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Post Info TOPIC: The Crab Nebula


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RE: The Crab Nebula

According to the folklore of the Celts and other ancient cultures, Halloween marked the midpoint between the autumnal equinox and the winter solstice on the astronomical calendar, a spooky night when spirits of the dead spread havoc upon their return to Earth.
Nowadays, Halloween is primarily a time for children to dress in costume and demand treats, but the original spirit of Halloween lives on in the sky in the guise of the Crab Nebula.
A star's spectacular death in the constellation Taurus was observed on Earth as the supernova of 1054 A.D. Now, almost a thousand years later, a superdense neutron star left behind by the stellar death is spewing out a blizzard of extremely high-energy particles into the expanding debris field known as the Crab Nebula.

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This composite image uses data from three of NASA's Great Observatories. The Chandra X-ray image is shown in light blue, the Hubble Space Telescope optical images are in green and dark blue, and the Spitzer Space Telescope's infrared image is in red. The size of the X-ray image is smaller than the others because ultrahigh-energy X-ray emitting electrons radiate away their energy more quickly than the lower-energy electrons emitting optical and infrared light. The neutron star, which has the mass equivalent to the sun crammed into a rapidly spinning ball of neutrons twelve miles across, is the bright white dot in the centre of the image.




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Title: Observations of the Crab Nebula with H.E.S.S
Authors: The HESS Collaboration: F.Aharonian, et al

The Crab nebula was observed with the H.E.S.S. stereoscopic Cherenkov-telescope array between October 2003 and January 2005 for a total of 22.9 hours (after data quality selection). Observations were made with three operational telescopes in late 2003 and with the complete 4 telescope array in January - February 2004 and October 2004 - January 2005.
The observations are discussed and used as an example to detail the flux and spectral analysis procedures of H.E.S.S., and to evaluate the systematic uncertainties in H.E.S.S. flux measurements. The flux and spectrum of gamma-rays from the source are calculated on run-by-run and monthly time-scales, and a correction is applied for long-term variations in the detector sensitivity. Comparisons of the measured flux and spectrum over the observation period, along with the results from a number of different analysis procedures are used to estimate systematic uncertainties in the measurements.
The energy spectrum is found to follow a power law with an exponential cutoff, with photon index $\Gamma = 2.39 ±0.03stat and cutoff energy E_c = (14.3 ±2.1stat TeV between 440 GeV and 40 TeV. The observed integral flux above 1 TeV is $(2.26 ± 0.08stat X 10^-11 cm^-2 s^-1. The estimated systematic error on the flux measurement is estimated to be 20%, while the estimated systematic error on the spectral slope is 0.1.

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A new Hubble image - among the largest ever produced with the Earth-orbiting observatory - gives the most detailed view so far of the entire Crab Nebula. The Crab is arguably the single most interesting object, as well as one of the most studied, in all of astronomy. The image is the largest ever taken with Hubble’s WFPC2 workhorse camera.

Expand (176kb, 1024 x 768)
Supernova Remnant
Position (2000): R.A. 05h 34m 32s Dec. 22° 00' 52"
The image is 6 arcminutes along the bottom (12 light-years).

The Crab Nebula, in the constellation Taurus, is one of the most intricately structured and highly dynamical objects ever observed. The new Hubble image of the Crab was assembled from 24 individual exposures taken with the NASA/ESA Hubble Space Telescope’s Wide Field and Planetary Camera 2 (WPFC2) and is the highest resolution image of the entire Crab Nebula ever made.

The Crab Nebula is a six-light-year-wide expanding remnant of a star’s supernova explosion. Japanese and Chinese astronomers witnessed this violent event nearly 1,000 years ago in 1054.

The filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the centre of the nebula, only barely visible in this Hubble image, is the dynamo powering the nebula’s eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star's rotation. A neutron star is the crushed ultra-dense core of the exploded star.

The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as large ground-based telescopes such as ESO’s Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.

The newly composed image was assembled from individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000. The colours in the image indicate the different elements that were expelled during the explosion. Blue indicates neutral oxygen, green singly ionised sulphur and red doubly-ionised ionised oxygen. The Hubble data have been superimposed onto images taken with the European Southern Observatory’s Very Large Telescope at Paranal Observatory, Chile.



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The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion.

IMAGE (800 X 600)

The image, taken by the Nordic Optical Telescope (NOT), is in false colours. The Crab Nebula spans about 10 light-years. In the nebula's very centre lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town.
The Crab Pulsar rotates about 30 times each second.

