Crab nebula

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Crab nebula
Crab Nebula.jpg
M1, the Crab nebula
Observation data: J2000.0 epoch
Type Supernova remnant
Right ascension 05h 34m 31.97s[1]
Declination +22° 00′ 52.1″[1]
Distance 6.5 ± 1.6 kly (2.0 ± 0.5 kpc)[2]
Apparent magnitude (V) +8.4
Apparent dimensions (V) 420″ × 290″[3][a]
Constellation Taurus
Physical characteristics
Radius 5.5 ly (1.7 pc) [4]
Absolute magnitude (V) −3.1 ± 0.5[b]
Notable features Optical pulsar
Other designations Messier 1,[1] NGC 1952,[1] Sharpless 244

See also: Diffuse nebula, Lists of nebulae

The Crab nebula [5] is a supernova remnant and 'pulsar wind nebula' in the constellation of Taurus. The nebula was observed by John Bevis in 1731; it corresponds to a bright supernova recorded by Chinese and Islamic astronomers in 1054.

The nebula is about 6,500 light-years (2 kpc) from Earth. It has a diameter of 11 ly (3.4 pc) and expands at a rate of about 1,500 kilometers per second. It is part of the Perseus Arm of the Milky Way Galaxy.

At the center of the nebula lies the Crab pulsar, a neutron star (or spinning ball of neutrons), 28–30 km across,[6] which emits pulses of radiation from gamma ray bursts to radio waves with a spin rate of 30.2 times per second. The nebula was the first astronomical object identified with a historical supernova explosion.[7]

The nebula acts as a source of radiation for studying celestial bodies between it and us. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab'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 cloudy remnants of SN 1054 are now known as the Crab Nebula. The nebula is also referred to as Messier 1 or M1, being the first Messier object catalogued in 1758.

Energy levels[change | change source]

Previous analysis showed that with X-ray and gamma ray energies above 30 keV, the Crab is the strongest persistent source in the sky. Its flux (energy emission) was known to be above 1012 eV.

However, recent work has shown the energy levels are much higher than previously thought.[8] Scientists found emissions at more than 100 GeV (gigaelectronvolts) – 100 billion times more energetic than visible light.

Origins[change | change source]

The creation of the Crab Nebula corresponds to the bright SN 1054 supernova that was recorded by Chinese astronomers in 1054 AD. The Crab Nebula itself was first observed 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. The Earl of Rosse observed the nebula at Birr Castle in 1848, and referred to the object as the Crab Nebula because a drawing he made of it looked like a crab.[9][10]

The Crab Nebula video by NASA

In the early 20th 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.[7][11] 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.[12] 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.[7]

References[change | change source]

  1. 1.0 1.1 1.2 1.3 "SIMBAD Astronomical Database". Results for NGC 1952. http://simbad.u-strasbg.fr/Simbad. Retrieved 2006-12-25.
  2. Kaplan, D.L. et al. (2008). "A precise proper motion for the Crab Pulsar, and the difficulty of testing spin-kick alignment for young neutron stars". Astrophysical Journal 677 (2): 1201. doi:10.1086/529026.
  3. Trimble, Virginia Louise (1973). "The distance to the Crab Nebula and NP 0532". Publications of the Astronomical Society of the Pacific 85 (507): 579. doi:10.1086/129507.
  4. Carroll, Bradley W.; Ostlie, Dale A.. "An introduction to modern astrophysics. 2nd ed". http://wps.aw.com/aw_carroll_ostlie_astro_2e/48/12319/3153834.cw/index.html.
  5. catalogue designations M1, NGC 1952, Taurus A
  6. "Crab Nebula: the spirit of Halloween lives on as a dead star creates celestial havoc". http://chandra.harvard.edu/photo/2006/crab/.
  7. 7.0 7.1 7.2 Mayall N.U. (1939). "The Crab Nebula, a probable supernova". Astronomical Society of the Pacific Leaflets 3: 145.
  8. BBC Science News 7 October 2011 Crab Pulsar's high-energy beam surprises astronomers [1]
  9. Glyn Jones, K. (1976). "The search for the nebulae". Journal of the History of Astronomy 7: 67.
  10. Rossi, B.B.. "The Crab Nebula ancient history and recent discoveries". NASA. NTRS. http://ntrs.nasa.gov/search.jsp?R=19700008151. Retrieved October 1, 1969.
  11. Lundmark, K. (1921). "Suspected new stars recorded in old chronicles and among recent Meridian observations". Publications of the Astronomical Society of the Pacific 33: 225. doi:10.1086/123101.
  12. 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. doi:10.1086/316401.