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NGC 7538 & IC 11 (Pacman Nebula)
Brynn Greenway & Gwyneth Findlay

NGC7538 IC11
NGC 7538 - Brynn Greenway IC 11 - Gwyneth Findlay

A nebula is a cloud of dust, hydrogen, and helium that is found between stars in space. This is also where stars are often formed. The four main types of nebulae are emission, absorption, reflection, and planetary. They are formed when there is a gravitational collapse and matter begins to stick together to become a more dense object. In the center of the collapsing matter, stars can potentially form (Williams).  

IC 11 is an emission nebula— a hot gas cloud energized by nearby ultraviolet light (Arnett)—that is between 80 and 100 light years across. Also known as NGC 281 or the "Pacman Nebula," IC 11 is about 10,000 light years from Earth in the Cassiopeia constellation (Wikipedia). Within the nebula is open cluster IC 1590, which contributes to the luminosity of the nebula (Nemiroff & Bonnell). Overall, the luminosity of the region is faint and best viewed using long exposures, but it is visible by amateur telescopes in dark sky regions on Earth (Wikipedia). The nebula is also home to dense dust globules which, if not first dispersed by stellar wind and radiation from the hot stars of the cluster, will one day be breeding grounds for new stars (Nemiroff Bonnell). The nebula has a number of dark regions, called Bok globules, which are not visible in this photo. Most Bok globules contain one or more protostars. IC 11 was discovered in 1883 by E.E. Barnard based on measurements first made in 1875. More recent measurements show little change in the nebula between the initial data and present day (Wikipedia).  

NGC 7538 is a high mass nebula that is very young and still taking mass away from a molecular cloud. It is located in a constellation called Cepheus, which is very close to a well-known nebula called Bubble Nebula. This particular nebula is located about 9, 100 light years from Earth (Wikipedia). It also contains the biggest protostar that has been discovered. Several large stars are currently forming in this nebula. It is an emission and reflection nebula (Voisey). Being an emission nebula means that it is a cloud of really hot gas. It is energized by UV light that comes from another star and emits radiation as its atoms move down energy levels. Because it is a reflection nebula, it is made of dust that reflects the light emitted by other stars in its area (Arnett). 

IC 11 and NGC 7538 are both emission nebulae where ultraviolet light reflects off hot gas and in which new stars are incubating (Arnett). Both nebulae are similar distances from Earth (Wikipedia). The nebulae are located fairly close to one another on the celestial sphere as the constellations Cepheus and Cassiopeia are neighbors. Both IC 11 and NGC 7538 contain some young, hot stars with a great enough luminosity to be visible from Earth by amateur telescope (Wikipedia). 

NGC 7538 contains darker colors at the violet end of the spectrum, with orange light visible in high-quality photographs (Voisey)Though darker in general color, NGC 7538 does not have the dark regions of Bok globules like IC 11. While NGC 7538 is home to the largest known protostar, IC 11 has Bok globules that are likely incubating protostars that we can't yet see (Wikipedia). NGC 7538 may once have had Bok globules that have since cleared to reveal protostars.

 

References:

Arnett, Bill. Types of Nebulae 10 Feb. 1997, astro.nineplanets.org/twn/types.html. Accessed 15 Nov. 2016.

Nemiroff, R., & Bonnell, J. "Portrait of NGC 281." NASA 25 Aug. 2011, http://apod.nasa.gov/apod/ap110825.htmlAccessed 1 Dec. 2016. 

"NGC 281." Wikipedia 18 June 2016, https://fr.wikipedia.org/wiki/NGC_281,  https://en.wikipedia.org/wiki/NGC_281. Accessed 1 Dec. 2016. 

"NGC 7538." Wikipedia 19 July 2016, https://en.wikipedia.org/wiki/NGC_7538. Accessed 15 Nov. 2016. 

Voisey, Jon. "A Peek Inside NGC 7538." Universe Today 24 Dec. 2015,  www.universetoday.com/81107/a-peak-inside-ngc-7538/. Accessed 15 Nov. 2016. 

 Williams, Matt. "Nebulae: What Are They and Where Did They Come From?." Universe Today 24 Dec. 2015, www.universetoday.com/61103/what-is-a-nebula/. Accessed 1 Dec.  2016. 

 

Object NGC 7538 IC 11
Right Ascension (J2000) 23:13:38 00:52:59
Declination (J2000) 61:30:41.997 +56:37:19
Filters used B (Blue), C (Clear), R (Red), V (Green) B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B (300s), V (150s), and R (150s); C (300s x 2) B (300s); V and R (150s); C (300s x 2)
Image dimension 516x403 pixels; 11.18x8.73 arcminutes 974x658 pixels; 21.1x14.26 arcminutes
Date/time observed October 17, 2016, 02:40:45'UT October 4, 2016, 09:36:47 UT

 

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