A galaxy refers to a huge system of stars, planets, gas, and dust that are gravitationally bound together. Our solar system, for instance, is part of the Milky Way galaxy, which is though to contain more than 100 billion other stars, and according to curent estimates the universe in its entirety is thought to contain upwards of two trillion different galaxies.
Most galaxies fall into well defined classifications, and are either spiral-shaped like the Milky Way, elliptical, or irregular shaped. However, there are some galaxies that defy all attempts at classification. While some strange and bizarre galaxies are the result of gravitational interactions with other more massive, and sometimes less massive objects, they all have one thing in common; they look more like artists’ impressions than real, tangible collections of billions of stars.
Take a look at the stunning photos below credited to the NASA image gallery, are they straight out of science fiction, or are they galactic marvels? You decide.
The Black Eye Galaxy (M64)
Type: Spiral Galaxy
Constellation: Coma Berenices
If it is possible for a galaxy to take on an evil aspect, M64 does it perfectly. Although colorful galaxies are plentiful, this one is strongly reminiscent of the garish pulp science-fiction magazine covers of the 1950’s. The red color is derived from hydrogen, which means that new stars are being formed in very large numbers, but what is really strange is that the objects consists of two contra-rotating systems. The inner part of the system rotates in one way, while the stars and dust in the outer parts to a distance of about 40,000 light years rotate in the other direction. At a distance of 17 million light years from earth, it is of course difficult to tell, but it seems likely that the contra-rotation of the two systems is the result of a recent (1 billion years or so) merger between two galaxies.
The Southern Pinwheel (M83)
Type: Barred Spiral Galaxy
There are many beautiful galaxies in the Universe, but this one, also known as M83, is among the most beautiful, even if beauty is only in the eye of the beholder. However, what makes this galaxy peculiar is the large number of supernova explosions that took place in it. Currently, there are eight active supernovas under observation, but the remains of hundreds more have been noted. The reasons for the large number of supernovas remain unexplained, but what is explainable is the huge number of active star forming regions, which are shown in pink. The pink color is the result of the enormous amount of UV light generated by millions of young, new stars that acts on surrounding clouds of dust and gas.
Sombrero Galaxy (M104)
Type: Unbarred Spiral Galaxy
It is fair to say that the central bulge, or nucleus, of a galaxy consists of one, homogeneous collection of stars. However, in the case of the Sombrero Galaxy, the nucleus is composed of several, clearly separate clusters of stars, although this is not readily apparent in optical light. Astronomers are also at a loss to explain the presence of the dust lane that encircles the core, but what is more puzzling is the intricate detail in the dust lane. Investigations into the origin and nature of the dust lane are ongoing, but a clear answer seems to be a long way off.
Centaurus A (NGC 5128)
Type: Elliptical Galaxy
Convention dictates that a large galaxy can only be a spiral, or an elliptical, but not both, which is what makes Centaurus A the strange beast it is. In optical light, Centaurus A is a huge elliptical galaxy, but the really strange thing is that in higher frequencies, a deeply buried spiral becomes apparent. Current thinking is that the spiral component is the remains of a spiral galaxy that was absorbed by the larger, and more massive elliptical, but it is highly unlikely that the interaction would have left the spiral intact, or even recognizable. The image above clearly shows the preserved spiral structure, but only because the image was taken in several X-ray frequencies, and then further enhanced.
Type: Elliptical Galaxy
If the Southern Pinwheel Galaxy is what active galaxies should look like, then NGC 474 is how they should not look. This is not an artist’s impression from the cover of a science-fiction novel, but a real galaxy that is being torn apart by the tidal influences of the spiral galaxy behind, and above it. However, it is because of the tenuous shells of gas and dust that gives this galaxy the appearance of a jelly fish, that we know that many, if not most known galaxies have similar gas shells around them as the direct result of collisions or near-misses with other galaxies in the (cosmologically speaking) recent past.
Arp 87 (NGC 3808A/NGC 3808B)
Type: Interacting Galaxies
While collisions between galaxies are relatively common, near misses are not. The interaction between these two galaxies, NGC 3808A and NGC 3808B, has been going on for several billion years, and chances are that they will keep on swinging around each other until they eventually merge into one gigantic irregularly shaped galaxy. For the moment however, they remain tethered by a tenuous leash of stars, gas, and dust.
Antennae Galaxies (NGC 4038/NGC 4039)
Type: Interacting Galaxies
This is another example of a merger on a galactic scale, and the only way to tell that there were two galaxies involved is by the presence of the two large luminous yellow blobs that used to be the cores of the respective galaxies. Many, if not most of the existing globular clusters in the two merging galaxies will not survive the merge process. The constantly varying tidal effects will rip them apart, and chances are only the very biggest clusters will survive, and then almost certainly not in their present form. This is the clearest example of what will happen about 4 billion years from now when the Milky Way and Andromeda galaxies meet head on.
The Porpoise Galaxy (Arp 142)
Type: Interacting Galaxies
This galaxy is physics become art. Even though it resembles a dolphin, it is in fact a galactic merger, with the “eye” of the dolphin being the core of a large spiral galaxy that is being distorted by the tidal influence of an even larger galaxy below it. The area to the left of the “eye” that looks like the nose of the dolphin, is in fact a huge star forming region, in which young, hot new stars illuminate the surrounding gas and dust clouds. It is expected that in about a billion or so years, the dolphin shape will have transformed itself into a regular galaxy as the merger runs its course.
Type: Polar-ring Galaxy
Out of the millions of galaxies that have had their pictures taken, we know of only about a dozen or so galaxies of this type. The ring that encircles the galaxy, almost perpendicularly to the plane of the galactic disc, likely consists of the remains of a less massive galaxy that was pulled apart by the heavy weight, although investigations to either confirm, or eliminate this possibility are ongoing. Current investigations are focused on the behavior of the polar ring to see if dark matter or energy is in any way involved in the formation of similar rings around other galaxies of this type.
Hoag’s Object (PGC 54559)
Type: Ring Galaxy
When organized science was asked to explain the formation of something as bizarre as this galaxy, the answer was a collective, and resounding “Huh?” Not that we blame anyone, since there are only a few of these ring galaxies known. This one, however, is accompanied by another, smaller version in the background, which is as bizarre as the galaxies themselves.