Daily Image
01-05-2007
Whirlpool Galaxy
| Submitter: | Albert van Duin |
| Description: | The Whirlpool Galaxy (M51 or NGC 5194) was discovered by Charles Messier on October 13, 1773. Its companion galaxy, NGC 5195, was discovered in 1781 by Pierre Méchain. It was not until 1845 that the Whirlpool Galaxy became the first to be recognized as a spiral. This was achieved by Lord Rosse using a 72 inch reflecting telescope he had constructed at Birr Castle, Ireland. With the recent supernova 2005cs derived estimate of 23 Million light years distance, and an angular diameter of roughly 11.2 arcminutes, we can infer that M51's bright circular disk has a diameter of about ~38,000 light-years. Its mass is estimated to be 160 billion solar masses. Compared to 100 kly diameter of the Milky Way, M51 has about half its size and mass. The very pronounced spiral structure of the Whirlpool Galaxy is believed to be the result of the close interaction between it and its companion galaxy NGC 5195. Induced spiral structure in the larger galaxy isn't the only effect of the interaction. Significant compression of hydrogen gas occurs that leads to the development of starbirth regions. In pictures of M51 these show up as the bright blue 'knots' throughout the spiral arms. Decades ago, it wasn't known for certain if the companion galaxy NGC 5195 was actually a true companion or rather some other galaxy passing at a distance. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated the reality of the interaction. Recent simulations bear out that M51's spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 comes from behind M51 through the disk towards the observer, made another disk crossing as recently as 50 to 100 Myrs ago until it is where we observe it to be now, slightly behind M51. Source: http://en.wikipedia.org/wiki/Messier_51 This image is a 115 minute integration made with an ASA 8 inch Astrograph and Canon 350D DSLR from Beilen on April 7, 2007. Some more images can be found at http://www.astropix.nl |
| Copyright: | Albert van Duin |
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