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M1 Galaxy - The Crab Nebula
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. The Crab Nebula lies about 6,500 light-years away in the constellation Taurus.
Image Credit: Detlef Hartmann
The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. The now-current name is due to William Parsons, 3rd Earl of Rosse, who observed the object in 1840 using a 36-inch telescope and produced a drawing that looked somewhat like a crab. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. The nebula was the first astronomical object identified 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 source in the sky, with measured flux extending to above 10 TeV. The nebula's radiation allows for the detailed studying 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.
The inner part of the nebula is a much smaller pulsar wind nebula that appears as a shell surrounding the pulsar. Some sources consider the Crab Nebula to be an example of both a pulsar wind nebula as well as a supernova remnant, while others separate the two phenomena based on the different sources of energy production and behaviour. For the Crab Nebula, the divisions are superficial but remain meaningful to researchers and their lines of study.
Modern understanding that the Crab Nebula was created by a supernova dates to 1921, when Carl Otto Lampland announced he had seen changes in its structure. This eventually led to the conclusion that the creation of the Crab Nebula corresponds to the bright SN 1054 supernova recorded by Chinese astronomers in AD 1054. There is also a 13th-century Japanese reference to this "guest star" in Meigetsuki.
The event was long considered unrecorded in Islamic astronomy, but in 1978 a reference was found in a 13th-century copy made by Ibn Abi Usaibia of a work by Ibn Butlan, a Nestorian Christian physician active in Baghdad at the time of the supernova.
The Crab Nebula was first identified in 1731 by John Bevis. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet. Messier catalogued it as the first entry in his catalogue of comet-like objects; in 1757, Alexis Clairaut reexamined the calculations of Edmund Halley and predicted the return of Halley's Comet in late 1758. The exact time of the comet's return required the consideration of perturbations to its orbit caused by planets in the Solar System such as Jupiter, which Clairaut and his two colleagues Jérôme Lalande and Nicole-Reine Lepaute carried out more precisely than Halley, finding that the comet should appear in the constellation of Taurus. It is in searching in vain for the comet that Charles Messier found the Crab nebula, which he at first thought to be Halley's comet. After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet. Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets.
William Herschel observed the Crab Nebula numerous times between 1783 and 1809, but it is not known whether he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. After several observations, he concluded that it was composed of a group of stars. The 3rd Earl of Rosse observed the nebula at Birr Castle in 1844 using a 36-inch (0.9 m) telescope, and referred to the object as the "Crab Nebula" because a drawing he made of it looked like a crab. He observed it again later, in 1848, using a 72-inch (1.8 m) telescope and could not confirm the supposed resemblance, but the name stuck nevertheless.
Connection to SN 1054
In 1913, when Vesto Slipher registered his spectroscopy study of the sky, the Crab Nebula was again one of the first objects to be studied. In the early twentieth century, the analysis of early photographs of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900 years ago. Historical records revealed that a new star bright enough to be seen in the daytime had been recorded in the same part of the sky by Chinese astronomers in 1054.
Changes in the cloud, suggesting its small extent, were discovered by Carl Lampland in 1921. That same year, John Charles Duncan demonstrated that the remnant is expanding, while Knut Lundmark noted its proximity to the guest star of 1054.
In 1928, Edwin Hubble proposed associating the cloud to the star of 1054, an idea which remained controversial until the nature of supernovae was understood, and it was Nicholas Mayall who indicated that the star of 1054 was undoubtedly the supernova whose explosion produced the Crab Nebula. The search for historical supernovae started at that moment: seven other historical sightings have been found by comparing modern observations of supernova remnants with astronomical documents of past centuries. Given its great distance, the daytime "guest star" observed by the Chinese could only have been a supernova—a massive, exploding star, having exhausted its supply of energy from nuclear fusion and collapsed in on itself.
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. Thanks to the recorded observations of Far Eastern and Middle Eastern astronomers of 1054, Crab Nebula became the first astronomical object recognized as being connected to a supernova explosion.
In the 1960s, because of the prediction and discovery of pulsars, the Crab Nebula again became a major centre of interest. It was then that Franco Pacini predicted the existence of the Crab Pulsar for the first time, which would explain the brightness of the cloud. The star was observed shortly afterwards in 1968. The discovery of the Crab pulsar, and the knowledge of its exact age (almost to the day) allows for the verification of basic physical properties of these objects, such as characteristic age and spin-down luminosity, the orders of magnitude involved (notably the strength of the magnetic field), along with various aspects related to the dynamics of the remnant. The role of this supernova to the scientific understanding of supernova remnants was crucial, as no other historical supernova created a pulsar whose precise age we can know for certain. The only possible exception to this rule would be SN 1181 whose supposed remnant, 3C58, is home to a pulsar, but its identification using Chinese observations from 1181 is sometimes contested.
