Term
| History of Gamma Ray Bursts |
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Definition
-discovered accidently in 1967 by Vela Satellites
-the mystery: we see bursts of energy in gamma rays from outter space once or twice a day, lasting only a few seconds
-the energy coming every few seconds is more than our sun produces in its entire lifetime
-Launched in 1991, the Compton Gamma-ray Observatory made the first important discovery about GRB when it established that the explosions are coming from random directions (and therefore large distances)
-In 1997 the BeppoSax satallite made the next important discovery when it localized long-bursts to 5 arcmins. This led to the discovery of afterglow radiation and distance measurements. |
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Term
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Definition
-Long GRB's are exclusively in star-forming galaxies
-Seen once or twice a day and they last for a few seconds
-Explosions causing GRB occur when certain types of stars die or when neutron stars collide, they usually herald the birth of a black hole |
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Term
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Definition
Gas & Dust Cloud --> main sequence stars (10 million years) --> mass loss turns it into a Supergiant --> turns into one of the following:
1) Type II supernova --> Neutron Star and supernova remanent
2) Black hole & accretion disc |
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Term
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Definition
-produced when Gamma Ray Bursts jet shocks and heats the medium in the vicinity of the explosion, and accelerates electrons which radiate via synchrotron process
-the long lasting radiation following the brief GRB |
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Term
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Definition
-last less than 1 minute
-explosions causing GRB last for days to months |
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Term
| Faster-than-light apparent speed of a GRB |
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Definition
| implies an apparent speed near the speed of light |
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Term
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Definition
-launched November 20, 2004
-made important discoveries regarding GRB
-observed bursts that occurred when the universe was less than a billion years old, these are some of the most distant objects we have ever seen |
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Term
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Definition
-rotating neutron stars that have strong magnetic fields
-the combo of its fast rotation and strong magnetic field causes powerful radiation
-typical pulsar rotates once per second
-has a magnetic field 1 trillion times that of the earth
-an object of about 1 solar masses that spins a few times per second MUST be small like a neutron star or it would be shattered
-Hewish and Bell discover radio pulsars in 1967
-Hewish won Nobel peace price in 1974
-period increases with time, and thus rotational kinetic energy decreases with time
-when the period becomes greater than 1 second, it stops pulsating
-the magnetic field is determined from the rate of change of its period |
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Term
| Facts about neutron stars |
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Definition
-max mass of neutron star ~ 2 solar masses
-Roughly 100 million to a billion neutron stars in our galaxy alone, we can only see about 2000 of them though
- 1 cubic cm of a neutron star weighs 4 times that of the combined weight of all the people in the world
-No nuclear fuel left to burn |
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Term
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Definition
| rotating, magnetic neutron stars with magnetic axis tilted with respect to its spin axis |
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Term
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Definition
-a type of neutron that taps into the magnetic field reservoir and sometimes produces spectacular outbursts
-they have a much stronger magnetic field than that of an average pulsar (~10^15 Gauss, instead of ~10^12 Gauss)
-occasionally Magnetars release their energy in a spectacular explosions called "soft Gamma Ray Repeaters", which are thought to be similar to gigantic solar flares |
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Term
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Definition
-explosions of magnetic energy from Magnetars
-There are four known soft gamma ray repeaters |
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Term
| The amazing outburst of December 27, 2004 |
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Definition
- "The day the earth survived the greatest stellar attack ever"
-Came suddenly from beyond the Sagittarius constellation, some 50,000 lightyears away
-In a couple of seconds, A magnetar produced an invisible burst of energy equivalent to half a million years of sunlight |
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Term
| Neutron Stars in binary systems |
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Definition
-most known radio and gamma-ray pulsars are found alone, however some 2 dozen neutron stars are found in binary systems
-they accrete mass through an accretion disc and produce X-rays
-Uhuru satellite launched from Kenya in 1972 found that the sky was ablaze with X-rays. These sources turned out to be neutron stars in a binary system with black holes
-The Chandra Observatory and the Fermi Observatory have also observed these binary systems
-matter from the accretion disc flows along the magnetic field lines, and thus falls onto the neutron star at its poles, emitting X-rays as a result
-Its rotation combined with a tilted magnetic field (with respect to its rotation axis) give off X-ray "pulses" by the lighthouse effect
-20% of the mass dropped onto the neutron star is converted to energy (nuclear reactions only convert 1% of the mass into energy, so this is highly efficient) |
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Term
| Anomolous X-ray Pulsars (AXP's) |
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Definition
-5 confirmed cases
-No radio emission
-None in binary systems
-2 or 3 related to supernova remnants
-The most likely energy source of a AXP is the dissipation of it's magnetic field |
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Term
| The correct theory of Gravity |
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Definition
-Einstein's Theory of General Relativity
-Newton's theory holds when gravity is weak, but not when it is strong |
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Term
| The correct theory of Gravity |
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Definition
| Einstein's Theory of General Relativity |
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Term
| Bubbles of Energy at the center of the Galaxy |
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Definition
-This bubble is gamma-ray radiation, first detected by Fermi Satellite
-most likely caused by a black hole at the center of our galaxy |
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Term
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Definition
-Objects with gravity so strong that nothing, not even light, can escape it
-Observed at the center of most galaxies
-The event horizon is the boundary between where light can escape and where it cannot. The radius of the event horizon is called the Schwarzschild Radius |
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Term
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Definition
| the boundary in a black hole between where light can escape and where light cannot escape |
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Definition
| the radius of the event horizon |
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Term
| Fundamental Properties of a black hole |
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Definition
-electrical charge (usually taken to be zero)
-spin (or angular momentum)
-mass
-all other information is "lost" when an object falls into a black hole (the composition of the object is irrelevant) |
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Term
| The spectrum of radiation from black holes |
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Definition
| the spectrum of radiation from black holes is that of a black-body at a temperature inversely proportional to the mass of the black hole |
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Term
| Fundamental Properties of a black hole |
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Definition
-electrical charge (usually taken to be zero)
-spin (or angular momentum)
-mass
-all other information is "lost" when an object falls into a black hole (the composition of the object is irrelevant) |
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Term
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Definition
-the radiation from black holes
-the spectrum of radiation from black holes is that of a black-body at a temperature inversely proportional to the mass of the black hole |
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Term
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Definition
1. Regular, with a mass of a few solar masses. Massive stars turn into regular black holes after they die in supernova explosions
2. Supermassive black holes. We understand what the do but not where the come from |
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Term
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Definition
| Look for accretion in a binary system and at the center of galaxies! |
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