Crab Nebula - M1

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apod.nasa.gov/apod/supernova_remnants.html

The Crab Nebula is cataloged as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunning time-lapse movie. In each year from 2008 to 2017, an image was produced with the same telescope and camera from a remote observatory in Austria. Combined in the time-lapse movie, the 10 images represent 32 hours of total integration time. The sharp, processed frames even reveal the dynamic energetic emission within the incredible expanding Crab. The Crab Nebula lies about 6,500 light-years away in the constellation Taurus.



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What causes the blue light in the Crab Nebula?

Electrons whirling at nearly the speed of light around the star’s magnetic field lines produce the eerie blue light in the interior of the nebula. The neutron star, like a lighthouse, ejects twin beams of radiation that make it appear to pulse 30 times per second as it rotates.

What are the filaments of the Crab Nebula?

The blue in the filaments in the outer part of the nebula represents neutral oxygen. Green is singly ionized sulfur, and red indicates doubly ionized oxygen. These elements were expelled during the supernova explosion. A rapidly spinning neutron star (the ultra-dense core of the exploded star) is embedded in the center of the Crab Nebula.

The filaments of Crab Nebula are made up from carbon, oxygen, nitrogen, iron, neon, sulfur and ionized helium and hydrogen. They are the remnants of its progenitor star’s atmosphere where the typical temperature is between 11,000 and 18,000K (Kelvin). On average it’s 15,000 Celsius and their densities are about 1,300 particles per cm3.

M1- Movie of the Crab Nebula!

www.astrobin.com/full/327338/0/

In the nebula's very center 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.

Perhaps we should be seeing M1 like this:

en.wikipedia.org/wiki/Crab_Nebula:

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The common name comes from William Parsons, 3rd Earl of Rosse, who observed the object in 1842 using a 36-inch (91 cm) telescope and produced a drawing that looked somewhat like a crab. The nebula was discovered by English astronomer John Bevis in 1731, and it corresponds with a bright supernova recorded by Chinese astronomers in 1054. The nebula was the first astronomical object identified that corresponds with a historical supernova explosion.

At an apparent magnitude of 8.4, comparable to that of Saturn's moon Titan, it is not visible to the naked eye but can be made out using binoculars under favourable conditions. The nebula lies in the Perseus Arm of the Milky Way galaxy, at a distance of about 2.0 kiloparsecs (6,500 ly) from Earth. It has a diameter of 3.4 parsecs (11 ly), corresponding to an apparent diameter of some 7 arcminutes, and is expanding at a rate of about 1,500 kilometres per second (930 mi/s), or 0.5% of the speed of light.

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 kilometres (17–19 mi) across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. At X-ray and gamma ray energies above 30 keV, the Crab Nebula is generally the brightest persistent gamma-ray source in the sky, with measured flux extending to above 10 TeV. The nebula's radiation allows detailed study of celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab Nebula's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.

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articles.adsabs.harvard.edu/pdf/1987ApJ...322..206N

1987ApJ. . .322. .206N
The Astrophysical Journal, 322:206-214,1987 November 1 © 1987. The American Astronomical Society. All rights reserved. Printed in U.S.A.
EVOLUTION OF 8-10 M0 STARS TOWARD ELECTRON CAPTURE SUPERNOVAE. II.
COLLAPSE OF AN O + Ne + Mg CORE1
Ken’ichi Nomoto
Department of Physics, Brookhaven National Laboratory; and Department of Earth Science and Astronomy, University of Tokyo Received 1987 January 13; accepted 1987 April 6

