Astro-Image | NGC 4845

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.

Astro-Image | Backward Galaxy NGC 4622

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.

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Astro Images | Ring Nebulae

Browsing the Hubble Legacy Archive, I was intrigued by a small ring shaped nebula NGC 6369. It is also known as the Little Ghost. Discovered by 18th century astronomer Sir William Herschel, it lies over 2000 lt-yrs away in the constellation Ophiucus. The sun-like star at the center explosively blasted away its outer layers creating the ring of glowing gases. The star radiates strongly in ultraviolet causing the glow of the nebula. The blast also reduced the star to a white dwarf. For this color image, I combined three blue, green, and red filtered grey-scale Hubble images. The colors illustrate the presence of ionized oxygen, hydrogen, and nitrogen atoms.

NGC6369 | Hubble Legacy Archive | My Version

Fellow amateur astronomer Roger captured an image of his own recently of a different ring-shaped nebula NGC 7293 in his southern hemisphere sky. It is published here in his blog Cosmic Focus.

Astronomy fans are likely familiar with Messier 57 high in the summer sky of the northern hemisphere. It is another fine example of a ring nebula. Follow the link for a beautiful image and description.

Astro Images | Two Galaxy Views

There are billions of billions of galaxies in the known universe. They are oriented in countless different ways. A small fraction show their full face toward Earth, while some show an edge-on view. This first example is a nearly face-on view of NGC 4414. Imaged by the Hubble Telescope in 1995, it lies about 60 million lt-yr from Earth. Only about half of the galaxy fit into the detector of Hubble due to its large size.

Three red, green, and blue filtered greyscale images were used to make my color version of this galaxy. The center region is densely populated with older yellow and red stars. This is typical of spiral galaxies. The outer regions are less populated and include younger blue stars. The galaxy has a lot of dust mixed into the spiral arms as evidenced by the dark clouds and bands in silhouette against the bright star glow.

This next galaxy is a nearly perfect edge-on view of NGC 4013. The very bright light source at the heart of this galaxy is actually a star in the foreground much closer than the galaxy. It is part of our Milky Way galaxy and just happens to be in alignment. NGC 4013 is about 55 million lt-yr away in the direction of Ursa Major, the Big Dipper. If we could see it face-on, it would have a spiral shape similar to NGC 4414 above. What stands out clearly in this edge-on view is the dark band of dust cutting across the width of the galaxy. A few blue stars show in the upper right. They are in an outer band and less obscured by the dust.