In visible light, the Crab Nebula consists of a broadly oval-shaped mass of filaments, about 6 arcminutes long and 4 arcminutes wide (by comparison, the full moon is 30 arcminutes across) surrounding a diffuse blue central region. In three dimensions, the nebula is thought to be shaped like a prolate spheroid. The filaments are the remnants of the progenitor star's atmosphere, and consist largely of ionised helium and hydrogen, along with carbon, oxygen, nitrogen, iron, neon and sulfur. The filaments' temperatures are typically between 11,000 and 18,000 K, and their densities are about 1,300 particles per cm3.
In 1953 Iosif Shklovsky proposed that the diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving motion of electrons in a magnetic field. The radiation corresponded to electrons moving at speeds up to half the speed of light. Three years later the theory was confirmed by observations. In the 1960s it was found that the source of the curved paths of the electrons was the strong magnetic field produced by a neutron star at the centre of the nebula.
Even though the Crab Nebula is the focus of much attention among astronomers, its distance remains an open question, owing to uncertainties in every method used to estimate its distance. In 2008, the consensus was that its distance from Earth is 2.0 ± 0.5 kpc (6,500 ± 1,600 ly). Along its longest visible dimension, it thus measures about 4.1 ± 1 pc (13 ± 3 ly) across.
The Crab Nebula currently is expanding outward at about 1,500 km/s (930 mi/s). Images taken several years apart reveal the slow expansion of the nebula, and by comparing this angular expansion with its spectroscopically determined expansion velocity, the nebula's distance can be estimated. In 1973, an analysis of many methods used to compute the distance to the nebula had reached a conclusion of about 1.9 kpc (6,300 ly), consistent with the currently cited value.
The Crab Pulsar itself was discovered in 1968. Tracing back its expansion (assuming a constant decrease of expansion speed due to the nebula's mass) yielded a date for the creation of the nebula several decades after 1054, implying that its outward velocity has decelerated less than assumed since the supernova explosion. This reduced deceleration is believed to be caused by energy from the pulsar that feeds into the nebula's magnetic field, which expands and forces the nebula's filaments outward.
Estimates of the total mass of the nebula are important for estimating the mass of the supernova's progenitor star. The amount of matter contained in the Crab Nebula's filaments (ejecta mass of ionized and neutral gas; mostly helium) is estimated to be 4.6±1.8 Mâ˜‰.
One of the many nebular components (or anomalies) of the Crab Nebula is a helium-rich torus which is visible as an east-west band crossing the pulsar region. The torus composes about 25% of the visible ejecta. However, it is suggested by calculation that about 95% of the torus is helium. As yet, there has been no plausible explanation put forth for the structure of the torus.
At the center of the Crab Nebula are two faint stars, one of which is the star responsible for the existence of the nebula. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual. The region around the star was found to be a strong source of radio waves in 1949 and X-rays in 1963, and was identified as one of the brightest objects in the sky in gamma rays in 1967. Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars to be discovered.
Pulsars are sources of powerful electromagnetic radiation, emitted in short and extremely regular pulses many times a second. They were a great mystery when discovered in 1967, and the team who identified the first one considered the possibility that it could be a signal from an advanced civilization. However, the discovery of a pulsating radio source in the centre of the Crab Nebula was strong evidence that pulsars were formed by supernova explosions. They now are understood to be rapidly rotating neutron stars, whose powerful magnetic field concentrates their radiation emissions into narrow beams.
The Crab Pulsar is believed to be about 28–30 km (17–19 mi) in diameter; it emits pulses of radiation every 33 milliseconds. Pulses are emitted at wavelengths across the electromagnetic spectrum, from radio waves to X-rays. Like all isolated pulsars, its period is slowing very gradually. Occasionally, its rotational period shows sharp changes, known as 'glitches', which are believed to be caused by a sudden realignment inside the neutron star. The energy released as the pulsar slows down is enormous, and it powers the emission of the synchrotron radiation of the Crab Nebula, which has a total luminosity about 75,000 times greater than that of the Sun.
The pulsar's extreme energy output creates an unusually dynamic region at the centre of the Crab Nebula. While most astronomical objects evolve so slowly that changes are visible only over timescales of many years, the inner parts of the Crab Nebula show changes over timescales of only a few days. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the bulk of the nebula, forming a shock front. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar to well out into the main body of the nebula.
The star that exploded as a supernova is referred to as the supernova's progenitor star. Two types of stars explode as supernovae: white dwarfs and massive stars. In the so-called Type Ia supernovae, gases falling onto a 'dead' white dwarf raise its mass until it nears a critical level, the Chandrasekhar limit, resulting in a runaway nuclear fusion explosion that obliterates the star; in Type Ib/c and Type II supernovae, the progenitor star is a massive star whose core runs out of fuel to power its nuclear fusion reactions and collapses in on itself, releasing gravitational potential energy in a form that blows away the star's outer layers. The presence of a pulsar in the Crab Nebula means that it must have formed in a core-collapse supernova; Type Ia supernovae do not produce pulsars.
