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 Dayhere, here, and here.
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.
Spiral galaxies are common in the universe. This example of the Pinwheel Galaxy M101 from the Hubble Telescope is found in Ursa Major, the Big Dipper.
About ⅔ of the spiral galaxies also have a feature in the center called a bar. This next example, also from Hubble, is known as NGC 1300. Some bars are very long and pronounced, as this one. Other galaxies have a bar that is quite short.
Notice in each galaxy the blue cast in the spiral arms. It comes from the glow of relatively young stars. Older stars tend to glow white, yellow, or orange. The vein-like structures are regions darkened by the absorption of dust.
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.
Albert Einstein published his General Theory of Relativity in 1916. One aspect of the theory predicted that light passing near a massive object would be deflected slightly in direction. Light originating from a distant bright source such as a quasar could travel by a massive object such as a galactic center and change direction. The observer would see the image of the distant source in slightly different places.
Not to scale.
Of course, such a prediction deserved to be tested. In 1919, astronomer Arthur Stanley Eddington headed a team to observe a star closely aligned with the Sun that would be visible only during a total eclipse. The star’s known position should be shifted according to the theory. Their observations confirmed that Einstein was correct.
What is an Arp? Good question. Arp is the last name of Halton Arp. He compiled the Atlas of Peculiar Galaxies containing 338 entries published in 1966 by the California Institute of Technology. A goal was to show images of the peculiar structures found among some galaxies.
Among the billions of galaxies known, a few are in some stage of collision with another. Such a rare event disrupts the original shapes of the colliding galaxies. Collisions take a long time to occur. This image of atlas entry number 220 shows the result of two galaxies in collision. The brown dust lanes hide much of the detail behind the dust. It is a chaotic scene.