GAMMA RAY ERUPTION IN THE CRAB NEBULA May 11, 2011Posted by jcconwell in Astronomy, Neutron Stars.
Tags: Crab Nebula, Gamma Ray Eruption, neutron star
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WASHINGTON (NASA) — The famous Crab Nebula supernova remnant has erupted in an enormous flare five times more powerful than any flare previously seen from the object. On April 12, NASA’s Fermi Gamma-ray Space Telescope first detected the outburst, which lasted six days.
The nebula is the wreckage of an exploded star that emitted light which reached Earth in the year 1054. It is located 6,500 light-years away in the constellation Taurus. At the heart of an expanding gas cloud lies what is left of the original star’s core, a superdense neutron star that spins 30 times a second. With each rotation, the star swings intense beams of radiation toward Earth, creating the pulsed emission characteristic of spinning neutron stars (also known as pulsars).
Apart from these pulses, astrophysicists believed the Crab Nebula was a virtually constant source of high-energy radiation. But in January, scientists associated with several orbiting observatories, including NASA’s Fermi, Swift and Rossi X-ray Timing Explorer, reported long-term brightness changes at X-ray energies.
Since 2009, Fermi and the Italian Space Agency’s AGILE satellite have detected several short-lived gamma-ray flares at energies greater than 100 million electron volts (eV) — hundreds of times higher than the nebula’s observed X-ray variations. For comparison, visible light has energies between 2 and 3 eV.
On April 12, Fermi’s LAT, and later AGILE, detected a flare that grew about 30 times more energetic than the nebula’s normal gamma-ray output and about five times more powerful than previous outbursts. On April 16, an even brighter flare erupted, but within a couple of days, the unusual activity completely faded out.
“These superflares are the most intense outbursts we’ve seen to date, and they are all extremely puzzling events,” said Alice Harding at NASA’s Goddard Space Flight Center in Greenbelt, Md. “We think they are caused by sudden rearrangements of the magnetic field not far from the neutron star, but exactly where that’s happening remains a mystery.”
Extreme Universe: The Most Massive Neutron Star October 27, 2010Posted by jcconwell in Astronomy, Extreme Universe, General Relativity, Neutron Stars.
Tags: most massive neutron star, neutron star, PSR J1614-2230
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Using the National Science Foundation’s Green Bank Telescope , astronomers have discovered the most massive neutron star ever, this discovery will offer profound insight on the limits of neutron stars and the nature of matter under such extreme conditions.
“This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out,” said Paul Demorest, of the National Radio Astronomy Observatory (NRAO). “This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics,” he added.
The neutron star, called PSR J1614-2230 contains twice the mass of the Sun but compressed down into pulsar that is smaller than 20 kilometer It is estimated cubic inch of material from the star could weigh more than 10 billion tons. I have two videos below with more details for you.
The first is about the Discovery
The second is about the Instruments
New EINSTEIN@HOME effort launched March 25, 2009Posted by jcconwell in Astronomy, Neutron Stars.
Tags: Astronomy, neutron star
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Einstein@Home, based at the University of Wisconsin–Milwaukee (UWM) and the Albert Einstein Institute (AEI) in Germany, is one of the world’s largest public volunteer distributed computing projects. More than 200,000 people have signed up for the project and donated time on their computers to search gravitational wave data for signals from unknown pulsars.
Today, Prof. Bruce Allen, Director of the Einstein@Home project, and Prof. Jim Cordes, of Cornell University and Chair of the Arecibo PALFA Consortium, announced that the Einstein@Home project is beginning to analyze data taken by the PALFA Consortium at the Arecibo Observatory in Puerto Rico. The Arecibo Observatory is the largest single-aperture radio telescope on the planet and is used for studies of pulsars, galaxies, and the Earth’s atmosphere. Using new methods developed at the AEI, Einstein@Home will search Arecibo radio data to find binary systems consisting of the most extreme objects in the universe: a spinning neutron star orbiting another neutron star or a black hole. Current searches of radio data lose sensitivity for orbital periods shorter than about 50 minutes. But the enormous computational capabilities of the Einstein@Home project (equivalent to tens of thousands of computers) make it possible to detect pulsars in binary systems with orbital periods as short as 11 minutes.
