- 3581 - GAMMA RAYS - where do they come from? To create Gamma Rays you need a lot of energy. Energy that comes from colliding particles at near the speed of light. Or, from the annihilation of matter and anti-matter, accretion disks and jets around Blackholes, or radioactive decay in fusion reactors.
--------------------- 3581 - GAMMA RAYS - where do they come from?
- Gamma Rays are light of the maximum possible energy. With wavelengths shorter than 10^-11 meters, each Gamma Ray photon has an energy of at least 100,000 electron volts. That is 100,000 times more energy than visible light.
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- Some Gamma Rays have even shorter wavelengths and even more energy. The most energetic Gamma Ray recorded was 100,000,000,000 electron volts.
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- Sunlight at the core of the Sun starts out as Gamma Rays and loses energy as it passes through layers and layers of gas. It leaves the surface as ultraviolet and visible light.
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- When a massive star blows up as a supernova it emits Gamma Rays. Some Gamma Ray bursts are so intense they can outshine 100,000,000 galaxies. If astronomers want to see a distant galaxy that is far, far away, a Gamma Ray Burster is the one to catch.
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- Astronomers want the farthest distances to go back farther in time. They are looking for a redshift of 10 which corresponds to the age of the Universe at 500,000,000 years, 3.6% its current age, which is 13,800,000,000 years After catching some 60 long bursts they have recorded only one with a redshift greater than 6.
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- Short duration Gamma-Ray Bursts are believed to be the result of 2 colliding neutron stars. The bursts last only a fraction of a second in these situations.
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- Long duration bursts last tens of seconds. These typically lie at a much greater distance when the age of the Universe was only a few billion years old. Long duration bursts are believed to be massive supernova that become rapidly spinning Blackholes. These events can become intensely magnetized neutron stars called Magnetars.
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- The bursts are short lived but the afterglows can last for days. Powerful jets pour out of the supernova heating the gas that surrounds the star. This creates the optical and radio waves that continue to radiate energy.
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- One Gamma Ray Burst was detected with a redshift of 6.295 when the age of the Universe was 900,000,000 years old. The expansion of the Universe over time makes the Burst appear to last longer because the radiation is stretch out and also stretched to longer wavelengths. High energy X-rays can become stretched into the infrared wavelengths. The optical wavelengths are missing because the intergalactic clouds of neutral hydrogen have absorbed all the visible light along the way.
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- The afterglow of the Gamma Ray Burst starts out about one lightyear distant from the supernova. It passes through the host galaxy and then through billions of lightyears of interstellar medium to reach the Earth. The light we observe can contain fingerprints of the interstellar gas and dust it has encountered.
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- The spectroscopy data on this light shows absorption lines for the atoms and elements the light passed through. One conclusion reached is that these distant galaxies contain less than 10% of the heavy elements that we find today in the Milky Way.
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- Astronomers need more Infrared telescopes in order to see these most distant Gamma Ray Bursts. Analyzing these Gamma Ray Bursts is like culling a line of sight through the Universe that could map out evolution in 3 dimensions. With many lines of sight recorded a detailed picture begins to form.
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- Astronomers are just beginning to see in Gamma Rays. Visible light has energies between 2 and 3 electron volts. An electron volt is the energy of a single electron moving through a voltage about the potential of a flashlight battery. A very small amount of energy. Gamma Rays are light photons of very high energy, in the 100,000 to 100,000,000 electron volts.
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- Astronomers now have telescopes in space that can see in Gamma Rays. They can see radiation coming from all directions in bursts of Gamma Rays at the rate of one detection per day. These “spots of light“, or Gamma Ray beams, seem to be random and every where in the Universe. Because they are so bright in energy they can be seen over very large distances, billions of lightyears away.
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- Astronomers are studying the sources for Gamma Rays and they have given objects several different names, Gamma Ray Bursts, Pulsars, Magnetars, Blazars, flares from massive Blackholes, annihilation of matter and anti-matter.
