Supernova remnant

Multiwavelength composite image of the remnant of Kepler's supernova, SN 1604.
Multiwavelength composite image of the remnant of Tycho's supernova, SN 1572.
Multiwavelength composite image of the supernova remnant N49 in the Large Magellanic Cloud.

A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.

There are two possible routes to a supernova: either a massive star may run out of fuel, ceasing to generate fusion energy in its core, and collapsing inward under the force of its own gravity to form a neutron star or a black hole; or a white dwarf star may accumulate (accrete) material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.

In either case, the resulting supernova explosion expels much or all of the stellar material with velocities as much as 10% the speed of light, that is, about 30,000 km/s. These ejecta are highly supersonic: assuming a typical temperature of the interstellar medium of 10,000 K, the Mach number can initially be > 1000. Therefore, a strong shock wave forms ahead of the ejecta, that heats the upstream plasma up to temperatures well above millions of K. The shock continuously slows down over time as it sweeps up the ambient medium, but it can expand over hundreds of thousands of years and over tens of parsecs before its speed falls below the local sound speed.

One of the best observed young supernova remnants was formed by SN 1987A, a supernova in the Large Magellanic Cloud that was observed in February 1987. Other well-known supernova remnants include the Crab Nebula, Tycho, the remnant of SN 1572, named after Tycho Brahe who recorded the brightness of its original explosion, and Kepler, the remnant of SN 1604, named after Johannes Kepler. The youngest known remnant in our galaxy is G1.9+0.3, discovered in the galactic center[1].


Summary of stages

An SNR passes through the following stages as it expands:

  1. Free expansion of the ejecta, until they sweep up their own weight in circumstellar or interstellar medium. This can last tens to a few hundred years depending on the density of the surrounding gas.
  2. Sweeping up of a shell of shocked circumstellar and interstellar gas. This begins the Sedov-Taylor phase, which can be well modeled by a self-similar analytic solution. Strong X-ray emission traces the strong shock waves and hot shocked gas.
  3. Cooling of the shell, to form a thin (< 1 pc), dense (1-100 million atoms per cubic metre) shell surrounding the hot (few million kelvin) interior. This is the pressure-driven snowplow phase. The shell can be clearly seen in optical emission from recombining ionized hydrogen and ionized oxygen atoms.
  4. Cooling of the interior. The dense shell continues to expand from its own momentum. This stage is best seen in the radio emission from neutral hydrogen atoms.
  5. Merging with the surrounding interstellar medium. When the supernova remnant slows to the speed of the random velocities in the surrounding medium, after roughly a trillion seconds, it will merge into the general turbulent flow, contributing its remaining kinetic energy to the turbulence.

Types of supernova remnant

There are three types of supernova remnant:

  • Shell-like, such as Cassiopeia A
  • Composite, in which a shell contains a central pulsar wind nebula, such as G11.2-0.3 or G21.5-0.9.
  • Mixed-morphology (also called "thermal composite") remnants, in which central thermal X-ray emission is seen, enclosed by a radio shell. The thermal X-rays are primarily from swept-up interstellar material, rather than supernova ejecta. Examples of this class include the SNRs W28 and W44. (Confusingly, W44 additionally contains a pulsar and pulsar wind nebula; so it is simultaneously both a "classic" composite and a thermal composite.)

Origin of cosmic rays

The remnant of SN 1006 observed in X-rays. The inner emission comes from the hot plasma, whereas the two bright caps are produced by electrons accelerated at the shock front.

Supernova remnants are considered the major source of galactic cosmic rays.[2][3][4] The connection between cosmic rays and supernovas was first suggested by Walter Baade and Fritz Zwicky in 1934. Vitaly Ginzburg and Sergei Syrovatskii in 1964 remarked that if the efficiency of cosmic ray acceleration in supernova remnants is about 10 percent, the cosmic ray losses of the Milky Way are compensated. This hypothesis is supported by a specific mechanism called "shock wave acceleration" based on Enrico Fermi's ideas, which is still under development.[citation needed]

Indeed, Enrico Fermi proposed in 1949 a model for the acceleration of cosmic rays through particle collisions with magnetic clouds in the interstellar medium.[5] This process, known as the "Second Order Fermi Mechanism", increases particle energy during head-on collisions, resulting in a steady gain in energy. A later model to produce Fermi Acceleration was generated by a powerful shock front moving through space. Particles that repeatedly cross the front of the shock can gain significant increases in energy. This became known as the "First Order Fermi Mechanism".[6]