Credit & Copyright: Walter Nowotny (U. Wien, Nordic Optical Telescope



Posts: 131433

If you've ever wondered where the iron in your blood comes from, it was forged in the heart of a massive star. But the gold and silver in your jewellery, plus mercury, lead and other heavy metals we find useful, were created when that star exploded in a supernova. When a supernova explodes, it ejects huge amounts of gas and dust into interstellar space, where they become the building blocks of stellar systems like our solar system. Remnants of recent supernova explosions therefore have much to tell about the origins of our world.

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Position(2000): RA 05 : 34.5 Dec +22 : 01

A University of Minnesota team of astronomers has studied the Crab Nebula, a filamentous remnant of a star that exploded in A.D. 1054 in the constellation Taurus.
Using the new Spitzer Space Telescope, which operates at infrared wavelengths, the team found that a crucial type of dust has gone missing. The astronomers will present their findings at 10 a.m. Wednesday, June 1, at the American Astronomical Society meeting in the Minneapolis Convention Centre.

The team leader was graduate student Tea Temim. Her advisers, astronomy professors Robert Gehrz and Charles Woodward, are among the co-authors of the paper. They are all infrared astronomers interested in how cosmic dust forms and recondenses into a new generation of stars with planets.
Our sun is at least a second-generation star, built from the dusty, gaseous wreckage of previous stars.
Cosmic dust is composed of any fine solid particles in space except ices. It is much finer than beach sand; it's more like smoke particles. It forms from the aggregation of gas molecules and very fine particles into even bigger particles--like the nucleation of water to make raindrops. Since very fine dust has been observed to form in the ejected material of another supernova only a few years after it exploded (Supernova 1987A, detected in 1987), the scientists expected to find plenty of it in a relatively young supernova remnant like the Crab Nebula.
Instead, the Spitzer data showed only much coarser dust--particles that, although only a few millionths of a meter in size, were still 10 to 100 times larger than the fine stuff.
The big question is, what could have destroyed or spirited away the smallest dust particles?
One possible culprit is the rapidly spinning neutron star at the core of the Crab Nebula. It is pumping out intense ultraviolet radiation, which might be evaporating small particles. The core is also throwing out protons and electrons at speeds approaching the speed of light, and these could also be destroying the fine dust. One reason this is an attractive explanation is that fine dust forms within a year of an explosion, but the intense radiation from the core doesn't develop until long after coarse dust has coalesced.

Temim has mapped the energy distribution from these ultra fast particles (called synchrotron radiation) coming from the neutron star. This will show how these particles spread out and mix with the rest of the ejected material.
The Crab Nebula( also know as M1) is 6,500 light-years away--that's 30,000 times the distance of Earth from the sun, in the constellation Taurus. The nebula is five light-years across, which is bigger than the distance between the sun and its nearest star.
The Crab Nebula has been photographed in the X-ray, radio and visible parts of the spectrum.

"The images are exciting because we're filling in the puzzle with infrared. Infrared is where we can find out information about the formation of dust" - Tea Temim.
These images could not have been made from a ground-based telescope because Earth's atmosphere filters out much infrared light. Spitzer can pick up faint infrared signals only because it is cooled to minus 450 degrees F; if it were much warmer, its own heat would drown out the signals from the Crab.

A note on how dust forms in a supernova. A massive star, during the course of its life, derives its energy from synthesizing elements as heavy as iron (of the 92 naturally occurring elements, iron is the 26th heaviest). When the star uses up its fuel, its core collapses, forcing protons and electrons together, forming neutrons. But, as Isaac Newton said, every action has an equal and opposite reaction.
After collapsing, the star explodes, shooting neutrons and small atomic nuclei into each other to form new nuclei. Some of these nuclei are bigger than iron. Ordinarily, they would undergo radioactive decay, but as they are shot away from their parent star by the explosion they cool before decay can occur.
All these elements coalesce to form dust. The iron in our blood comes from the iron forged in these big stars, and the gold, silver, mercury, lead and other heavy elements we find so useful are forged in the supernova explosion.


This spectacular supernova explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers. According to the records, it was visible in daylight for 23 days, and was about four times brighter than Venus( about mag -6) , and 653 days to the naked eye in the night sky.
The filaments are mysterious because they appear to have less mass than expelled in the original supernova and higher speed than expected from a free explosion. In the above picture taken recently from a Very Large Telescope, the colour indicates what is happening to the electrons in different parts of the Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen, while blue indicates the electrons are whirling around the magnetic field of the inner nebula. In the nebula's very centre lies a pulsar: a neutron star rotating, in this case, 30 times a second.
In the visible light, the pulsar is of 16th apparent magnitude. This means that this very small star is roughly of absolute magnitude +4.5, or about the same luminosity as our sun in the visible part of the spectrum !

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