Theoretical models of supernova explosions suggest that the star that exploded to produce the Crab Nebula must have had a mass of between 9 and 11 Mâ˜‰. Stars with masses lower than 8 Mâ˜‰ are thought to be too small to produce supernova explosions, and end their lives by producing a planetary nebula instead, while a star heavier than 12 Mâ˜‰ would have produced a nebula with a different chemical composition from that observed in the Crab Nebula. Recent studies, however, suggest the progenitor could have been a super-asymptotic giant branch star in the 8 to 10 Mâ˜‰ range that would have exploded in an electron-capture supernova.
A significant problem in studies of the Crab Nebula is that the combined mass of the nebula and the pulsar add up to considerably less than the predicted mass of the progenitor star, and the question of where the 'missing mass' is, remains unresolved. Estimates of the mass of the nebula are made by measuring the total amount of light emitted, and calculating the mass required, given the measured temperature and density of the nebula. Estimates range from about 1–5 Mâ˜‰, with 2–3 Mâ˜‰ being the generally accepted value. The neutron star mass is estimated to be between 1.4 and 2 Mâ˜‰.
The predominant theory to account for the missing mass of the Crab Nebula is that a substantial proportion of the mass of the progenitor was carried away before the supernova explosion in a fast stellar wind, a phenomenon commonly seen in Wolf-Rayet stars. However, this would have created a shell around the nebula. Although attempts have been made at several wavelengths to observe a shell, none has yet been found.
Transits by Solar System bodies
The Crab Nebula lies roughly 1.5 degrees away from the ecliptic—the plane of Earth's orbit around the Sun. This means that the Moon—and occasionally, planets—can transit or occult the nebula. Although the Sun does not transit the nebula, its corona passes in front of it. These transits and occultations can be used to analyse both the nebula and the object passing in front of it, by observing how radiation from the nebula is altered by the transiting body.
Lunar transits have been used to map X-ray emissions from the nebula. Before the launch of X-ray-observing satellites, such as the Chandra X-ray Observatory, X-ray observations generally had quite low angular resolution, but when the Moon passes in front of the nebula, its position is very accurately known, and so the variations in the nebula's brightness can be used to create maps of X-ray emission. When X-rays were first observed from the Crab Nebula, a lunar occultation was used to determine the exact location of their source.
The Sun's corona passes in front of the Crab Nebula every June. Variations in the radio waves received from the Crab Nebula at this time can be used to infer details about the corona's density and structure. Early observations established that the corona extended out to much greater distances than had previously been thought; later observations found that the corona contained substantial density variations.
Very rarely, Saturn transits the Crab Nebula. Its transit in 2003 was the first since 1296; another will not occur until 2267. Observers used the Chandra X-ray Observatory to observe Saturn's moon Titan as it crossed the nebula, and found that Titan's X-ray 'shadow' was larger than its solid surface, due to absorption of X-rays in its atmosphere. These observations showed that the thickness of Titan's atmosphere is 880 km (550 mi). The transit of Saturn itself could not be observed, because Chandra was passing through the Van Allen belts at the time.
- "M 1 – SuperNova Remnant". SIMBAD. Observatory of Strasbourg. Retrieved 12 February 2012.
- Kaplan, David L.; Chatterjee, S.; Gaensler, B. M.; Anderson, J. (2008). "A Precise Proper Motion for the Crab Pulsar, and the Difficulty of Testing Spin-Kick Alignment for Young Neutron Stars". The Astrophysical Journal. 677 (2): 1201–1215. arXiv:0801.1142 . Bibcode:2008ApJ...677.1201K. doi:10.1086/529026.
- Trimble, Virginia Louise (1973). "The Distance to the Crab Nebula and NP 0532". Publications of the Astronomical Society of the Pacific. 85 (507): 579. Bibcode:1973PASP...85..579T. doi:10.1086/129507. JSTOR 40675440.
- Hester, J. J. (2008). "The Crab Nebula: An Astrophysical Chimera". Annual Review of Astronomy and Astrophysics. 46: 127–155. Bibcode:2008ARA&A..46..127H. doi:10.1146/annurev.astro.45.051806.110608.
- Parsons, William (1844). "Observations on Some of the Nebulae". Philosophical Transactions of the Royal Society of London. 134. fig. 81, plate xviii, p. 321. doi:10.1098/rstl.1844.0012. JSTOR 108366.
- "Pulsar Wind Nebulae". Smithsonian Astrophysical Observatory. 4 November 2016. Retrieved 26 March 2017.
- Lampland, C. O. (1921). "Observed Changes in the Structure of the "Crab" Nebula (N. G. C. 1952)". Publications of the Astronomical Society of the Pacific. 33: 79–84. Bibcode:1921PASP...33...79L. doi:10.1086/123039. JSTOR 40710638.