ABSTRACT
A helium core of an 8.8 M0 star (initial core mass of 2.2 MG) is evolved from the helium-burning stage
through the early stage of collapse of an O + Ne 4- Mg core. The evolution is similar to the 9.6 M0 star
studied earlier; i.e., after nondegenerate carbon burning, the star forms a strongly degenerate O + Ne + Mg
core because its mass, 1.28 M0, is smaller than the critical mass for neon ignition. The penetration of the
surface convection zone into the helium layer takes place earlier than in the 9.6 M0 star, i.e., during carbon-
burning phase. After most of the helium layer is dredged up, the degenerate core grows through the hydrogen-
helium double-shell burning. When the mass interior to helium-burning shell (i.e., O + Ne + Mg core plus
C + O layer) reaches 1.38 M0, electron captures 24Mgfe v)24Na(e, v)24Ne, and 20Ne(e, v)20F(é?, v)20O start
and induce the rapid contraction of the core. Entropy production associated with electron capture on 20Ne as
well as gravitational contraction leads to an ignition of the oxygen deflagration that incinerates the core
material into nuclear statistical equilibrium (NSE). Electron capture in the NSE layer accelerates the collapse.
Calculation is carried out through the neutrino trapping density. The star will become a Type II supernova to
leave a neutron star less massive than 1.3 MG. The effects of oxygen burning upon the hydrodynamic behav-
ior of collapse and the possible nucleosynthetic yields are discussed.
Subject headings: nebulae: Crab Nebula — nucleosynthesis — stars: evolution — stars: interiors —
stars: supernovae

M1 Crab Nebula

iopscience.iop.org/article/10.1088/0004-6256/144/1/27/pdf

ELEMENT DISTRIBUTIONS IN THE CRAB NEBULA∗
Timothy J. Satterfield1, Andrea M. Katz1, Adam R. Sibley1, Gordon M. MacAlpine1, and Alan Uomoto2
1 Department of Physics and Astronomy, Trinity University, San Antonio, TX 78212, USA
2 Carnegie Institution for Science, The Observatories, Pasadena, CA 91101, USA
Received 2011 November 22; accepted 2012 May 17; published 2012 June 14

ABSTRACT
Images of the Crab Nebula have been obtained through custom interference filters that transmit emission from
the expanding supernova remnant in He ii λ4686, Hβ, Hei λ5876, [O i] λλ6300, 6364, [N ii] λλ6548, 6583,
sulfur λλ6716, 6731, sulfur λ9069, and Carbon i λλ9823, 9850. We present both raw and flux-calibrated emission-line
images. Arrays of 19,440 photoionization models, with extensive input abundance ranges, were matched pixel by
pixel to the calibrated data in order to derive corresponding element abundance or mass-fraction distributions for helium, carbon, nitrogen, oxygen, and sulfur. These maps show distinctive structure, and they illustrate regions
of gas in which various stages of nucleosynthesis have apparently occurred, including the CNO cycle, helium
burning, carbon burning, and oxygen burning. It is hoped that the calibrated observations and chemical abundance
distribution maps will be useful for developing a better understanding of the precursor star evolution and the
supernova explosive process.
Key words: ISM: individual objects (Crab Nebula) – ISM: supernova remnants – nuclear reactions,
nucleosynthesis, abundances – supernovae: individual (SN 1054)

3.3. Mass-fraction Plots
The resultant element abundance plots for the two density paradigm cases described above are shown in Figures 5 and 6.
Helium is presented in terms of its overall mass percentage in the emitting gas, whereas other elements are given as rough multiples of their solar mass fractions.

We note that the helium mass fraction maps are virtually indistinguishable for the two input density regimes.

Helium comprises about 40% to >90% of the emitting gas in different regions, with an overall derived distribution very much like that reported by Uomoto & MacAlpine (1987). There is an area with relatively low helium in the north, possibly indicative of an ambient interstellar cloud (Morrison & Roberts 1985; Fesen & Gull 1986). In addition, the roughly east–west high-helium band or torus (see also Lawrence at al. 1995) stands out as a prominent feature.

For the two types of models illustrated, the carbon, nitrogen, and oxygen mass-fraction maps are similar in terms of overall structure, with some quantitative differences especially for carbon. On the other hand, the sulfur maps show some notable variation. As discussed previously, double valuing tends to occur for matching S ii/Hβ emission and sulfur abundance, resulting in the lower possible abundance being selected by our algorithm. Therefore, the sulfur maps derived from S ii emission show some unrealistically low mass fractions. We do not know which (if either) set of input density assumptions is more appropriate for Crab Nebula emitting gas, and we will arbitrarily concentrate on the constant nuclear density maps (Figure 6) in further discussion below.

