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Object of the week 26 February 2017: NGC 3115, The Spindle Galaxy
Object of the week 26 February 2017: NGC 3115, The Spindle Galaxy
NGC 3115 (Other designations: UGCA 199, PGC 29265, Caldwell 53)
Type: Edge-On Lenticular Galaxy
Classification: S0
Constellation: Sextans
RA: 10h 05m 14.0s
Dec: −7° 43′ 07″
Magnitude: 9.8v,
Mean Surface Brightness: 12.1
Size: 7.2’ x 2.6’
Hiding deep in the apparent emptiness of the constellation Sextans, far away from both the galaxy madness of Virgo and Leo, and from the great galactic nebulae of the winter, is a real deep sky gem: The lenticular galaxy NGC 3115, also known as the “Spindle Galaxy”.
NGC 3115 is an S0 galaxy, seen close to edge-on from our perspective. With an estimated distance of 30 million light years away, the Spindle is smaller than the Milky Way, having a diameter of about 40,000 light years. Recent research with the Hubble Space Telescope has provided strong evidence of a massive black hole larking in the center of the (very bright) nucleus. In 2011, using the Chandra X-Ray observatory, a flow of hot gas in the black hole has been imaged, and haw confirmed the earlier speculations that NGC 3115’s central black hole has a mass of about two billion suns, making it the closest ultra-massive black hole to our galaxy.
Attachment 2484
NGC 3115 as imaged at Chile, http://www.astrosurf.com/antilhue/ngc3115.htm
The Spindle Galaxy is quite bright, at magnitude 8.9, and has a high surface magnitude of 12.1. These data, along with its dimensions of 7x3 arc-minutes, and a declination of 7 degrees south, point out to a galaxy that ought to be well known, widely observed, and a star-party showstopper. Yet, few amateurs ever tackle it, possibly because it lies in a star-poor area and also because it is in the “shadow” of the Leo-Virgo galaxies.
My own single observation of this galaxy until 2017 was made back in 2004, with my Takahashi FS102 refractor, and my simple notes read “bright, small, longish ellipse”. I more or less forgot about its existence, until last January, when I came across a comment by the late Walter Scott Houston, saying that “it shows well in 5-inch binoculars. Looks similar in a 12-inch instrument…”, so I decided to check it again.
I first observed the Spindle with my 120mm f5 achromatic refractor on the evening of January 31st, 2017. I noted a bright, rhomboid-shaped galaxy, with a very bright nucleus (actually, this bright nucleus can “hide” its form when observed under very low powers, it needs attention to note it’s not a star!). I could readily see from where the “spindle” name comes! The brightness profile of the galaxy was such that under dark skies should readily be visible even in the old style 60mm refractors.
Attachment 2485
NGC 3115 with my SkyWatcher 120mm f5 refractor
On the next evening I tried to observe NGC 3115 with my 18” dob, but while transparency was exceptional, the seeing was terrible. All I could make out was a spindle –shaped bright nebulous mass with a very bright core and long, but faint, extensions on the long axis.
Fast forward to March 3rd, 2017: Transparency was not the greatest, but finally I got steady seeing that allowed me to easily push magnification to 594X. And wow! What a grand sight NGC 3115 is in the big scope under good conditions! The main body of the galaxy is a bright 4:1 spindle – shaped patch of steady light, with its south side appearing slightly brighter and more linear. An intensely “burning” core punctuates the center of this bright mass, while long, but faint extensions emanate from both sides if the long axis. But the most surprising observation for me was what appeared to be some bright patches on both sides of the central bright core. They were small but not star-like, appearing just as smaller versions of the core. I did some other observations, and returned to the galaxy one hour later, and the observations were identical.
Attachment 2486
NGC 3115 with the 18" Obsession. Note that the magnification was 594X and not 297X as mentioned on the drawing (I forgot I used the 2X Barlows!).
I searched through the web for decent images of NGC 3115, to see if I could correlate the bright patches I saw around the core with similar patches in photograph, but to no avail. The central area of this galaxy is so bright that it almost always appears way over-exposed in photos, hiding the small details. I also searched all the books in my library for photos / drawings of NGC 3115, and finally found a drawing by Stephen J. O’ Meara (in his book “The Caldwell Objects”), which sort of corresponds with my observations. Apparently, under excellent, steady conditions, these details can come out in scopes as small as the 4” refractor O’Meara was using. I can’t wait for the next new moon window to re-observe the Spindle Galaxy with my refractors and see if I can duplicate my 18” (or O’Meara’s 4”!) observations!
So, next time you are out under beautiful spring skies, turn your scope to the emptiness of Sextans, locate the beautiful Spindle Galaxy, and...
GIVE IT A GO AND LET US KNOW!!