- Katgert-Merkelijn, J.; Damen, J. (2000). "A short biography of Jan Hendrik Oort: 7. Crab Nebula". Leiden University Library. Archived from the original on 4 September 2014. Retrieved 9 March 2015.
- Usui, Tadashi (11 January 2007). "Why and how did a Japanese poet record the Supernova of AD 1054?". Archived from the original on 3 March 2016. Retrieved 4 March 2015.
- Fujiwara no Sadaie (c. 1200). Meigetsuki [Record of the Clear Moon].
- Green, David A.; Stephenson, F. Richard (2003). Weiler, K. W., ed. "The Historical Supernovae". Supernovae and Gamma Ray Bursters. Lecture Notes in Physics. Berlin: Springer. 598: 7–19. arXiv:astro-ph/0301603 . Bibcode:2003LNP...598....7G. doi:10.1007/3-540-45863-8_2.
- Mayall, Nicholas Ulrich (1939). "The Crab Nebula, a Probable Supernova". Astronomical Society of the Pacific Leaflets. 3 (119): 145. Bibcode:1939ASPL....3..145M.
- Duncan, John Charles (1921). "Changes Observed in the Crab Nebula in Taurus". Proceedings of the National Academy of Sciences. 7: 179–181. Bibcode:1921PNAS....7..179D. doi:10.1073/pnas.7.6.179.
- Collins, George W., II; Claspy, William P.; Martin, John C. (1999). "A Reinterpretation of Historical References to the Supernova of A.D. 1054". Publications of the Astronomical Society of the Pacific. 111 (761): 871–880. arXiv:astro-ph/9904285 . Bibcode:1999PASP..111..871C. doi:10.1086/316401.
- Setti, Giancarlo (2012). "Franco Pacini (1939–2012)". Bulletin of the American Astronomical Society. 44: 011. doi:10.3847/BAASOBIT2012011.
- Bietenholz, M. F. (July 2006). "Radio Images of 3C 58: Expansion and Motion of Its Wisp" (PDF). The Astrophysical Journal. 645 (2): 1180–1187. arXiv:astro-ph/0603197 . Bibcode:2006ApJ...645.1180B. doi:10.1086/504584.
- Fesen, R. A.; Kirshner, R. P. (1982). "The Crab Nebula. I – Spectrophotometry of the filaments". The Astrophysical Journal. 258 (1): 1–10. Bibcode:1982ApJ...258....1F. doi:10.1086/160043.
- Shklovskii, Iosif (1953). "On the Nature of the Crab Nebula's Optical Emission". Doklady Akademii Nauk SSSR. 90: 983. Bibcode:1957SvA.....1..690S.
- Burn, B. J. (1973). "A synchrotron model for the continuum spectrum of the Crab Nebula". Monthly Notices of the Royal Astronomical Society. 165 (4): 421. Bibcode:1973MNRAS.165..421B. doi:10.1093/mnras/165.4.421.
- Bietenholz, M. F.; Kronberg, P. P.; Hogg, D. E.; Wilson, A. S. (1991). "The expansion of the Crab Nebula". The Astrophysical Journal Letters. 373: L59–L62. Bibcode:1991ApJ...373L..59B. doi:10.1086/186051.
- Nemiroff, R.; Bonnell, J., eds. (27 December 2001). "Animation showing expansion from 1973 to 2001". Astronomy Picture of the Day. NASA. Retrieved 10 March 2010.
- Trimble, Virginia Louise (1968). "Motions and Structure of the Filamentary Envelope of the Crab Nebula" (PDF). Astronomical Journal. 73: 535. Bibcode:1968AJ.....73..535T. doi:10.1086/110658.
- Bejger, M.; Haensel, P. (2003). "Accelerated expansion of the Crab Nebula and evaluation of its neutron-star parameters". Astronomy and Astrophysics. 405 (2): 747–751. arXiv:astro-ph/0301071 . Bibcode:2003A&A...405..747B. doi:10.1051/0004-6361:20030642.
- Green, D. A.; Tuffs, R. J.; Popescu, C. C. (2004). "Far-infrared and submillimetre observations of the Crab nebula". Monthly Notices of the Royal Astronomical Society. 355 (4): 1315–1326. arXiv:astro-ph/0409469 . Bibcode:2004MNRAS.355.1315G. doi:10.1111/j.1365-2966.2004.08414.x.
- Fesen, Robert A.; Shull, J. Michael; Hurford, Alan P. (1997). "An Optical Study of the Circumstellar Environment Around the Crab Nebula". The Astronomical Journal. 113: 354–363. Bibcode:1997AJ....113..354F. doi:10.1086/118258.
