Galaxy NGC 253 (the Silver Coin)

Figure 1- NGC 253 as seen through binoculars (Screen-shot was taken from DSO Browser, 2017)

 

Galaxy NGC 253

Nestled within a group of galaxies situated around the south galactic pole, is a bright and energetic galaxy known as Galaxy NGC 253. From it first being discovered in the late 1700’s, many astronomical studies of the region have produced large amounts of detail and continued research. Being an easily observable galaxy with only a small amount of optical aid, it is ideal for both research and observing.


As with most objects in the night sky, Galaxy NGC 253 is also known by many other titles. The Silver Dollar Galaxy or the Silver Coin, are names given due to the appearance of the galaxy when observed through a small telescope (Nemiroff & Bonnell 2016; Wikimedia 2017). Equally, when observing NGC 253, it could be listed as ESO 474-29, C 65, MCG -4-3-9, PGC 2789, or UGCA 13 (DSO Browser 2017). However, due to its locality within its group of galaxies and thus its location within the boundary of a constellation called Sculptor, it more commonly referred as the Sculptor Galaxy (Nemiroff & Bonnell 2016; NOAO 2017). Likewise, these multiple names extend to this group of galaxies. Making up this unit, the galaxies are also identified as the Sculptor Group (NOAO 2017; Wikimedia 2017). Additionally, given that these groups are in close proximity to the south galactic pole and are encircling it, the Sculptor Group maybe then referred to as the South Polar Group (NOAO 2017; Non-Messier Indexes, 2009). Despite these labels, Galaxy NGC253 is not particularly difficult to find. During the southern hemisphere spring, particularly in mid-November, the constellation of Sculptor is at zenith around 9 pm Eastern Standard Time allowing the bright NGC 253 galaxy to be seen at its best (Wallace, Dawes & Northfield 2016. P.68-69). Once the location of Sculptor is established, the Sculptor Galaxy can be seen near the star Beta Ceti through a standard small telescope, or even binoculars (see Figure 1) (DSO Browser, 2017; Wikimedia 2017). Significantly, Sculptor Galaxy is a very bright galaxy making it easily observed. As the brightest galaxy and the biggest in its group, only the likes of Andromeda are brighter and therefore, NGC253 is referred to as one the brightest galaxy outside of our local group (Non-Messier Indexes, 2009; Nemiroff & Bonnell 2016). Notably, Sculptor Galaxy is ~7.1 magnitude in visual brightness, thus making it reasonably bright to see through ocular aids (Non-Messier Indexes, 2009). With a visual aid of your choosing, look towards the south galactic pole for a bright object noted as NGC 253.

Since Galaxy, NGC 253 was discovered and due to its localised position, it has been widely studied. In September 1783, Caroline Herschel first discovered it during her searches for comets (Nemiroff & Bonnell 2016; Wikimedia 2017). Since then, various astronomers have studied the dust lanes and spiral patterns, including strong star-forming regions, star clusters and star deaths (Nemiroff & Bonnell 2016; Wikimedia 2017). Due to this frantic birth and death within NGC 253, it is considered to be a Starburst Galaxy (NOAO 2017). Due to the high rate of star formation, many super star clusters develop containing stars known as Wolf-Rayet stars and emit strong stellar winds (Gábor Tóth Astrophotography 2016). Further, these strong winds influence the galaxy. The rate of this galactic wind is a limiting factor in star formation, the stellar makeup and blow out into the galaxy halo, joining with the shockwaves of supernova and produce columns of dark perpendicular outflows (Gábor Tóth Astrophotography 2016; Bolatto et al 2013). This stellar wind has an outflow rate ~9 solar masses per year, measured from the H alfa emission and from tracking these winds to speeds of hundreds of km/s (Bolatto et al 2013). Significantly, these winds carry particles that may just linger in the halo, eventually raining back down onto galaxy disk and form a recycling procedure of the galaxy (Bolatto et al 2013). More generally, information that has been studied since the galaxies discovery has been researched and provides a good understanding of NGC 253. The galaxy classification (De Vaucouleurs system) has been determined to be SAB(s)c, meaning it is an intermediate galaxy (Gábor Tóth Astrophotography 2016). It has a declination ~25degress, at ~10 million lights year away and spanning 70 thousand light-years across (Non-Messier Indexes, 2009; Nemiroff & Bonnell 2016; DSO Browser, 2017). Strong readings have been detected in high-energy x-rays and gamma rays, leading to the presence of a supermassive black hole ~5 million solar masses (Nemiroff & Bonnell 2016; Wikimedia 2017). And a small redshift has been detected of 0.0008 (DSO Browser, 2017). Overall, continued research in many different areas has been undertaken and continues to be completed, building a greater knowledge in NGC 253.

As one of the closest galaxies outside of our local group, the Sculptor Galaxy NGC 253 is a very bright and energetic galaxy. Astronomers have continued copious research, due largely to its localised location and for the continued understanding of Starburst Galaxy internal interactions. Continued studies into the galaxy and the significance of stellar winds, star formation, dust lanes, galactic halo and all its interactions, a better understanding of NGC 253 will develop and ultimately knowledge of our own Milky Way Galaxy. As astronomers’ study, observers can gaze at its grandeur towards the south and amongst the group surrounding the south galactic pole.

 

References:

o   Bolatto, AD, Warren, SR, Leroy AK, Walter, F, Veilleux, S, Ostriker, EC, Ott, J, Zwaan, M, Fisher, DB, Weiss, A, Rosolowsky, E, Hodge, J, 2013, ‘The Starburst-Driven Molecular Wind in NGC 253 and the Suppression of Star Formation’, ESO, July 2013,viewed 30 October 2017, <https://www.eso.org/public/archives/releases/sciencepapers/eso1334/eso1334a.pdf>

o   DSO Browser, 2017, Sculptor Galaxy, viewed 30 October 2017, <https://dso-browser.com/deep-sky/1137/sculptor-galaxy/ngc-253/galaxy>

o   Gábor Tóth Astrophotography 2016, The Silver Dollar Galaxy - NGC 253, viewed 31 October 2017, <http://astro.i-net.hu/node/136>

o   NOAO – see National Optical Astronomy Observatory

o   Non-Messier Indexes, 2009, NGC 253, viewed 30 October 2017, <http://www.messier.seds.org/xtra/ngc/n0253.html>

o   National Optical Astronomy Observatory, 2017, The Sculptor Galaxy, NGC253, viewed 24 October 2017, <https://www.noao.edu/image_gallery/html/im1017.html>

o   Nemiroff, R & Bonnell, J 2016, ‘NGC 253: Dusty Island Universe’, Astronomy Picture of the Day, viewed 23 October 2017, <https://apod.nasa.gov/apod/ap161103.html>

o   Wallace K, Dawes G & Northfield P 2016, Astronomy 2017 Australia, Your guide to the night sky, Quasar Publishing, NSW, Australia

Wikimedia Foundation Incorporated, 2017, Sculptor Galaxy, viewed 23 October 2017, <https://en.wikipedia.org/wiki/Sculptor_Galaxy> 

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