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Maurizio Paolillo » 11.Supernova remnants


Contents

  • Stellar remnants of Supernova explosions.
  • Supernovae Remnants:
    • Shell Supernova Remnants.
    • Plerions.
    • Mixed type SNR

Stellar Remnants of SNe

If the star is relatively low mass, roughly M<25M, it can be supported by neutron degeneracy and becomes a neutron star.

For more massive stars, the gravitational attraction overcomes neutron degeneracy, and the core collapses to form a black hole.

Internal structure of a Neutron star

Internal structure of a Neutron star

An artist view of the light from the Milky Way galaxy distorted by a Black Hole

An artist view of the light from the Milky Way galaxy distorted by a Black Hole


Supernova Remnants

Supernovae remnants (SNR) can take different forms and evolve with time:

  • Shell-type SNR (e.g. Cas A).
  • Plerions (e.g. Crab nebula).
  • Mixed type SNR.

SN1987A: the (young) remnant

The central ring is due to ejection by a stellar wind prior to the explosion.
Lies in the plane that contains the centre of explosion:

  • Glows due to [OIII] emission, excited by radiation from the explosion.
  • When the shock wave from the explosion reached this ring, in 2004, it excited the gas causing it to glow brightly.

The two other rings are not in the plane of the explosion, but in front of and behind the star. The explanation of these rings is still unknown.

Hubble image of SN1987A

Hubble image of SN1987A

An enlarged image of the central ring, due to gas excited by the SN shock.

An enlarged image of the central ring, due to gas excited by the SN shock.


Shell-type SNR

  • X-ray, radio, and optical emission come from a shell. X-rays are usually thermal, but can have non-thermal components.
  • Shell is expanding.
  • Power source is inertia left from initial supernova. No current input of energy.
RCW 86, this Supernova exploded in 185 AD

RCW 86, this Supernova exploded in 185 AD


Shell-type SNR: Cassiopeia A

X-ray image of the Cassiopeia A supernova remnant. Different colors represent X-ray emission at different wavelengths which are caused by emission lines of different elements

X-ray image of the Cassiopeia A supernova remnant. Different colors represent X-ray emission at different wavelengths which are caused by emission lines of different elements


Cassiopeia A

X-ray image of the Cassiopeia A supernova remnant. Different colors represent X-ray emission at different wavelengths which are caused by emission lines of different elements

X-ray image of the Cassiopeia A supernova remnant. Different colors represent X-ray emission at different wavelengths which are caused by emission lines of different elements


Old Supernava remnants

Very old (10,000s years) supernova remnants fade back into interstellar space enriching it with heavier elements

Very old (10,000s years) supernova remnants fade back into interstellar space enriching it with heavier elements


Supernova remnants

Cygnus loop: this is a ~15,000 year old remnant.

The filaments are caused by shocks encountering the interstellar medium. These shocks excite the gas which then emits emission lines.

A small part of the Cygnus loop supernova remnant, expanding from left to right. The Hubble image is courtesy of NASA

A small part of the Cygnus loop supernova remnant, expanding from left to right. The Hubble image is courtesy of NASA


Plerions

Center filled or Crab-like SNR, or pulsar wind nebulae:

  • X-ray, radio, and optical emission come from a filled, central region. X-rays are non-thermal.
  • Motions can be detected internal to the nebula.
  • Continuously powered by relativistic wind from pulsar at center of nebula.
The Crab nebula in X-rays as imaged by the Chandra Observatory. The Supernova exploded in 1054 AD

The Crab nebula in X-rays as imaged by the Chandra Observatory. The Supernova exploded in 1054 AD


Plerions: the Crab nebula

The Crab nebula is ~2 kpc away, with an angular size of 4×2 arcminutes.

The expansion velocity is measured from the Doppler shift to be 1450 km/s.

The source of the luminosity and electrons is a pulsar in the centre of the nebula.

Exercise: estimate the age of the nebula. How bright would the supernova that gave rise to the Crab nebula have been?

Crab nebula: believed to be the remnant of the supernova that went off in 1054 A.D.

Crab nebula: believed to be the remnant of the supernova that went off in 1054 A.D.


The Crab nebula

Combined optical (Hubble) and X-ray (Chandra) image of the Crab pulsar. Courtesy of NASA.

Combined optical (Hubble) and X-ray (Chandra) image of the Crab pulsar. Courtesy of NASA.


The Crab nebula

Composite image of the Crab nebula: X-rays (blue), optical (green), radio (red)

Composite image of the Crab nebula: X-rays (blue), optical (green), radio (red)


Mixed Morphology SNR

Plerionic composite: shell-type on the outside, Crab-like at the center.

  • Thermal composite: Radio shell, center-filled X-ray emission, but X-rays are thermal.
  • Thought to occur in denser ISM than shell-type SNR.
  • X-rays may be due to evaporation of clouds ISM after shock front has passed.
W28: red = radio, green = Hα, blue = X-ray,

W28: red = radio, green = Hα, blue = X-ray,


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