October 2015 - Galaxy of the Month
NGC 7541 in Pisces
The galaxy pair NGC 7541 and NGC 7537 in Pisces were both discovered by William Herschel in 1785, although NGC 7541 may also be the nebulous object which was seen by Horace Tuttle in 1875 whilst looking for Encke’s comet and later catalogued as NGC 7581. They are both located within the circlet of Pisces.
NGC 7541 and NGC 7537 are probably a true galaxy pair, although this is not 100% certain. They are both spiral galaxies at a distance of around 33 Mpc. NGC 7537 is classed as Sbc and NGC 7541 as SBc i..e. a barred spiral. Both galaxies are see close to edge on. At this distance NGC 7537 would be about 94000 light years across and NGC 7541 about 145000, so comparable in size to our Milky Way galaxy.
NGC 7541 was home to the type Ia supernova 1998dh. Not to be outdone NGC 7537 was home to supernova SN 2002gd. This would appear to have been a Type II-p.
It would appear from X-Ray observations that NGC 7541 is currently undergoing a period of high star formation. Whether this is in anyway related to a gravitational interaction with NGC 7537 is questionable.
In 1999 astronomers combined images from two different camera on the Hubble space telescope to try and estimate the ages of the stars in the central regions of NGC 7537. This study appears to suggest that the bulges of spiral galaxies formed in a relatively short time in the early universe. This may have happened by the collapse of a single large gas cloud or by the merger of large star clusters.
Both these two galaxies appear in NSOG Vol 1 and would appear to be visible in telescopes in the 20-22cm category, although instruments with a larger aperture will be required to see much detail. Both galaxies are also described in Luginbuhl and Skiff’s Observing Handbook and Catalogue of Deep Sky objects as reasonable in 25cm but easier with 30cm. NGC 7537 is fainter of the two and may require a larger aperture to be sure of.
Owen Brazell - Galaxy Section Director