- MacAlpine, Gordon M.; Ecklund, Tait C.; Lester, William R.; Vanderveer, Steven J.; Strolger, Louis-Gregory (2007). "A Spectroscopic Study of Nuclear Processing and the Production of Anomalously Strong Lines in the Crab Nebula". The Astronomical Journal. 133 (1): 81–88. arXiv:astro-ph/0609803 . Bibcode:2007AJ....133...81M. doi:10.1086/509504.
- Minkowski, Rudolph (September 1942). "The Crab Nebula". The Astrophysical Journal. 96: 199. Bibcode:1942ApJ....96..199M. doi:10.1086/144447.
- Bolton, John G.; Stanley, G. J.; Slee, O. B. (1949). "Positions of three discrete sources of Galactic radio frequency radiation". Nature. 164 (4159): 101–102. Bibcode:1949Natur.164..101B. doi:10.1038/164101b0.
- Bowyer, S.; Byram, E. T.; Chubb, T. A.; Friedman, H. (1964). "Lunar Occultation of X-ray Emission from the Crab Nebula". Science. 146 (3646): 912–917. Bibcode:1964Sci...146..912B. doi:10.1126/science.146.3646.912. PMID 17777056.
- Haymes, R. C.; Ellis, D. V.; Fishman, G. J.; Kurfess, J. D.; Tucker, W. H. (1968). "Observation of Gamma Radiation from the Crab Nebula". The Astrophysical Journal Letters. 151: L9. Bibcode:1968ApJ...151L...9H. doi:10.1086/180129.
- Del Puerto, C. (2005). "Pulsars In The Headlines". EAS Publications. 16: 115–119. Bibcode:2005EAS....16..115D. doi:10.1051/eas:2005070.
- Bejger, M.; Haensel, P. (2002). "Moments of inertia for neutron and strange stars: Limits derived for the Crab pulsar". Astronomy and Astrophysics. 396 (3): 917–921. arXiv:astro-ph/0209151 . Bibcode:2002A&A...396..917B. doi:10.1051/0004-6361:20021241.
- Harnden, F. R.; Seward, F. D. (1984). "Einstein observations of the Crab nebula pulsar". The Astrophysical Journal. 283: 279–285. Bibcode:1984ApJ...283..279H. doi:10.1086/162304.
- Hester, J. Jeff; Scowen, P. A.; Sankrit, R.; Michel, F. C.; et al. (1996). "The Extremely Dynamic Structure of the Inner Crab Nebula". Bulletin of the American Astronomical Society. 28 (2): 950. Bibcode:1996BAAS...28..950H.
- Davidson, K.; Fesen, R. A. (1985). "Recent developments concerning the Crab Nebula". Annual Review of Astronomy and Astrophysics. 23 (507): 119–146. Bibcode:1985ARA&A..23..119D. doi:10.1146/annurev.aa.23.090185.001003.
- Tominaga, N.; Blinnikov, S. I.; Nomoto, Ken'Ichi (2013). "Supernova explosions of super-asymptotic giant branch stars: multicolor light curves of electron-capture supernovae". The Astrophysical Journal Letters. 771 (1): L12. arXiv:1305.6813 . Bibcode:2013ApJ...771L..12T. doi:10.1088/2041-8205/771/1/L12.
- Frail, D. A.; Kassim, N. E.; Cornwell, T. J.; Goss, W. M. (1995). "Does the Crab Have a Shell?". The Astrophysical Journal Letters. 454 (2): L129–L132. arXiv:astro-ph/9509135 . Bibcode:1995ApJ...454L.129F. doi:10.1086/309794.
- Palmieri, T. M.; Seward, F. D.; Toor, A.; van Flandern, T. C. (1975). "Spatial distribution of X-rays in the Crab Nebula". The Astrophysical Journal. 202: 494–497. Bibcode:1975ApJ...202..494P. doi:10.1086/153998.
- Erickson, W. C. (1964). "The Radio-Wave Scattering Properties of the Solar Corona". The Astrophysical Journal. 139: 1290. Bibcode:1964ApJ...139.1290E. doi:10.1086/147865.
- Mori, K.; Tsunemi, H.; Katayama, H.; Burrows, D. N.; Garmire, G. P.; Metzger, A. E. (2004). "An X-Ray Measurement of Titan's Atmospheric Extent from Its Transit of the Crab Nebula". The Astrophysical Journal. 607 (2): 1065–1069. arXiv:astro-ph/0403283 . Bibcode:2004ApJ...607.1065M. doi:10.1086/383521.
- van den Bergh, Sidney (1970). "A Jetlike Structure Associated with the Crab Nebula". The Astrophysical Journal Letters. 160: L27. Bibcode:1970ApJ...160L..27V. doi:10.1086/180516.