Supernova remnants can provide the energetic shock fronts required to generate ultra-high energy cosmic rays. Observation of the SN 1006 remnant in the X-ray has shown synchrotron emission consistent with it being a source of cosmic rays.[2] However, for energies higher than about 1015 eV a different mechanism is required as supernova remnants cannot provide sufficient energy.[6]

See also


  1. ^ Discovery of most recent supernova in our galaxy May 14, 2008
  2. ^ a b K. Koyama, R. Petre, E.V. Gotthelf, U. Hwang, M. Matsuura, M. Ozaki, S. S. Holt (1995). "Evidence for shock acceleration of high-energy electrons in the supernova remnant SN1006". Nature 378 (6554): 255–258. Bibcode 1995Natur.378..255K. doi:10.1038/378255a0. 
  3. ^ "Supernova produces cosmic rays". BBC News. November 4, 2004. Retrieved 2006-11-28. 
  4. ^ "SNR and Cosmic Ray Acceleration". NASA Goddard Space Flight Center. Retrieved 2007-02-08. 
  5. ^ E. Fermi (1949). "On the Origin of the Cosmic Radiation". Physical Review 75 (8): 1169–1174. Bibcode 1949PhRv...75.1169F. doi:10.1103/PhysRev.75.1169. 
  6. ^ a b "Ultra-High Energy Cosmic Rays". University of Utah. Retrieved 2006-08-10. 

External links

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Supernova remnant G1.9+0.3 — is the youngest known supernova remnant (SNR) in the Milky Way Galaxy. [cite web| title = G1.9+0.3: Discovery of Most Recent Supernova in Our Galaxy. | | publisher = NASA | author = | date = 2008.05.14 | url =… …   Wikipedia

  • supernova remnant — noun A nebula that is formed from supernova explosion debris. The Crab Nebula is the most studied supernova remnant. Syn: SNR See Also: nova remnant …   Wiktionary

  • supernova remnant — Astron. an expanding shell of gas, with accompanying strong radio and x ray emissions, produced by a supernova. * * * …   Universalium

  • supernova remnant — Astron. an expanding shell of gas, with accompanying strong radio and x ray emissions, produced by a supernova …   Useful english dictionary

  • Vela Supernova Remnant — Diffuse nebula caption= A Skyfactory Visible Light image of Vela Supernova Remnant. Credit: Digitized Sky Survey/ESA/ESO/NASA FITS Liberator. name = Vela Supernova Remnant type = Supernova Remnant epoch = J2000.0 ra = 08h 35m 20.66s dec = 45° 10m …   Wikipedia

  • Supernova (disambiguation) — Supernova or Super Nova may mean:cience and astronomy* Supernova, an astronomical event, a type of stellar explosionAssociated with this type of event are: * Type Ia supernova * Type Ib and Ic supernovae * Type II supernova * Supernova remnant *… …   Wikipedia

  • Supernova nucleosynthesis — is the production of new chemical elements inside supernovae. It occurs primarily due to explosive nucleosynthesis during explosive oxygen burning and silicon burning.[1] Those fusion reactions create the elements silicon, sulfur, chlorine, argon …   Wikipedia

  • Supernova — This article is about the astronomical event. For other uses, see Supernova (disambiguation). Multiwavelength X ray, infrared, and optical compilation image of Kepler s supernova remnant, SN 1604. A supernova is a stellar explosion that is more… …   Wikipedia

  • Supernova-Überrest — Ein Supernovaüberrest (engl. supernova remnant, kurz SNR) ist ein Emissionsnebel, der durch eine Supernova entsteht und häufig eine Schalenstruktur aufweist. Die bei einer Supernova freiwerdende Energie wird zu 99 % als Neutrino Strahlung… …   Deutsch Wikipedia

  • supernova — /sooh peuhr noh veuh/, n., pl. supernovas, supernovae / vee/. Astron. 1. the explosion of a star, possibly caused by gravitational collapse, during which the star s luminosity increases by as much as 20 magnitudes and most of the star s mass is… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.