Image: ESA/Hubble and NASA/V. Antoniou.
Among the many things that make NGC 2336 an astonishing galaxy are its eight sprawling spiral arms, a dramatic contrast to the four spiral arms of our Milky Way Galaxy, or the two arms of the Whirlpool Galaxy. Those eight arms are a haven for star formation, with 78 known large star-forming nebulae, including some that are comparable in size to another multi-limbed cosmic wonder, the giant Tarantula Nebula in the nearby Large Magellanic Cloud. The rate of star formation in NGC 2336 is about ten times higher than in our Galaxy.
NGC 2336 is also a huge galaxy, visibly spanning 200,000 light years across, embedded in a disc of hydrogen gas that radio-wavelength observations show extends even further. Contrast that with our Milky Way Galaxy, which is about 100,000 light years across. Inside NGC 2336’s bulge is a bar, 40,000 light years long, at the centre of which lurks a quiescent 30-million-solar-mass supermassive black hole. Often galaxies start forming stars in a multitude of nebulae after experiencing a gravitational close encounter with another galaxy. This is not the case with NGC 2336. Although there is another galaxy, IC 467, that is relatively close to it, the two are not gravitationally interacting. We can tell this from how undisturbed NGC 2336’s spiral arms are, and how quiet the central black hole is. With all that star formation, there is, correspondingly, star death. The year 1987 is famous for the supernova in the Large Magellanic Cloud (see News update, page 20), but it was also the year of the only known supernova – SN 1987L – in NGC 2336, which exploded that August. NGC 2336 has one other claim to fame: it’s the closest bright galaxy in the sky to Polaris, the Pole Star, but the proximity is illusory: NGC 2336 lies 100 million light years away in the constellation of Camelopardalis, the Giraffe.