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- The exact physics for these different Gamma Ray sources is still being worked out. The wavelengths they are detecting are a few trillionths of a meter, the size of an atom. When the detectors are set to record every Gamma Ray photon over 300,000,000 electron volts over a year’s period the detector’s image completely lights up the entire Milky Way.
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- Gamma Ray Bursts have been observed to outshine everything else in the Universe. The Bursts can last up to 25 seconds. 90 minutes after the Bursts there is an afterglow that is a trillion times brighter than our Sun.
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- For example, a particular Burst was 2.65 billion lightyears away. The nearest any long term Burst has been recorded was 140 million lightyears away. So, most Bursts are occurring in the very early Universe like this one.
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- The expansion rate of the supernova remnant was measured to be 22,000 miles per second, or 79,200,000 miles per hour. The burst was believed to be the result of jets of particles shot out of the poles of a massive exploding supernova. We are only seeing the Bursts when the jets are pointed directly at us. So, for every one we see, about one per day, there are some 300 Bursts that we do not see.
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- The Bursts are coming from super massive stars, greater than 20 Solar Mass. These stars have surface temperatures of 50,000 Kelvin. They emit stellar winds at 900 miles per second, or 3,240,000 miles per hour.
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- The stellar winds can reduce the mass of the star to 1/3 its original mass before it goes supernova. A star that began with a 35 solar mass ends its life at 10.6 Solar Mass. A super massive star will burn through its nuclear fuel very rapidly.
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- A star 5.5 million year old will have depleted all of its hydrogen fuel. Then it begins burning helium, then carbon, then oxygen, then neon, then silicon, then the core is left with the element iron-nickel. At that point the fusion stops and the star explodes as a supernova.
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- When the star dies its radius is 560,000 miles. 10.6 Solar Mass of hydrogen has been blown away. The rest of the star is layered like an onion. The Core is iron, 1.5 Solar Mass and 900 miles radius.
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- The mass and radius of the other layers are in the table below:
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------------------ iron --------------------- 1.5 Solar Mass ------------- 900 miles
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------------------ silicon ------------------ 0.2 Solar Mass ------------- 1,400 miles
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------------------ oxygen/magnesium --- 0.5 Solar Mass ------------- 5,200 miles
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------------------ carbon/oxygen --------- 6.2 Solar Mass ------------- 47,000 miles
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------------------ helium ------------------ 2.2 Solar Mass ------------- 560,000 miles
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------------------ hydrogen -------------- 10.6 Solar Mass ------------- blown away
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- It is only the heat and radiation emitted from the fusion that fights the collapse created by gravity. When the fusion ends gravity wins. The star collapses into the core and there is a giant rebound, an explosion that blows most all of the mass of the star into space.
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- If the remaining core after the explosion is greater than 3.5 Solar Mass the gravity will continue into a Blackhole. If the remnant core is less it will collapse into a Neutron Star. If the star was rotating the conservation of angular momentum will spin up the collapsed core into a rapid rotation. The centripetal force of the in falling spinning material creates a spinning accretion disk.
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- The poles of the rotating star become 1,000 times less dense that the equator. Powerful magnetic fields are generated by the rotating ionized particles. The magnetic field accelerates the charged particles along the path of least resistance which is out the poles of rotation. Material blasts out of the star’s spin axis at 99.5% the speed of light. This whole process took only 7 seconds. I hope you were paying attention.
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- When the accelerated material jets smash into gases surrounding the star Gamma Rays are generated. The rotating magnetic field continues to contain the jets to within 5 arc degrees. The jets continue to interact with gases further out from the star emitting other energies of the electromagnetic spectrum, X-rays, light, radio waves.
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- This lower energy radiation is the after glow Visible light is 2 to 3 electron volts. A dental X-ray is 60,000 electron volts for comparison.
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May 18, 2022 GAMMA RAYS - where do they come from? 1158 1160 3581
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