David Grennan, an amateur from Dublin, has thrilled astronomers with his discoveries of supernovae in distant galaxies. Here is the inside story of his admirable achievements.
Astronomy is one of the few sciences where talented amateurs can make important contributions. As example you have only to look at the recent discovery of a supernova by Irish astronomer David Grennan. Grennan, an award-winning amateur observer, has already found a couple of asteroids but in terms of sheer magnitude his latest find surpasses his earlier achievements. He observed it on 17 September 2010 but it has just been independently confirmed by the team led by QUB’s Stephen Smartt.
A supernova is the titanic detonation of a star. Such cataclysms are the largest explosions known to occur in the Universe. A star undergoing a supernova can be radiating at any moment as much energy as all the other hundreds of billions of stars in its galaxy and can blaze away for months. Every century a couple of supernovae ought to occur in our own galaxy, the Milky Way, but are usually obscured by the great lanes of dust which thread their way through the spiral arms. The last confirmed supernova in the Milky Way to be observed was in 1604 (known to history as Kepler‘s Star; it was bright enough to be seen in the daytime sky). Ever since then all supernovae examined by astronomers have been denizens of other galaxies. Grennan’s supernova lies in a galaxy estimated to be 290 million light years (89 Mpc) away. This means that light of this vast cosmic explosion was blasted forth in the time before Pangaea split into the continents we know today, when dragonflies as big as seagulls ruled Earth’s skies.
Supernovae are categorised by their elements in their spectra and precisely how they brighten to a peak and decline. Type II supernova are easiest to describe, occurring when a vast star dies, with its core collapsing in upon itself to form a neutron star or even a black hole. A Type Ia supernova is believed to be caused by a white dwarf star in a compact binary system accumulating matter from its companion star until the density threshold for nuclear fusion occurs, resulting a titanic nuclear explosion. Types Ib and c would seen better considered as a subtype of Type II as their mechanisms are identical. Again they are believed to be triggered by the cores of huge stars imploding just like Type II but in their cases the the star has previous lost its outer layers either to a nearby companion star or through ferocious stellar winds making them deficient in hydrogen.
Grennan’s discovery appears to be a Type I b or c (they can be difficult to distinguish) but it demonstrates anomalies which make it especially scientifically intriguing. Making such an important discovery is a magnificent achievement and it is good to see David Grennan receiving the credit his skill deserves.
Grennan has discovered a second supernova, a Type 1c designated 2012ej, on 22 August 2012. It is in the the galaxy IC2611 in the constellation Lynx.