Supernova Remnant (snr)

Diffuse, Expanding Nebula That Results From A Supernova Explosion. A Snr Consists Of Material Ejected In The Supernova Explosion And Interstellar Material Swept Up By The Passage Of The Shock Wave From The Exploded Star. Snrs Tend To Be Powerful X-ray And Radio Emitters Due To Interactions With The Surrounding Ism. They Typically Last Several Hundred Thousand Years Before Dispersing Into The Ism.

during Supernova Explosion, A Shock Wave Is Sent Out Through The Star, Passing Through The Stellar Material And Into The Surrounding Ism Creating A Shock Wave In The Interstellar Gas In The Forward Direction, And A Shock In The Reverse Direction, Back Into The Supernova Ejecta. The Shocked Material Is Heated To 106s K Resulting In The Emission Of Thermal X-rays. The Shock Wave Also Pushes The Ism Into An Expanding Shell Which Emits Huge Amounts Of Synchrotron Radiation. The Supernova Ejecta Expands Freely Into The Surrounding Volume Of Relatively Low Density With Typical Velocities Of ~10,000 Km/s. This free Expansion Phase Lasts 100–200 Years Until The Mass Of The Ism Swept Up By The Shock Wave Exceeds The Mass Of The Ejected Material.

image Source: http://astronomy.swin.edu.au/cms/astro/cosmos/s/supernova+remnant.

when Free Expansion Stops And Rayleigh-taylor Instabilities Arise. These Instabilities Mix The Shocked Ism With The Supernova Ejecta And Enhance The Magnetic Field Inside The Snr Shell. This adiabatic (sedov-taylor) Phase Lasts 10,000–20,000 Years. The Shock Wave Continues To Cool, And Once Temperatures Drop Below About 20,000 K, Electrons Start Recombining To Form Heavier Elements And Radiating Energy. During This radiative Phase, The Recombination Process Radiates Energy Much More Efficiently Than By Thermal X-rays And Synchrotron Emission And The Shock Wave Cools And Ultimately Disperses Into The Surrounding Ism.

snr Are Categorized Into Three Main Types Based On Their Appearance, With The Differences Arising Due To Variations In Initial Progenitor And Explosion Conditions, Density Variations In The Interstellar Medium (ism) And Rayleigh-taylor Instabilities. shell-type Remnants Emit Most Of Their Radiation From A Shell Of Shocked Material. This Appears As A Bright Ring, Due To Limb Brightening. crab-type Remnants
the Crab Nebula – are powered by a pulsar located at their center. In contrast to shell-type remnants, this type emits most of its radiation from within the expanding shell. Consequently, they appear as a filled region of emission rather than a ring of emission. Composite remnants are a cross between the other two remnant types, and appear either shell-like or Crab-like, depending on the wavelength of the observations. In general, thermal composites appear shell-like at radio wavelengths and Crab-like in X-rays, while plerionic composites appear Crab-like at both radio and X-ray wavelengths, but also show shell structures.


Modified from images source: http://astronomy.swin.edu.au/cms/astro/cosmos/S/Supernova+Remnant+Type.

Supernova remnants disperse the heavy elements made in supernova explosions into the ISM. Additionally, they provide much of the energy to heat the ISM and are probably responsible for the acceleration of galactic cosmic rays.