NGC 634, a perfect spiral galaxy

 
NGC 634, a perfect spiral galaxy

NGC 634 (also known as UGC 1164) is a nearly edge-on spiral galaxy about 120,000 light years across, located some 250 million light-years away in the Triangulum constellation.

The fine detail and exceptionally perfect spiral structure of the galaxy make it hard to believe that this is a real observation and not an artist’s impression.

The disk of the galaxy is ribboned with dark dust lanes, huge clouds of complex organic molecules expelled by stars being born and stars dying. A striking feature is the asymmetry of the lanes: they are darker on the bottom than at the top. Astronomers have no good explanation for this asymmetry yet.

In 2008 this galaxy became a prime target for observations thanks to the violent demise of a white dwarf star. The type Ia supernova known as SN2008a was spotted in NGC 634 and briefly rivalled the brilliance of its entire host galaxy but, despite the energy of the explosion, it can no longer be seen this image, which was taken around a year and a half later.

White dwarfs are thought to be the endpoint of evolution for stars between 0.07 to 8 solar masses, which equates to 97% of the stars in the Milky Way. However, there are exceptions to the rule; in a binary system it is possible for a white dwarf to accrete material from the companion star and gradually put on weight. Eventually the star can grow too full –when it exceeds 1.38 solar masses – and nuclear reactions will ignite, that produce enormous amounts of energy, and the star explodes as a type Ia supernova.

Other, far more distant galaxies can be seen in the background as well as right through the galaxy in this Hubble image.

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