Supernova in the Pinwheel Galaxy

By Anthony Ayiomamitis | Perseus.gr

Supernovae represent the violent explosions of massive stars which have reached the end of their life-cycle. The one indicated by the black tick marks above was photographed Aug. 26 from Athens. It was discovered Aug. 24. This reverse monochrome image shows the supernova in the familiar Pinwheel Galaxy, a.k.a. Messier 101 or NGC 5457.

A supernova is a massive explosion where the bulk of a star’s material is ejected into space and the interstellar medium are characterized with luminosities which easily can exceed that of the host galaxy for a brief period of a few weeks or even months. This ejection of material including heavy elements is both vital and critical for new generations of stars and exoplanets.

Supernovae are classified into one of two primary types. White dwarfs which gain matter via accretion have their cores collapse once they approach the Chandrasekhar limit of 1.38 solar masses, thus yielding a Type Ia supernova. Accredition of matter can be accomplished by a variety of means including via a close binary star companion or a merger with another white dwarf. In contrast, type Ib and Ic involve large stars which have exhausted their available fuel and collapse due to gravity. Type II supernovae involve much more massive stars (at least nine solar masses) where the nuclear fusion follows a steady path from lighter to progressively heavier elements (such as hydrogen to helium which is then converted to carbon etc) and until nuclear fusion is no longer possible at the core due to the iron and nickel that has been accumulated, thus leading to a huge core collapse and an ensuing stellar explosion.

Spectroscopy has also played a key role in identifying the type of supernova one observes and, in fact, now forms the basis for their classification. More specifically, type Ia supernovae are characterized without any hydrogen emission lines in their spectra and in contrast to type II which exhibit strong hydrogen emission lines. Furthermore, type I are further subdivided on the basis of the presence of a silicon line (615nm, type Ia), a helium line (type Ib) or neither one (type Ic) in their spectra.

Many supernovae leave behind them spectacular gas clouds and stellar remnants (neutrinos) which cover multiple Full Moons in width across the sky. Regrettably, for residents of the Northern Hemisphere, only four supernova remnants (SNR) are visible and, more specifically, the Crab Nebula (M1) in Taurus, the massive Veil complex (NGC 6960, 6974, 6979, 6992, 6995) in Cygnus, the Jellyfish Nebula (IC 433) in Gemini and Simeis 147 (aka Shajn 147, Sh 2-240) also in Taurus. The most recognized supernova remnant is perhaps the Crab nebula in Taurus which is believed to have exploded in 1054 AD as documented by Chinese astronomers of the time whereas Simeis 147 is especially dim and represents one of the faintest objects in the sky.

Note: Using differential photometry (AIP4Win V2.4.0) with GSC 3852:1108 (mag 11.7) and GSC 3852:1069 (mag 11.9) as comparison and check stars, respectively, the mean magnitude for SN2011fe (PTF11kly) is mag 13.290+0.003.