“Discovery of a pulsar orbiting a neutron star or black hole, with a sub-hour orbital period, would provide tremendous opportunities to test General Relativity and to estimate how often such binaries merge,” said Cordes. The mergers of such systems are among the rarest and most spectacular events in the universe. They emit bursts of gravitational waves that current detectors might be able to detect, and they are also thought to emit bursts of gamma rays just before the merged stars collapse to form a black hole. Cordes added: “The Einstein@Home computing resources are a perfect complement to the data management systems at the Cornell Center for Advanced Computing and the other PALFA institutions.”
Extreme Universe: Magnetic Fields and Magnetars March 12, 2009Posted by jcconwell in Astronomy, Extreme Universe, Gamma Ray Bursts, Neutron Stars.
Tags: Astronomy, Gamma Ray Burst, magnetar, neutron star
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Neutron Stars are extreme to begin with, but magnetars add a whole new level of extreme to these exotic objects. Magnetars, as the name implies, are neutron stars with ultra high magnetic fields. As a matter of fact, the most extreme magnetic fields ever found in the universe!
There are about 15 magnetars known, they are all examples of a class of objects called “soft gamma repeaters” . The most magnetic one, and the most magnetized object in the known universe is SGR 1806-20. The magnetic field of this magnetar is estimated to be about 2 x 1011 Teslas or 2 x 1015 gauss, one Tesla being equal to 10,000 gauss.
Now, to give you some sense of how big this is, the Earth’s magnetic field is about 1/2 gauss or .00005 Tesla. The magnet in a hospital’s MRI is about 3.2 Tesla or 32,000 gauss, and the largest sustained magnetic field created in a lab is about 40 Tesla.
So we’re talking about magnetic fields 1000 trillion times bigger than the Earth’s field. Very weird things can happen with fields this large. One thing that’s interesting is how much energy is stored in such a field. So let’s break out an equation from physics and use an example I did in my electricity & magnetism class last week. If you look it up, you’ll find the energy per cubic meter, or energy density, of a magnetic field is given by:
u = B2/2 μ0
u is the energy density given in Joules per cubic meter. A Joule is the energy you use to lift a kilogram about 10 centimeters off the ground.
B is the strength of the magnetic field given in Teslas, and μo is a constant that has a value of 4π x 10-7 (it has units , but we’ll ignore them). Using a field of B = 2 x 1011 Teslas, the most powerful magnetar, we will get a huge number…
1.6 x 1028 Joules/(cubic meter)
or every cubic meter contains this amount of energy. To put this in context, the largest hydrogen bombs have a yield of 20 Megatons of TNT, which is about 1017 Joules of energy. So in each cubic meter of magnetic field has the stored energy of 160,000,000,000 (160 billion), 20 Megaton bombs.
Since we’re having so much fun, lets think about it this way. Einstein showed mass and energy are equivalent, so how much mass would one cubic meter of this HUGE magnetic field have? Well…
or m = E/ c2 = 1.6 x 1028 Joules/(3 x 108m/s)2 = 1.78 x 1011kilograms
Each cubic centimeter of magnetic field would have a mass of 178 metric tons!!! If you multiply this by the number of cubic meters in the Magnetar, about 40 trillion, assuming the whole neutron star is magnetized, you get a lot of magnetic energy stored in Magnetar.
To give you an idea of what a small amount of this energy would do, consider the events of December 27, 2004. On that day the magnetar we’ve been using as a example, SGR 1806-20, under went a “superflare”. The “superflare,” from a magnetar named SGR 1806–20, irradiated Earth with more total energy than a powerful solar flare. Yet this object is an estimated 50,000 light-years away in Sagittarius. During that flicker of time it outshone the full Moon by a factor of two. The gamma rays struck the ionosphere and created more ionization which briefly expanded the ionosphere. Assuming that the distance estimate is accurate, the magnetar must have let loose as much energy as the Sun generates in 250,000 years.