Image Credit: Fred Calvert, Adam Block, KPNO, AURA, NSF (via Cold Springs Observatory)
This pretty galaxy could easily be confused with the
Triangulum galaxy, but the two, in fact, are not related. Instead, this is
NGC 2403: a remarkable spiral galaxy seen face-on from our vantage point. It can be found approximately 8 to 12 million light-years from Earth in the Camelopardalis constellation.
Like Triangulum, NGC 2403 has spans around 50,000 light-years across — making both just half the size of the Milky Way — and uncountable number of pinkish H II regions. In fact, i can't think of a single galaxy lit up by more of them than this one, which is most likely the product of a galaxy merger of some kind.
Up-Close and personal look at NGC 2403 (Image Credit: Subaru Telescope (NAOJ), Hubble Legacy Archive; Processing: Robert Gendler)
Also seen in this stunning image, near the 9 o'clock position (beneath the galaxy's central core), is a supernova that happens to be one of the brightest in recent memory, called
SN2004dj. Other members of the Messier 81
(M81) galaxy group, which contains over 34 galaxies, linger nearby — namely NGC 2404. It's so close, the two are literally connected by the arm.
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Japanese amateur astronomer Koichi Itagaki discovered the supernova on July 31, 2004, with a small telescope. Additional observations soon showed that it is a "Type II supernova," resulting from the explosion of a massive, hydrogen-rich star at the end of its life. The cataclysm probably occurred when the evolved star's central core, consisting of iron, suddenly collapsed to form an extremely dense object called a neutron star. The surrounding layers of gas bounced off the neutron star and also gained energy from the flood of ghostly "neutrinos" (tiny, almost non-interacting particles) that may have been released, thereby violently expelling these layers.
This explosion is ejecting heavy chemical elements, generated by nuclear reactions inside the star, into the cosmos. Like other Type II supernovae, this exploding star is providing the raw material for future generations of stars and planets. Elements on Earth such as oxygen, calcium, iron, and gold came long ago from exploding stars such as this one.
Astronomers will continue to study SN 2004dj over the next few years, as it slowly fades from view, in order to gain a better understanding of how certain types of stars explode and what kinds of chemical elements they eject into space.
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