massive stars that have very different properties. Intense narrow jets of hot plasma are blasted out the rotational axis. If one of the jets are pointed toward us we see a Gamma Ray Burst. The beam is believed to be created, or, contained by a powerful rotating spiraling magnetic field.
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- It is likely that a Blackhole is creating these bursts and not a Neutron Star. Observations of 4 Gamma Ray Bursts have concluded that they are too powerful to be created by a Magnetar.
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- Astronomers must leap to a more powerful energy stage, a Blackhole. But, how? As so often happens conclusions are theoretical vapor until more hard data is observed. There is a student project at Berkeley University that proposes launching a small satellite to get some needed hard data.
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- Supernovae are not well understood. What causes the explosion? A simple rebound is not enough to explain the escaping energy. Could it be neutrinos that are carrying away the enormous energy? Could it be sound waves? So far computer models simulating supernovae with our existing understanding of physics will not reproduce what we observe. We need to learn more.
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- Project “Polosat“, a small satellite the size of a wash tub that will detect the Gamma Ray polarization of these bursts. If the theory of spiraling magnetic fields is what is creating these powerful bursts then they should discover circular polarization looking directly at the beam and linear polarization of the light that is 10 to 15 degrees off the beam axis.
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- If the light is not polarized then something else is causing the Gamma Ray beams. Data on Gamma Ray polarization will be a significant leap in our understanding of what is creating Gamma Ray Bursts that are occurring once every day on average.
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- There is another student small satellite project at UC Berkeley. It is a satellite to be launched to study the “albedo” of the Earth. The albedo is the amount of radiation that the Earth reflects back into space. The satellite will make these measurements by reading the Earthshine on the Moon.
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- In a crescent Moon the darker portion is still lighter by the reflected light from the Earth. Measuring this over 10 to 30 years will tell science if the Earth is absorbing more radiation or reflecting more radiation over time. Is there global warming?
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- This data is what the environmentalist are needing to prove that the Earth is warming up, reflecting less of the energy that is incident on it from the Sun would mean the Earth is absorbing more energy in greenhouse gases..
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- The albedo of the Moon is 6.8%. The albedo of the Earth is about 30%. That is, the Earth reflects 30% of the sunlight that hits it. But, how is that varying over time? Project “Danjon” will tell us and it is all run and operated by students.
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- Stay tuned we may be announcing some Noble Prizes to Berkeley students in the years ahead. Wouldn’t that be great?
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March 1, 2021 STARS - neutron stars, magnetars, pulsars? 1223 3071
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--------------------- --- Tuesday, March 2, 2021 ---------------------------
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