Located about 40 million light years away in the constellation of Dorado (The Dolphinfish), this galaxy is classified as a grand design spiral. It was discovered over 200 years ago by James Dunlop, a Scottish astronomer. The two prominent spiral arms are traced by bright blue star clusters and dark dust lanes. This image was colorized by Leo Shatz from three greyscale Hubble images. It appeared in the 2 July 2019 Astronomy Picture of the Day. What follows this image are three more examples all oriented the same to make easier visual comparisons.
Image Credit: NASA, ESA, Hubble; Processing & Copyright: Leo ShatzContinue reading →
On 8 May 2022, Astronomy Picture of the Day post this beautiful image from NASA/ESA/Hubble of spiral galaxy NGC 1512 in the far southern skies. The small bright blue central band is called a nuclear ring. Two distinct darker brown spiral arms are gas and dust falling inward from the larger ring at the edges of the image. This in-falling material results in much new star formation yielding the bright blue cast. There are also many areas of new star formation seen in blue scattered around the larger ring.
Browsing the Hubble Legacy Archive, the Great Barred Spiral got my attention. I downloaded three greyscale images filtered in blue, green, and red wavelengths which I combined into this color version with software. The result didn’t appear to me as a large spiral galaxy. Spiral arms were present around a bright core of stars. But, it seemed to be missing some larger dimensions than this image showed.
Hubble Legacy Archive | NGC 1365 | Color composite Jim RuebushContinue reading →
I enjoy making color composites from three grayscale images using the technique in this post. The colors assigned are not necessarily what the human eye would see, but are used to bring out details in structure and composition. Gallery of previous Astro-Images.
NGC 4845
This spiral galaxy is located in the constellation Virgo about 65 million light years away. Seen nearly edge-on, the bright core and the surrounding dust clouds are visible. The blue areas are artifacts of the original Hubble images used to make this composite.
Astronomers can observe the wavelengths of light from the galaxy to the left and right of the core. Rotation of the galaxy causes Doppler Shift of the wavelengths. The part of the galaxy moving away causes the wavelengths to be longer than normal. The part moving toward us causes the wavelengths to be shorter. The amount of shift in wavelengths indicates speed of rotation. A very massive central core of a galaxy results in fast rotation speeds.
Measurements of this galaxy allow astronomers to conclude a Black Hole resides in the core with a mass about 300,000 times the mass of our Sun. The galaxy was originally discovered by William Herschel in 1786.
Spiral galaxies are common in the universe. This nearly face-on example from the Hubble Telescope is found 111 million light-years away in the constellation Centaurus. Most of them swirl in a direction one might intuitively assume. This one appears to go in a counter-clockwise direction. Analysis using images by the Hubble Telescope show the outer arms moving clockwise instead. Evidence suggests it consumed a smaller companion galaxy which disturbed its rotation.
Drs. Ron Buta and Gene Byrd from the University of Alabama, Tuscaloosa, and Tarsh Freeman of Bevill State Community College in Alabama, observed NGC 4622 in ultraviolet, infrared, and blue and green filters. Their findings were presented to the American Astronomical Society in January 2002.
How I See It 