- Image By NASA, ESA, J. Hester and A. Loll (Arizona State University) - HubbleSite: gallery, release., Public Domain, https://commons.wikimedia.org/w/index.php?curid=516106
The aardvark is a medium-sized mammal that lives in Africa. It is known for its burrowing and as an insectivore. Burrowing because he digs to create burrows in which to live and rear its young. An insectivore because he feeds on insects. It roams over most of the southern two-thirds of the African continent, avoiding areas that are mainly rocky.
The aardvark looks vaguely like a pig, but It has an arched back and is sparsely covered with coarse hairs. is pale yellowish-gray in color and often stained reddish-brown by soil. It's rear legs are longer than front legs. The front feet have four toes, while the rear feet have five toes. Each toe bears a large, robust nail which is somewhat flattened and shovel-like, and appears to be intermediate between a claw and a hoof.
An aardvark is a rather heavy and large animal. It typically weighs between 80 and 180 lbs. An aardvark's length is usually between 3.4 and 4.2 ft. And when its tail of up to 28 in is taken into account, it can reach lengths of 7 ft 3 in. At the shoulder, it is up to 2 ft tall.
The aardvark's coat is thin, and the animal's primary protection is its tough skin. Its hair is short on its head and tail; however its legs tend to have longer hair. The hair on the majority of its body is grouped in clusters of 3-4 hairs. Its tail is very thick at the base and gradually tapers.
When it digs, a lot of dirt can be flying around, so it's got heavy hair in its nostrils, to help protect it from all the debree flying around.
One of the most distinctive characteristics of the Tubulidentata is their teeth. The teeth have no enamel coating and are worn away and regrow continuously. The aardvark is also born with two conventional pointy teeth at the front of the jaw. When these fall out, they are not replaced. Adult aardvarks have only cheek teeth at the back of the jaw. These remaining teeth are peg-like and rootless and are of unique composition. The teeth consist of 14 upper and 12 lower jaw molars.
The aardvark's stomach has a muscular pyloric area that acts as a gizzard to grind swallowed food up, thereby rendering chewing unnecessary.
Habitat and range
Aardvarks are found in sub-Saharan Africa, where suitable habitat (savannas, grasslands, woodlands and bushland) and food (i.e., ants and termites) is available. They spend the daylight hours in dark underground burrows to avoid the heat of the day. The only major habitat that they are not present in is swamp forest, as the high water table precludes digging to a sufficient depth. They also avoid terrain rocky enough to cause problems with digging. They have been documented as high as 10,500 ft in Ethiopia. They are present throughout sub-Saharan Africa all the way to South Africa with few exceptions. These exceptions include the coastal areas of Namibia, Ivory Coast, and Ghana. They are not found in Madagascar.
Aside from digging out ants and termites, the aardvark also excavates burrows in which to live; of which they generally fall into three categories: burrows made while foraging, refuge and resting location, and permanent homes. Temporary sites are scattered around the home range and are used as refuges, while the main burrow is also used for breeding. Main burrows can be deep and extensive, have several entrances and can be as long as 43 ft. These burrows can be large enough for a man to enter. The aardvark changes the layout of its home burrow regularly, and periodically moves on and makes a new one. The old burrows are an important part of the African wildlife scene. As they are vacated, then they are inhabited by smaller animals like the African wild dog, ant-eating chat, Nycteris thebaica and warthogs. Other animals that use them are hares, mongooses, hyenas, owls, pythons, and lizards. Without these refuges many animals would die during wildfire season. Only mothers and young share burrows; however, the aardvark is known to live in small family groups or as a solitary creature.
Ecology and behavior
Aardvarks live for up to 23 years in captivity. Its keen hearing warns it of predators: lions, leopards, cheetahs, hunting dogs, hyenas, and pythons. Some humans also hunt aardvarks for meat. Aardvarks can dig fast or run in zigzag fashion to elude enemies, but if all else fails, they will strike with their claws, tail and shoulders, sometimes flipping onto their backs lying motionless except to lash out with all four feet. They are capable of causing substantial damage to unprotected areas of an attacker. They will also dig to escape as they can, when pressed, dig extremely quickly. Their thick skin also protects them to some extent.
The aardvark is nocturnal and is a solitary creature that feeds almost exclusively on ants and termites. They avoid eating the African driver ant and red ants. The only fruit eaten by aardvarks is the aardvark cucumber. In fact, the cucumber and the aardvark have a symbiotic relationship as they eat the subterranean fruit, then defecate the seeds near their burrows, which then grow rapidly due to the loose soil and fertile nature of the area. The time spent in the intestine of the aardvark helps the fertility of the seed, and the fruit provides needed moisture for the aardvark. This is one of many examples of interdependence in nature, which requires all systems in nature to exist at the same time.
