- 2821 - GAMMA RAY BURSTS - how often it happens? Would you like to see the most powerful explosion that occurs in the Universe? Don’t worry you do not have to stand too close. These explosions are at least 2,000,000,000 lightyears away. They occur once a day on average and one of these occurred in the constellation Hydra. Log on to http://grb.sonoma.edu/ and see the sky map with the Gamma Ray Bursts exploding in real time.
--------------- 2821 - GAMMA RAY BURSTS - how often it happens?
- For example: GRB061021 happened at 10:15 on October 27, 2006. The Burst was detected by the satellite SWIFT and its location was given in Right Ascension and Declination so every one interested could find it and study it. Highlight the Burst entry in the table and see a brief description of the event. Click on more information and see the light curve that was detected by the satellite.
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- In the table the satellites are identified as Missions. “Integral” was launched in October, 2002 and is the most sensitive Gamma-Ray observatory ever launched. Unfortunately, it is slow in moving its instruments in place to study a Burst that is detected. Bursts only last 2 to 20 seconds.
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- SWIFT was launched in November, 2004. It was designed to look at a broad patch of sky and then move its precision instruments quickly in order to study the Burst before it fades away. SWIFT has three telescopes on board. The Burst Alert Gamma-Ray Telescope views 1/6 of the sky at one time. As soon as a Burst is detected it swings its X-ray telescope and its optical/ultraviolet telescope in for a precision measurement.
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- If you could see Gamma-Ray Bursts they would be very annoying. They go off once a day and they would be the brightest thing in the sky. They have the shining power of 100,000,000,000,000 Suns. Fortunately they are 2,000,000,000 light years away so they are much dimmer than that but they are still easy to detect with the right telescope.. Just not with your eyes because most of the radiation is in Gamma-rays or X-rays that your eyes can not see.
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- The Sun puts our 3.90 * 10^26 watts of energy, or Joules of energy per second. Surprisingly the energy in Gamma-Ray Bursts is fairly constant and calculated to be 10^51 ergs. One Erg is 10^-7 Joules, so the Burst is 10^44 Joules.
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- So, with the Sun’s energy output it would take 2.6^10^17 seconds to produce that much energy. Or, the Gamma-Ray Bursts puts out as much energy in 20 seconds as the Sun does in 80,000,000 years. That is the reason we call it the most powerful explosion in the Universe.
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- As of August, 2006 SWIFT had detected 140 Bursts. About half of these were spotted soon enough to observe the afterglows from the burst allowing astronomers to determine the Burst’s location. After much study astronomers now know what causes Gamma-Ray Bursts and how they produce this enormous energy:
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- The are two types of Bursts, short duration, under 2 seconds and long duration averaging 20 seconds. The 20 second Bursts are the result of a supernova explosion.
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- Stars with greater than 30 Solar Mass that are at the end of their lives because they have burned up all their nuclear fuel. These stars live only 1 to 10 million years. Their enormous gravity causes nuclear fusion to burn through hydrogen quickly into helium, then carbon, then oxygen, then silicon then iron. These elements form in layers in the star like an onion.
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- At the center remains iron and fusion does not work with iron. The nuclear engine therefore stops with the fusion of iron. In less than a second when this happens the star collapses due to the force of gravity. The gravity is so intense the center becomes dense enough to become a Black Hole.
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- The spinning Black Hole has a spinning accretion disk forming around it at the center of the star. The spinning accretion disk is a dynamo of charged particles that create an enormous magnetic field. High speed jets from the disk shoot the charged particles out the dynamos rotational poles.
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- The jets quickly tunnel through the layers to the surface and exit at speeds near the speed of light. The jets and the solar wind from the accretion disk blow the star apart in a giant supernova explosion.
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- The jets continue to speed away along the poles at relativistic speeds smashing particles together. These collisions produce the Gamma-Ray Burst radiation. As the jets exit further they loose energy and the collisions with interstellar matter produce lower energy radiation in the form of X-rays, optical and radio afterglows.
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- How can a Black Hole that consumes everything, even light, shoot out material in a supernova explosion?
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- The answer is that it is the power of the magnetic field and the accretion disk that is outside the Black Hole’s event horizon that causes all this to happen. The Black Hole remains at the center of the star and all the explosion that takes place is outside its event horizon.
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- The jets themselves are narrow, 1 to 5 degrees. Only if the jets are aimed within 5 degrees of Earth can astronomers detect the highest energy particles, the Gamma-Rays.
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- The Gamma-Rays last only as long as it takes the Black Hole to consume the inner core, usually 20 seconds. This narrow beam means that if we see one Burst per day there must be 500 to 1000 per day that we do not see because the jets are pointing in another direction.
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- Astronomers believe that there are 1,500 Bursts occurring every day, which calculates out to a Black Hole being formed in a supernova every minute of the day.
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- The short duration bursts lasting from milliseconds up to 2 seconds originate in the merger of 2 neutron stars or a neutron star and a Black Hole. And, these Bursts lie between 2 and 3 billion lightyears away.
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- Go to http://www.phys-astro.sonoma.edu/ and you can learn a lot more about SWIFT and the discovery of Gamma-Ray Bursts.
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- September 8, 2020 711 2821
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