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 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.

Astro-Images | The Meathook

In the far southern skies is the constellation Piscis Volans, the flying fish. Within Volans lies this galaxy NGC 2442. It is distorted from the more common spiral shape into a meathook appearance. The unusual shape is likely the result of a close encounter with another galaxy not in the field of view. The galaxy lies about 50 million light years away. Visible are darkened dust lanes, young blueish star clusters, and reddish star forming regions. More views are from Astronomy Picture of the Day here, here, and here.

European Southern Observatory

I tried my hand at producing a color version of the Meathook galaxy using 3 greyscale images from the Hubble Telescope. The process is described in this previous post. The Hubble images provide rich detail.

Hubble Legacy Archive | NGC 2442 | My version

Astro-Images | Centaurus-A

Centaurus-A is located in the southern hemisphere skies.  I have never seen it from my location 42˚ north latitude. It rises only 5˚ above my southern horizon in early December. I’m certain it is very familiar to my blogger friend Roger in Australia.  It is the 5th brightest galaxy and easily viewed by amateurs. It contains a black hole of 55 million solar masses ejecting jets of x-ray and radio wavelengths. Models suggest the galaxy collided with another smaller galaxy in the past leading to areas of star formation in the resulting complex structure. I enjoyed combining 3 greyscale Hubble images into this composite. In the center are several newly formed bluish stars. The dark areas are dust blocking the passage of light.

Centaurus-A | Hubble Legacy Archive | My Version


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Astro-Images | Doing Cartwheels

Like many people these days, I have a lot of spare time. One project I enjoy is taking three grey-scale images from the Hubble Telescope archive and combining them to produce color versions. The Hubble Legacy Archive (HLA) collects the vast array of images from the telescope into a searchable site available to the public. Knowing the name of the object or keywords, one can search for images made by a variety of instruments and filters.

The oval object below is an unusual galaxy called the Cartwheel. It was imaged with a grey-scale sensor as the light passed through a green wavelength filter. Imaging was also done with red and blue wavelength filters not show here. But, they look similar.

Hubble Legacy Archive

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