Due to their stringent diet requirements, they require a large range to survive. An aardvark emerges from its burrow in the late afternoon or shortly after sunset, and forages over a considerable home range encompassing 10 to 30 kilometres (6.2 to 18.6 mi). While foraging for food, the aardvark will keep its nose to the ground and its ears pointed forward, which indicates that both smell and hearing are involved in the search for food. They zig-zag as they forage and will usually not repeat a route for 5–8 days as they appear to allow time for the termite nests to recover before feeding on it again.
During a foraging period, they will stop and dig a "V" shaped trench with their forefeet and then sniff it profusely as a means to explore their location. When a concentration of ants or termites is detected, the aardvark digs into it with its powerful front legs, keeping its long ears upright to listen for predators, and takes up an astonishing number of insects with its long, sticky tongue—as many as 50,000 in one night have been recorded. Its claws enable it to dig through the extremely hard crust of a termite or ant mound quickly. When successful, the aardvark's long (up to 12 in) tongue licks up the insects; the termites' biting, or the ants' stinging attacks are rendered futile by the tough skin. After an aardvark visit at a termite mound, other animals will visit to pick up all the leftovers. Termite mounds alone don't provide enough food for the aardvark, so they look for termites that are on the move. When these insects move, they can form columns 33–130 ft long and these tend to provide easy pickings with little effort exerted by the aardvark. These columns are more common in areas of livestock or other hoofed animals.
On a nightly basis they tend to be more active during the first portion of the night time (20:00-00:00); however, they don't seem to prefer bright or dark nights over the other. During adverse weather or if disturbed they will retreat to their burrow systems. They cover between 1 and 3 mi per night; however, some studies have shown that they may traverse as far as 19 mi in a night.
The aardvark is a rather quiet animal. However, it does make soft grunting sounds as it forages and loud grunts as it makes for its tunnel entrance. It makes a bleating sound if frightened. When it is threatened it will make for one of its burrows. If one is not close it will dig a new one rapidly. This new one will be short and require the aardvark to back out when the coast is clear.
The aardvark is known to be a good swimmer and has been witnessed successfully swimming in strong currents. It can dig a yard of tunnel in about five minutes, but otherwise moves fairly slowly.
When leaving the burrow at night, they pause at the entrance for about ten minutes, sniffing and listening. After this period of watchfulness, it will bound out and within seconds it will be 33 ft away. It will then pause, prick its ears, twisting its head to listen, then jump and move off to start foraging.
If attacked in the tunnel, it will escape by digging out of the tunnel thereby placing the fresh fill between it and its predator, or if it decides to fight it will roll onto its back, and attack with its claws. The aardvark has been known to sleep in a recently excavated ant nest, which also serves as protection from its predators.
Image by MontageMan
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Why fire ants are dangerous and what makes them so powerful?
A typical fire ant colony produces large mounds in open areas, and feeds mostly on young plants and seeds. Fire ants often attack small animals and can kill them. Unlike many other ants, which bite and then spray acid on the wound, fire ants bite only to get a grip and then sting (from the abdomen) and inject a toxic alkaloid venom called solenopsin, a compound from the class of piperidines. For humans, this is a painful sting, a sensation similar to what one feels when burned by fire (hence the name) and the after effects of the sting can be deadly to sensitive people. Fire ants are more aggressive than most native species and so have pushed many species away from their local habitat. One such species that Solenopsis ants parasitically take advantage of are bees, such as Euglossa imperialis, a non-social orchid bee species, from which the ants would enter the cells from below the nest and rob the cell's contents. These ants are renowned for their ability to survive extreme conditions. They do not hibernate, but can survive cold conditions, although this is costly to fire ant populations as observed during several winters in Tennessee, where 80 to 90% of colonies died due to several consecutive days of extremely low temperatures.
Although most fire ant species do not bother people and are not invasive, Solenopsis invicta, known in the United States as the red imported fire ant (or RIFA) is an invasive pest in many areas of the world, notably the United States, Australia, China and Taiwan. The RIFA was believed to have been accidentally introduced to these countries via shipping crates, particularly with Australia when they were first found in Brisbane in 2001. These ants have now since been spotted in Sydney for the first time. They were believed to be in the Philippines, but they are most likely to be misidentified for Solenopsis geminata ants.
In the US the FDA estimates that more than US$5 billion is spent annually on medical treatment, damage, and control in RIFA-infested areas. Furthermore, the ants cause approximately $750 million in damage annually to agricultural assets, including veterinarian bills and livestock loss, as well as crop loss. Over 40 million people live in RIFA-infested areas in the southeastern United States. About 60% of people living in fire ant-infested areas are stung each year. RIFA are currently found mainly in subtropical southeastern USA states including Florida, Georgia, South Carolina, Louisiana, Mississippi, Alabama, and parts of North Carolina, Virginia, Tennessee, Arkansas, Texas, Oklahoma, New Mexico, and California.