Next, we consider carbon, which is a product of helium fusion. The distribution map of Figure 6(b) shows a wide range of carbon mass fraction, from roughly solar to more than 30 times solar. This is consistent with the results of MS, who demonstrated how the strong observed C i λλ9823, 9850 doublet arises from electron collisional excitation in gas with very high helium abundance and who then used spectroscopic measures along with photoionization simulations to derive carbon concentrations more than 10 times solar in parts of the Crab Nebula. As shown by the ionization, temperature, and density diagrams in Figures 2, 3, 4, and 5 of MS, very high helium abundance causes rapid depletion, near the face of a cloud, of ionizing photons with energy above 24.6 eV, the ionization potential of He0. Because C+ has a comparable ionization potential and that for C0 is below 13.6 eV, the dominant ionization stage for carbon is C+. Recombination of C+ to C0 in the warm He0 and H+ zone leads to strong collisionally excited Ci λλ9823, 9850 emission, which becomes more pronounced for higher helium abundance as illustrated in Figure 7 (from Katz 2011).

We note that the carbon mass-fraction distribution does not exactly follow the observed Ci flux of Figure 3(h) or the Ci/Hβ map of Figure 4(f). This can be understood from examination of the helium distribution in Figure 6(a) and consideration of Figure 7. Regions with relatively lower Ci emission and lower helium abundance may actually contain more carbon compared with regions of higher C i emission and higher helium abundance.


Helium abundance is not the only reason why Ci λλ9823, 9850 emission is stronger in the Crab Nebula than in other types of astronomical objects. Because of effects on photon mean free paths and ionization transition zone widths, the ionization parameter and gas density can also play roles in producing this emission, as illustrated in Figure 8 (from Katz 2011). Planetary nebulae or Hii regions may be characterized by gas with logU of the order of 0 (e.g., Becerra-Davila et al. 2001), so we would not expect strong C i/Hα from them, even if the helium abundance were high. In addition, for expected densities of 106 cm−3 or higher, C i emission should not stand out in a Seyfert galaxy or quasar spectrum.

As shown in Figures 3(e) and 4(c), N ii λλ6548, 6583 emission is strong in the northern part of the nebula, in accordance with the long-slit spectroscopic findings of MacAlpine et al. (1996). Resultant derived elevated nitrogen abundances could have arisen from the CNO cycle, with relatively low helium in that region indicative of interaction with an ambient cloud (see above). MS showed how high helium abundance is conducive to producing strong N ii emission, so lower helium abundance in the north (see Figure 6(a)) also leads to higher derived nitrogen abundance for a measured N ii intensity. According to Figure 6(c), the nitrogen abundance tends to be lower in those parts of the nebula where a lot of carbon exists, probably as a result of 14N(α,γ )18F(β−ν)18O(α,γ )22Ne processing which would be expected to accompany helium burning (Nomoto 1985).

Infrared neon lines have been measured in the Crab Nebula by Temim et al. (2006). They reported strong emission from Ne ii 12.8μm and Ne iii 15.5μm near the center of the nebula, where we find relatively low nitrogen abundance. Furthermore, MacAlpine et al. (2007) found an inverse relation between their measured N ii] λ6583 and the Temim et al. measured Ne ii 12.8μm for a particular position.

Finally,we note that the apparent high nitrogen abundance around some edges of the nebula may be real, or it could be due in part to our use of Nii/Hβ ratios for regions with very weak Hβ emission (compare Figures 3(b), 3(e), and 4(c)).

Oxygen: Turning our attention now to the observed Oi λλ6300, 6364 fluxes, Oi/Hβ ratios, and oxygen mass-fraction distributions of Figures 3(d), 4(b), and 6(d), respectively, we see strong emission and high oxygen abundance in the central east–west band of the nebula, including in outlying parts of the high-helium torus region. Oxygen could arise from helium or carbon burning.

