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Spiral Galaxy (NGC 628) & (NGC 7331)
Jared Swanson & Sharon Suh

NGC628 NGC7331
Messier 74 - Jared Swanson Caldwell 30- Sharon Suh

NGC 628 or Messier 74 and NGC 7331 or Caldwell 30 are both spiral galaxies. A spiral galaxy, like our very own Milky Way, looks like a flat disk with a bulging center. Around the disk are spiral arms, making it look like a sleeping jellyfish. All of the stars, planets, and gas within the galaxy are found in the the disk, which rotates around the bulge at speeds of hundreds of kilometers per second. This intense speed is what causes the galaxy to take its specific shape. Some take interesting shapes, such as the sombrero galaxies. Older stars can be found in the bulge while in the spiral arms there is an ongoing star formation.

Messier 74 (NGC 628) is located in the constellation Pisces and is nicknamed the Phantom galaxy. In 1780, it was discovered by French astronomer, Pierre Mechain. Mechain then told of his discovery to Charles Messier who added it to his catalog. The diameter of this galaxy is 95,000 ly across and about 30 million light-years away from us. There is a whopping 100 billion stars, which is still less than our Milky Way, which has about 300 billion stars. As you can faintly see in the picture above, there are blue and pink dots throughout the spiral arms, which branch out from the central bulge. The blue dots are young stars and the pink dots are regions of ionized hydrogen. These regions emit a large amount of ultraviolet light. Also in these spiral arms are cosmic dust lanes and this is similar to our own galaxy, the Milky Way.

Caldwell 30 (NGC 7331) was found by English astronomer, William Herschel in 1784. It is the brightest galaxy in the Pegasus constellation and there are several background glaxies visible when looking at Caldwell 30. This galaxy is 100,000 light-years across and about 49 million light years away from the Earth. It is also getting farther from the earth at an amazing speed of 816 kilometers per second. Light from old, cool stars are found in central bulge while the spiral arms contain many stars along with dark dust lanes. In the very center there is a supermassive black hole that is about 4.1 million solar masses! A interesting feature of the galaxy is that the inner stellar disk is moving in retrograde motion relative to the rest of the galaxy.

The discovery of the galaxies occured in the same decade; Pierra Mechain found Messier 74 in 1780 and William Herschel found Caldwell 30 in 1784. Both Caldwell 30 and Messier 74 are spiral galaxies and because of this the concentration of young stars is in the spiral arms. Also in these spiral arms, both galaxies contain cosmic dust lanes. These galaxies have about the same diameter, where Messier 74 is about 95,000 light-years across and Caldwell 30 is only 5,000 light-years larger. In their respective galaxies, Messier and Caldwell are the dominant galaxies in there constellation.

Messier 74's recessional velocity is 657 kilometers per second away from earth and Caldwell 30 is moving much faster at 816 kilometers per second. Caldwell's distance from earth is much greater than that of Messier 74 by almost 20 million light-years.

References:

Chander, R. and J. Miller. "Holiday Wishes from the Hubble Space Telescope." HubbleSite. <http://hubblesite.org/newscenter/archive/releases/2007/41/image/a/>

Normandin, George. "Spiral Galaxy NGC 7331, Galaxy Group." Kopernik. <http://www.kopernik.org/images/archive/n7331.htm>

Wikipedia, "Messier 74".

Wikipedia, "NGC 7331".

Object Messier 74 Caldwell 30
Right Ascension (J2000) 1:36:42 22:37:04.1
Declination (J2000) 15:46:60 34:24:56
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 (240s), and R (200s); C (240s) B (300s), V (240s), and R (200s); C (240s)
Image dimension 1092x736 pixels; 23.8x16.1 arcminutes 1092x736 pixels; 23.8x16.1 arcminutes
Date/time observed November 15, 2015, 12:05 UT November 15, 2015, 12:05 UT

 

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