* Astronomy

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RE: The Crab Nebula

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Crab Pulsar Dazzles Astronomers with its Gamma-Ray Beams

A thousand years ago, a brilliant beacon of light blazed in the sky, shining brightly enough to be seen even in daytime for almost a month. Native American and Chinese observers recorded the eye-catching event. We now know that they witnessed an exploding star, which left behind a gaseous remnant known as the Crab Nebula.
The same object that dazzled skygazers in 1054 C.E. continues to dazzle astronomers today by pumping out radiation at higher energies than anyone expected. Researchers have detected pulses of gamma rays with energies exceeding 100 billion electron-volts (100 GeV) -- a million times more energetic than medical X-rays and 100 billion times more than visible light.
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SN1054, the supernova of 1054, is a supernova that was observed as a new "star" in the sky beginning in July, 1054 AD, and lasted for a period of approximately two years. Many documents from the Chinese world record the event, which was also noted in a document from the Arab world.
The sky on the morning of 4 July, probable date of the first Chinese observation of the supernova.
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The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The nebula was observed by John Bevis in 1731; it corresponds to a bright supernova recorded by Chinese and Arab astronomers in 1054.
Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between apparent magnitude -7 and -4.5 (brighter than everything in the night sky except the Moon) by July. The supernova was visible to the naked eye for about two years after its first observation.
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On July 4, 1054 A.D., Chinese astronomers noted a "guest star" in the constellation Taurus; Simon Mitton lists 5 independent preserved Far-East records of this event (one of 75 authentic guest stars - novae and supernovae, excluding comets - systematically recorded by Chinese astronomers between 532 B.C. and 1064 A.D., according to Simon Mitton). This star became about 4 times brighter than Venus in its brightest light, or about mag -6, and was visible in daylight for 23 days.
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A new movie from NASA's Chandra X-ray Observatory shows a sequence of Chandra images of the Crab Nebula, taken over an interval of seven months. Dramatic variations are seen, including the expansion of a ring of X-ray emission around the pulsar (white dot near center) and changes in the knots within this ring.
However, arguably the most striking result of these observations is the variations that were not observed, or in analogy with a famous Sherlock Holmes story, this could be a case where the fact that the dog that did not bark helps to solve a mystery.

Credit: NASA/CXC/MSFC/M.Weisskopf et al

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Crab Nebula's gamma-ray flare mystifies astronomers

The Crab Nebula has shocked astronomers by emitting an unprecedented blast of gamma rays, the highest-energy light in the Universe.
The cause of the 12 April gamma-ray flare, described at the Third Fermi Symposium in Rome, is a total mystery.
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Physicists Discover Crab Nebula is Slowly Dimming

The Crab Nebula, once considered to be a source of energy so stable that astronomers used it to calibrate their instruments, is dimming. LSU physicists Mike Cherry, Gary Case and graduate student James Rodi, together with an international team of colleagues using the Gamma-ray Burst Monitor, or GBM, on NASA's Fermi gamma-ray space telescope, discovered the anomaly. This revelation has proven astonishing for astronomers.
The Crab Nebula, one of the most studied objects in the sky, is the wreckage of a star that exploded in 1054. Considered a cornerstone of astronomical research, it even inspired its own unit of measurement, the "millicrab," which is used as a standard for measuring the intensity from other high-energy sources.
The GBM instrument was launched into orbit in summer 2008. This summer, the scientists were working on a catalogue of the high energy X-ray and gamma ray signals detected mainly from sources in the galaxy powered by black holes and neutron stars. As they were preparing the catalog, which has been accepted for publication in the Astrophysical Journal, they realised that the intensity coming from the Crab Nebula was dimming.
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Fermi's Large Area Telescope Sees Surprising Flares in Crab Nebula

The Crab Nebula, one of our best-known and most stable neighbours in the winter sky, is shocking scientists with its propensity for fireworks - gamma-ray flares set off by the most energetic particles ever traced to a specific astronomical object. The discovery, reported today by scientists working with two orbiting telescopes, is leading researchers to rethink their ideas of how cosmic particles are accelerated.
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Mystery flares betray hidden force within Crab nebula

Forget the Large Hadron Collider: an interstellar dust cloud called the Crab nebula has been identified as the most powerful known particle accelerator in the universe. But exactly how it boosts particles to record-breaking speeds is a mystery. The finding also adds an extra complication for astronomers who use the Crab to calibrate their instruments.

Two orbiting telescopes have revealed that the nebula, which sits some 6500 light years from Earth, releases brief, bright flares of gamma-rays, a pair of papers released today report. These flares are most likely produced by electrons that have been whipped up to record-breaking speeds.