From examination of element overlaps (or lack thereof) in the Woosley & Heger (2007) 10M stellar core mass-fraction diagram, it may seem odd that some of the highest oxygen abundances in Figure 6(d) appear to coincide with regions where the helium abundance is also quite high. However, this apparent anomaly could result from gas mixing in the Crab Nebula or from a combination of different gas regimes along our line of sight. Mixing and averaging of emission along sight lines may also help to explain why we do not derive oxygen mass fractions as high as the maximum in the Woosley & Heger mass cut simulation. In addition, as noted in Section 3.1 above, for O i emission, consideration of spherical geometry cloudlets immersed in the synchrotron radiation field could lead to a decrease of as much as 40% in the computed O i/Hβ ratio and to a corresponding increase in the derived oxygen mass fraction for a given pixel. Going to a cylindrical filamentary geometry would have somewhat less of an effect.

Sulfur: Finally, we consider the S ii λλ6716, 6731 and S iii λ9069 emission in Figures 3(f), 3(g), 4(d), and 4(e), along with the S iii-derived (see previous discussion) sulfur mass-fraction map of Figure 6(f). The general S ii emission features are similar to those in MacAlpine et al. (1989) and Charlebois et al. (2010). The raw S iii image here has less signal-to-noise, is more dominated by continuum, and shows fewer prominent features compared with the raw S ii image. However, the flux-calibrated and continuum-subtracted images look very much alike. We note that S iii λ9069 was chosen for this investigation, rather than the stronger line at λ9531, because of telluric water vapor absorption in the region of the latter (see Stevenson 1994; Vermeij et al. 2002; MacAlpine et al. 2007).

As illustrated in Figure 6(f), high sulfur abundance regions tend to avoid some western parts of the nebula, being concentrated primarily to the east, as might be understood in terms of off-center oxygen ignition (see Woosley & Weaver 1986). The sulfur concentrations appear to avoid regions with the highest helium and oxygen abundances, instead occupying the apparent loop-like structures. Fairly high sulfur in the southeast edge filaments could be real, or it may result from weak Hβ in the S iii/Hβ ratios used for comparison with the model computations.

4. SUMMARY
We have presented new raw and flux-calibrated, continuum subtracted emission-line images of the Crab Nebula in
He ii λ4686, Hβ, He i λ5876, O i λλ6300, 6364, N ii λλ6548, 6583, S ii λλ6716, 6731, S iii λ9069, and C i λλ9823, 9850.


Ratios of line images to Hβ were compared with an extensive grid of photoionization simulations in order to derive element mass-fraction maps for helium, carbon, nitrogen, oxygen, and sulfur. These distributions should be considered to be somewhat simplified approximations in the sense that plane-parallel geometry was assumed, along with global assumptions regarding ionizing radiation and gas physical conditions. It may be possible in future studies to divide the nebula into different regions with separate assumptions, but we believe from considering various parametric schemes that the results presented are representative of the Crab Nebula’s general characteristics.

Although there has apparently been mixing physically as well as observationally along the line of sight, and also pulsar wind-driven material, the element distributions are distinct and informative. They illustrate regions of gas in which various stages of nucleosynthesis have occurred, including the CNO cycle, helium burning, carbon burning, and oxygen burning. It is hoped that the calibrated observations and chemical abundance distribution maps will be useful for developing a better understanding of the precursor star evolution and the supernova explosive process.Work currently underway will extend this investigation to derive actual mass distributions and estimates of overall masses for the various elements.

This work was supported by Trinity University and the endowed Charles A. Zilker Chair position. We also thank the staffs of theMcDonald Observatory and theMDM Observatory for providing technical assistance.

Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Neon, Sulfur AND Water Vapor!