Since September 2004 Taiwan has been seriously affected by the red fire ant. The US, Taiwan and Australia all have ongoing national programs to control or eradicate the species, but, except for Australia, none have been especially effective. In Australia, there is an intensive program costing A$175 million, although the fire ant had remained despite efforts. By July 2013 multiple sites west of Brisbane were confirmed, including the Lockyer Valley, Muirlea and Goodna. According to a study published in 2009, it only took seventy years for the lizards in parts of the United States to adapt to the ant's presence – they now have longer legs and new behaviors that aid them in escaping from the danger.
Symptoms and treatment for fire ant sting
The venom of fire ants is composed of alkaloids derived from piperidine (see Solenopsis saevissima). Some people are allergic to the venom, and as with many allergies, may experience anaphylaxis, which requires emergency treatment. Management of an emergency visit due to anaphylaxis is recommended with the use of adrenaline. The sting swells into a bump, which can cause much pain and irritation, especially when several stings are in the same place. The bump often forms into a white pustule, which can become infected if scratched, but if left alone will usually flatten within a few days. The pustules are obtrusive and uncomfortable while active and, if they become infected, can cause scarring.
First aid for fire ant stings includes external treatments and oral medicines. There are also many home remedies of varying efficacy, including immediate application of urine or aloe vera gel, the latter of which is also often included in over-the-counter creams that also include medically tested and verified treatments. External, topical treatments include the anesthetic benzocaine, the antihistamine diphenhydramine, and the corticosteroid hydrocortisone. Antihistamines or topical corticosteroids may help reduce the itching and will generally benefit local sting reactions. Oral medicine include antihistamines. Severe allergic reactions to fire ant stings, including severe chest pain, nausea, severe sweating, loss of breath, serious swelling, and slurred speech, can be fatal if not treated.
Appearance of fire ants
The bodies of mature fire ants, like the bodies of all typical mature insects, are divided into three sections: the head, the thorax, and the abdomen, with three pairs of legs and a pair of antennae. Fire ants of those species invasive in the United States can be distinguished from other ants locally present by their copper brown head and body with a darker abdomen. The worker ants are blackish to reddish and their size varies from 2 to 6 mm (0.079 to 0.236 in). In an established nest these different sizes of ants all are present at the same time.
Solenopsis spp. ants can be identified by three body features—a pedicel with two nodes, an unarmed propodeum, and antennae with 10 segments plus a two-segmented club. Many ants bite, and formicine ants can cause irritation by spraying formic acid; myrmecine ants like fire ants have a dedicated venom-injecting sting, which injects an alkaloid venom, as well as mandibles for biting.
Fire ant queens, the reproductive females in their colony, are generally the largest. Their primary function is reproduction; fire ant queens may live up to 7 years and can produce up to 1,600 eggs per day, and colonies will have as many as 250,000 workers. The estimated potential life span is around 5.83 to 6.77 years. Young, virgin fire ant queens have wings (as do male fire ants), but they rip them off after mating.
Males mate with the queen. They die soon after mating.
There are other types of roles in an ant colony like the workers and the soldier ants. The soldier ants are known for their larger and more powerful mandibles while the worker takes care of regular tasks (the main tasks in a colony are caring for the eggs/larvae/pupae, cleaning the nest, and foraging for food). However, Solenopsis daguerrei colonies contain no workers, as they are considered social parasites.
NGC 7635: The Bubble Nebula ExpandingIt's the bubble versus the cloud. NGC 7635, the Bubble Nebula, is being pushed out by the stellar wind of massive star BD+602522, visible in blue toward the right, inside the nebula. Next door, though, lives a giant molecular cloud, visible to the far right in red. At this place in space, an irresistible force meets an immovable object in an interesting way. The cloud is able to contain the expansion of the bubble gas, but gets blasted by the hot radiation from the bubble's central star. The radiation heats up dense regions of the molecular cloud causing it to glow. The Bubble Nebula, pictured here is about 10 light-years across and part of a much larger complex of stars and shells. The Bubble Nebula can be seen with a small telescope towards the constellation of the Queen of Aethiopia (Cassiopeia).
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The M81 Galaxy Group through the Integrated Flux Nebula
Distant galaxies and nearby nebulas highlight this deep image of the M81 Group of galaxies. First and foremost in this 80-exposure mosaic is the grand design spiral galaxy M81, the largest galaxy in the image, visible on the lower right. M81 is gravitationally interacting with M82 just above it, a large galaxy with an unusual halo of filamentary red-glowing gas. Around the image many other galaxies from the M81 Group of galaxies can be seen, as well as many foreground Milky Way stars. This whole galaxy menagerie is seen through the glow of an Integrated Flux Nebula (IFN), a vast and complex screen of diffuse gas and dust also in our Milky Way Galaxy. Details of the red and yellow IFN, digitally enhanced, were imaged by a new wide-field camera recently installed at the Teide Observatory in the Canary Islands of Spain.
Image Credit: IAC
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