Supernova Remnants (SNR's)

[M SNR] Click to go to the only supernova remnant in Messier's catalog, the first object, the Crab Nebula M1. M1 is also shown in the icon.
When a star explodes in a supernova explosion, it depends on its type what exactly remains. But anyway, the offbursted gaseous remainders will form a rapidly expanding and slowly fading cloud, mixing with the interstellar matter which is "swept up" when the shell expands, and is a domain of an extreme kind of physics. These nebulae are called supernova remnants (SNRs). Depending on the type of the supernova, there may also be a central compact remnant in the form of a neutron star.

According to current theory, two different mechanisms produce supernovae: First, stars considerably more massive than our Sun can most probably not evolve quietly into an end state as a white dwarf. When coming to age, these massive stars explode in a most violent detonation which flashes up at a luminosity of up to 10 billion times that of the sun, called supernova (of type II, or Ib or Ic), and ejecting the very greatest part of the stellar matter in a violently expanding shell. These explosions are thought to leave a compact remnant, such as a neutron star. Aternatively, infalling matter on a white dwarf star can cause it to explode as a supernova of type Ia; these events do probably not leave a stellar remnant.

The classification of supernovae in types was introduced by Rudolph Minkowski (Minkowski 1941) on the grounds of their spectra: Type I supernovae show no hydrogen lines in their spectra, whereas these lines are present in those of Type II. Later these types were subdivided, again based on their spectra. For Type I, subtype Ia shows no Helium in spectrum, characteristic absorption features, and in its later phase, emission lines from elements in the iron group. Type Ib shows helium lines, type Ic no helium but in its later phase, oxygen and calcium lines. Supernovae of types Ib and Ic are thought to originate from massive progenitor stars which have been stripped off their outer layers by companion stars, and thus lost their hydrogen and for Ic, also their helium.

The Crab Nebula M1 is the only Messier SNR, the remnant of the supernova of 1054 (very probably of Type II), one of few historical supernovae observed in our Milky Way galaxy. However, other supernovae have appeared in Messier galaxies (see our table), and produced SNRs. These special kind of nebulae can be observed in some cases, e.g. the remnant of the Supernova 1993J in M81.

The knowledge of the nature of the supernova phenomenon, and the name "supernova", goes back to Walter Baade and Fritz Zwicky, who studied Novae in the early 1930s at Mt. Wilson Observatory. They were especially interested, and successful, in finding extremely bright "novae" in other galaxies, comparable to the one which had been observed in the Andromeda Galaxy M31 in 1885 (S Andromedae). They coined the term "Super-Novae" in 1934 (Baade, Zwicky 1934).

Interesting resources on supernova remnants: Supernova resources: References:
Diffuse Nebulae

Planetary Nebulae

Dark Nebulae

Hartmut Frommert
Christine Kronberg
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Last Modification: September 3, 2005