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articles.adsabs.harvard.edu/pdf/1984ApJ...281..644H

1984ApJ. . .281 . .644H
The Astrophysical Journal, 281:644-649, 1984 June 15 © 1984. The American Astronomical Society. All rights reserved. Printed in U.S.A.
THE UNUSUAL NICKEL/IRON ABUNDANCE RATIO IN THE CRAB NEBULA FILAMENTS
Richard B. C. Henry University of Delaware Received 1983 October 14; accepted 1983 December 20

ABSTRACT
I have employed recently published line strengths of [Ni n] À131S and [Fe n] A8617 at 12 positions in the
Crab nebula in order to infer a Ni/Fe abundance ratio at each location. Ni/Fe is found to exceed the solar value by an order of magnitude in each case. An analysis of data for one position in the Orion nebula yields similar results. The following possible explanations for these findings are discussed: (1) both objects contain material which has been processed nucleosynthetically under neutron-rich conditions; (2) Fe is being preferentially depleted through grain formation in both objects; (3) large errors exist in the atomic data; and (4) certain physical processes such as charge exchange or dielectronic or radiative recombination affect the ionization balance or the populations of the upper levels of the relevant transitions in a manner not accounted for in the abundance analysis. The most likely explanation for the Ni/Fe puzzle would appear to be either a large dielectronic recombination or charge exchange rate for production of Ni+. On the other hand, preferential grain depletion of Fe, a hypothesis recently put forth in several papers, can almost certainly be ruled out, as can the presence of neutron-rich nucleosynthesized material.

Subject headings: atomic processes — nebulae: abundances — nebulae: Crab Nebula —
nebulae: Orion Nebula — nebulae: supernova remnants

I. INTRODUCTION
The filaments of the Crab nebula are composed primarily ofstellar debris from SN 1054, and thus the determination of the relative chemical abundances in the gas is important for deducing the chemical structure of the stellar precursor as well as the dynamics of the explosion. A discussion of the relative abundances of many of the elements lighter than Fe in the Crab filaments may be found in Woltjer (1958), Davidson(1973,1978,1979), Davidson et al (1982), Contini, Kozlovsky, and Shaviv (1977), Henry and MacAlpine (1982, hereafter HM), and Péquignot and Dennefeld (1983). Although Davidson (1979) estimated the Fe mass fraction in the nebula to be roughly solar based on an analysis employing weak[Fe m] 24658 emission at several filament positions, more detailed work for Fe-peak elements has been difficult to carry out. This is largely due to a lack of understanding of the ionization and temperature structure of the filamentary gas, observations of useful emission lines representing severalionization stages, and, in some cases, necessary atomic data.

Recently, however, Henry, MacAlpine, and Kirshner (1984, hereafter HMK) observed 14 positions in the Crab nebula in the near-infrared and used “average” line strengths of [Ni ii] 27378 and [Fe n] 28617, two lines presumably formed in the same region of a filament, plus atomic data from Nussbaumer and Storey (1980, 1982) to infer that the relative abundances of Ni and Fe by number are 18 times and 0.5 times their solar values, respectively. This implies a Ni/Fe ratio by number of 36 times the solar level. Dennefeld and Péquignot (1983), in reporting similar observations for one Crab filament, found a Ni/Fe ratio slightly higher than HMK’s but of the same order of magnitude.

Because of the significance of these findings in terms of understanding Fe-peak abundances in young supernova remnants, where the visible material is mostly stellar debris, it is important to verify the above results for Ni/Fe in the Crab by considering the data in greater detail. Therefore, using HMK’s data for 12 positions in the Crab nebula, I have calculated the abundances of Ni and Fe at each location. To test the abundance determination method I have applied it to the Orion nebula, using data available in the literature. In this paper, the results of these calculations, along with a detailed assessment ofthe various explanations which might be invoked to interpret the results, are presented. Section II contains a description ofthe methods employed to estimate the Ni and Fe abundances, §§ III and IV contain the results and a discussion, respectively, and § V is a summary of the findings.

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www.actforlibraries.org/crab-nebula/

Crab Nebula

Physical Science

The Crab Nebula is one of the most intensely studied and most beautiful of objects to be found in the night sky. This beautifully coloured swirling cloud of interstellar gas can easily be seen with binoculars and low grade telescopes. It is so beautiful that it has inspired many amateur astronomers to pursue their hobby.

The Crab Nebula extends over an area of sky approximately one fifth of that of a full moon. Within this area of sky observers can see an extraordinary complex web of red, brown and white filaments. A turquoise blue light radiates from the gasps between the filaments. Although the nebula was first observed by John Bevis in 1731 it was not named as the Crab Nebula until 1848, In 1848 William Parsons, the third Earl of Rosse, made a sketch of the nebula. He thought that it looked like a crab.

