Supernovae constitute the violent death of stars, and their random occurrences have grabbed our attention for millennia, even when we had no explanation as to the origins of these bright “guest stars”. These events release high-energy radiation and cosmic rays, which if close enough to Earth, could destroy our ozone layer and inevitably life itself.
Some supernovae are formed by the implosion of a massive star that fuses iron in its core (Type II or “core collapse” supernovae), while others are a more special variety from white dwarf stars—stellar remnants formed by the same process responsible for creating planetary nebulae. Most white dwarf stars quietly cool off over billions of years, but this is not the case for all. Some may receive additional mass from a companion star. Due to the balance of gravity directed inward and electron degeneracy pressure (at the quantum level) directed outward, a white dwarf will collapse and explode as a different kind of supernova should its mass exceed 1.4 solar masses, an upper mass limit known as the Chandrasekhar limit. Because these specific supernovae consistently consume the same amount of mass, each will always have the same peak luminosity. This is important for cosmologists because white dwarf (Type Ia) supernovae can be used as “standard candles” for measuring distances.
In recent years, hundreds of supernovae have been discovered each year in other galaxies. However, not a single recorded one has originated from our own galaxy since 1604. With an expected Milky Way supernova rate of one every 100 years or so, it is fair to say that we have been overdue for another for quite some time!
- SN 2012aw in M95, in Leo
- SN 2012cj in NGC 4424, in Virgo *
- SN 2012fr in NGC 1365, in Fornax *
- SN 2014G in NGC 3448, in Ursa Major
- SN 2014J in M82 (Cigar Galaxy), in Ursa Major *
* Type Ia supernovae