Image Credit: André van der Hoeven, ESA/Hubble & NASA
Spiral Galaxy NGC 5806
NGC 5806 is a barred spiral galaxy of roughly 65,000 light-years across, located about 80 million light-years away from Earth in the constellation of Virgo (the Virgin) while it is receding from us at approximately 1359 kilometers per second.
It is home to an active galaxy nucleus – a very luminous, compact region at the center of the galaxy where a supermassive black hole is pulling in large amounts of matter from its immediate surroundings. As the matter spirals around the black hole, it heats up and emits powerful radiation.
The galaxy has a so-called disk-type bulge – the densest part in the center of the spiral arms – in which the spiral structure extends all the way to the center of the galaxy (instead of a large elliptical bulge of stars like many other galaxies have).
Two supernovae have been observed in this galaxy: on July 19, 2004 a Type II supernova called SN 2004dg (the afterglow from this outburst of light can be seen as a faint yellowish dot near the bottom of the galaxy) and on January 22, 2012 the Type IIb supernova SN 2012P.
A supernova is a phenomenon in which a star explodes in the final phase of its life. There are two types: Type I and Type II. The Type I are explosions of white dwarf stars and don’t show hydrogen in the spectra. The other group, Type II, are explosions of massive stars (at least 8 times, and no more than 40–50 times the mass of the Sun). The Type II supernovae do show hydrogen in their spectra.
A Type IIb supernova has only a weak hydrogen line in its initial spectrum, and later on the hydrogen emission becomes undetectable. The progenitor could have been a giant star which lost most of its hydrogen envelope due to interactions with a companion in a binary system, leaving behind the core that consisted almost entirely of helium.
However, the exploding star can become billions of times as bright as the Sun before gradually fading from view. At its maximum brightness, the exploded star may outshine an entire galaxy. Supernova explosions are enriching the intergalactic gas with elements like oxygen, iron, and silicon that will be incorporated into new generations of stars and planets.