Although beautiful, and often photographed as a feature for glossy, coffee table books about astronomy it has taken astronomers a long time to understand the processes at work in the Crab Nebula. Their understanding has developed from a series of scientific clues.

In the early twentieth century scientists identified that the nebula was evolving. Two photos taken of the nebula at an interval of two years were not identical. The nebula is thought to be some 6 ,300 light years from Earth with a diameter of about 1.3 light years. Changes that are discernable on this scale from Earth must be the product of very high energy events.

The exact location of the Crab Nebula is intriguing. It is thought to lie within one of outer spirals of the galaxy and is thought to be in the form of a squat sphere of gas expanding outwards from a central source. The central point is thought to be a the same location as an event witnessed by Chinese and Arab astronomers in 1056 when the astronomers saw a very bright object in the sky. Moreover, changes seen in the twentieth century photographic plates imply that the nebula has expanded from a central point dating from the middle of the 11th century.

Spectroscopic analysis has identified that the colourful arms of the nebula are composed of ionized helium, hydrogen along with molecules of carbon, oxygen, nitrogen, iron, neon and sulphur.

In 1953 Josif Shklovsky demonstrated that the mysterious blue glow found within the nebula was the product of electrons decelerating in an intense magnetic field.

More detailed spectroscopic analysis has shown that the Crab Nebula is a rich source of radio and gamma waves. The radio waves appear to be pulsed and are emitted at regular intervals of 33 milliseconds. The discovery of the regular radio emissions in 1967 was so enigmatic that some thought that an extra-terrestrial life form was signalling from within the nebula

Unravelling these clues has led scientists to the forefront of theories of solar evolution and decay. The chemical composition of the gas clouds can be explained by nucleo-synthesis. Elements up to the atomic weight of iron are produced by the nuclear fusion reactions which power stars. During the course of the reaction the energy released by nuclear fusion is able to offset the gravitational forces which encourage a star to collapse in on itself. However, when the fuel is extinguished, gravitational forces dominate and a star can implode. This is thought to have happened to a central star on the site of the Crab Nebula in 1056. Depending upon the mass of the star the collapse can be so rapid that the imploding gas builds up a tremendous temperature and pressure causing the collapse to stall and the gas to explode at high velocity back into space. Sometimes a similar effect is seen if too much water is forced =down a bathroom plughole. The explosion can be very rapid and is almost certainly the cause of the 1056 observation.

The puzzles of the strong magnetic field, gamma ray and regular radio wave emissions can be solved by proposing that the star continues to collapse. Having shed some of the incoming gas, pressures and densities continue to increase. Conditions become so intense that protons decay by nuclear reaction into neutron and neutrinos. Ultimately a very compact core of neutrons is formed containing the mass of the star in a sphere of just 20 kilometres in radius. A neutron star of this type is thought to lie at the heart of the Crab Nebula.

The regular radio signal that emanates from the Crab Nebula is an example of a pulsar. The exact reasons why neutron stars emit radio and gamma rays is unclear, hover the radio waves are believed to be omitted along the magnetic access of the neutron star. Neutron stars are known to spin vigorously, The reason for this is similar to that of a pirouetting dancer who pulls in her arms. To conserve angular momentum an object of smaller radius has to spin faster. When the spinning neutron star points in the direction of Earth a radio burst is transmitted in our direction. This is the origin of the 33 milli-second signal.

Although not the first pulsar to be discovered the discovery of the 33 millisecond radio signal from the Crab Nebula in 1968 was a milestone event in the unravelling of the Crab Nebula and super nova science.

www.actforlibraries.org/interesting-facts-about-the-crab-nebula/

Interesting Facts about the Crab Nebula

Physical Science

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus and possibly the most intensely studied bright nebula in the Universe.

The Crab Nebula is approximately 6,500 light years from Earth, has an absolute magnitude (visible brightness) of 8.4 and is approximately 10 light years in diameter. To put its diameter into perspective, if the Sun was the size of a basketball, the Crab Nebula would be the size of Earth.

At the centre of the nebula is the Crab Pulsar, a neutron star approximately 30 km across and spinning at about 30 revolutions every second.

According to historical records from 1054, the supernova explosion that resulted in the formation of the Crab Nebula was seen on Earth beginning on July 4th, by Chinese and Arab astronomers. Recorded as a “guest star” by Chinese astronomers, it was visible in daylight for 23 days and at night for almost 2 years. The explosion was described by Yang Wei-te, the court astronomer to the Sung emperor, as yellow in colour. The event was probably also recorded by Anasazi Indian artists, in present day Arizona and New Mexico, as findings in Navaho Canyon and White Mesa indicate. In addition, Mimbres Indian art from New Mexico has also been found which possibly depicts the supernova. There are no records of observation at the time by Europeans.

The discovery of the object as a nebula is attributed to John Bevis, an English physician and amateur astronomer, who made the discovery in 1731 and added it to his sky atlas, Uranographia Britannica. Some 27 years later, on August 28, 1758, Charles Messier independently found a “nebulosity above the southern horn of Taurus…”, whilst he was looking for the first predicted return of Halley’s Comet. Messier at first thought it was a comet but realised that it had no apparent motion. It was this discovery that led to Messier compiling his famous catalogue of nebulae and star clusters so that others would not confuse them with comets “just beginning to shine”. This is the origin of the designation of M1, number 1 in Messier’s catalogue. Messier later acknowledged the original discovery made by John Bevis after learning of it in a letter of June 10, 1771.

The Crab Nebula got its most familiar name in 1840 when William Parsons, the Third Earl of Rosse, observed the nebula using a 36 inch telescope and created a drawing that he thought looked like a crab. The 36 inch telescope however did not allow Parsons to fully resolve the filaments, that coloured web of hot gas that permeates the nebula. When in 1848 Parsons again observed the object with a 72 inch telescope, it allowed him to see the nebula in greater detail. Although he noted that his earlier drawings did not represent the true structure of the nebular, the name Crab Nebular had already become familiar.

The Crab Nebular is part of a class of objects known as Supernova Remnants (SNRs), that are the result of a large star going through a phase of its evolution known as a supernova. This phase occurs when the star no longer has enough fuel to keep from collapsing onto itself and it explodes in a violent surge of energy. The outer part of the star is driven into space, forming the remnant that can be observed today. It has been suggested that had the Crab Supernova occurred within 26 light years of the Sun, most living organisms on Earth’s surface would have been destroyed, as the resultant radiation would have caused the breakdown of Earth’s ozone layer.

The filaments of the Crab consist of the material ejected in the supernova explosion, spread over a distance approximately 10 light years in diameter, which is still rapidly expanding at the incredible velocity of 1,800 km/sec. These filaments are composed mainly of ionized helium and hydrogen together with oxygen, carbon, iron, nitrogen, neon and sulphur. These filaments are the remnants from the outer layers of the former star, the progenitor, whilst the inner blue coloured nebula emits light consisting of highly polarized synchrotron radiation which is emitted by high-energy electrons in a strong magnetic field. This explanation was first proposed by the Soviet astronomer J. Shklovsky in 1953.

In 1968, the Crab Pulsar was detected as a pulsating radio source at the centre of the nebula by astronomers of the Arecibo Observatory 300 meter radio telescope in Puerto Rico. It has been established that this pulsar is a rapidly rotating neutron star which rotates at around 30 times per second. This neutron star is an extremely dense object with more density than an atomic nucleus, concentrating more than one solar mass in a volume of 30 kilometres across. Its rotation is slowly decelerating by magnetic interaction with the nebula, providing the energy source which produces the shining effect of the nebula. It has been estimated that this energy source is 100,000 times more powerful that the Sun.

Astronomers are aware of around 1000 pulsars, this number growing almost daily due to radio telescope discoveries. However, the Crab pulsar is one of the youngest and most energetic pulsars known. While some pulsars have been observed to pulse in X-rays and gamma-rays, the Crab pulsar seems to pulse in almost every wavelength, pulsing in radio, optical, X-rays and gamma-rays and its nebula is also visible over that very broad range of wavelengths.

On January 8, 2007, a team of astronomers announced evidence that the Crab Pulsar may have four magnetic poles, rather than the usual two. It has been suggested that the two additional poles may have been “frozen” into the pulsar during its formation in a supernova explosion. Normally a pulsar beam from only one pole would be observed, although a weaker second signal can sometimes be detected if the beam from the other pole is pointing in Earth’s direction when it comes into view. The Crab pulsar is known to emit weaker secondary pulses, which indicate that the primary and secondary pulses are different, something that would be difficult to explain as coming from opposite magnetic poles. This has led to some astronomers suggesting that the secondary pulses are related to an additional pair of magnetic poles.

On April 12, 2011, a blast of gamma rays, the highest-energy light in the Universe, was detected being emitted by the Crab nebula. The cause of the gamma ray flare, described at the Third Fermi Symposium in Rome, mystified astronomers.

From 1054 AD to the present day, the Crab Nebula continues to fascinate.

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www.nasa.gov/jpl/herschel/crab-nebula-20131212


This image shows a composite view of the Crab nebula, an iconic supernova remnant in our Milky Way galaxy, as viewed by the Herschel Space Observatory and the Hubble Space Telescope.
Credits: ESA/Herschel/PACS/MESS Key Programme Supernova Remnant Team

Astronomers have discovered a rare chemical pairing in the remains of an exploded star, called the Crab nebula. A gas thought to be a loner has made a "friend," linking up with a chemical partner to form a molecule. The discovery, made with the Herschel space observatory, a European Space Agency mission with important NASA contributions, will help scientists better understand supernovas, the violent deaths of massive stars.

The unexpected find involves a noble gas called Argon, named for its chemical aloofness after the Greek word for "inactive." Noble gases, which also include helium and neon among others, rarely engage in chemical reactions. They prefer to go it alone.

A new study, led by Michael Barlow from University College London, United Kingdom, and based on spectral data from Herschel, has found the first evidence of such a noble gas-based compound in space, a molecule called argon hydride. The results are published in the journal Science.

"The strange thing is that it is the harsh conditions in a supernova remnant that seem to be responsible for some of the argon finding a partner with hydrogen,” said Paul Goldsmith of NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

"This is not only the first detection of a noble-gas based molecule in space, but also a new perspective on the Crab nebula. Herschel has directly measured the argon isotope we expect to be produced via explosive nucleosynthesis in a core-collapse supernova, refining our understanding of the origin of this supernova remnant,” concludes Göran Pilbratt, Herschel project scientist at the European Space Agency.

Read the full ESA news release at:

sci.esa.int/herschel/53332-herschel-spies-active-argon-in-crab-nebula/ .

Herschel is a European Space Agency mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at JPL. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information is online at www.herschel.caltech.edu , www.nasa.gov/herschel and www.esa.int/SPECIALS/Herschel .

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VERITAS Crab Nebula Announcement
Photo by josefrancisco.salgado on flickr
· · · Photo composite made for the VERITAS announcement in Science Magazine. Credit: José Francisco Salgado. Based on images by M SubbaRao, S Criswell, B Humensky, JF Salgado, Hubble/Spitzer/Chandra

We report the detection of pulsed gamma rays from the Crab pulsar at energies above 100 giga–electron volts (GeV) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) array of atmospheric Cherenkov telescopes.

The detection cannot be explained on the basis of current pulsar models.

The photon spectrum of pulsed emission between 100 mega–electron volts and 400 GeV is described by a broken power law that is statistically preferred over a power law with an exponential cutoff. It is unlikely that the observation can be explained by invoking curvature radiation as the origin of the observed gamma rays above 100 GeV. Our findings require that these gamma rays be produced more than 10 stellar radii from the neutron star. [VERITAS Education Site]

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I am amazed at how similar the Crab Nebula is to Centaurus a!

Crab Nebula


Centaurus a


The early universe must have been so compact the first stars were galaxy size and almost immediately exploded to become galaxies - just as supernovas do today at a much smaller scale!