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The Endless Waltz

If there was a time signature for this waltz it would be written in 3,000,000,000/4 or something along those lines.  That’s 3 billion beats per measure and a quarter note is one beat for my musically un-inclined friends.  Ninety million light years away in the pair of galaxies called Arp 271 a long, slow dance has begun between two similar spiral galaxies, NGC 5426 and NGC 5427.  Both are spiral galaxies located in the constellation Virgo.  The two galaxies began interacting likely a several million years ago and the evidence of their intertwining is now readily visible in this beautiful image from the Mt. Lemon Sky Center in Arizona.  The gravity between the interacting galaxies has begun to pull some of the outer stars towards the center creating a bridge of stars.  The bright pink colored gas inside the galaxies are massive molecular clouds which have been energized by the extra gravitation pull and have begun igniting new stars and will cause others to explode in supernovae.

Little is currently known about the fate of these two waltzing galaxies yet.  It all depends on how fast they’re travelling through the cosmos.  At a higher speed they’ll smash right into each other and rip themselves apart.  Once scattered about, gravity will eventually pull the remains back together again.  Or, if they’re not travelling all that fast they’ll kind of do-si-do around each other, until they ultimately merge into one massive new galaxy.  Either way the dance will take millions and millions of years to complete.  The study of colliding galaxies is an intriguing topic because it gives us insight as to what will happen in a couple billion years when our own galaxy will collide with our nearest neighbor, the Andromeda galaxy.

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

A Hybrid Galaxy

What happens when a massive elliptical galaxy and a spiral galaxy meet?  In the case of the galaxy Centaurus A, the spiral galaxy gets ripped apart!  The stunning new image of Centaurus A, also known as NGC 5128, reveals more about the nature of interacting galaxies and how supermassive black holes affect the surrounding galactic neighborhood.  Centaurus A, at 12 million light years away in the southern constellation Centaurus, is known as being the most prominent radio galaxy in the sky.  The bright core of the galaxy emits extremely large and strong amounts of radio energy which is believed to be evidence of a supermassive black hole roughly 100 million times more massive than the Sun.  Black holes often have eyes bigger than their stomachs and swallow more matter from the galaxy than they can handle and the excess matter gets blasted out millions of miles into space in massive jets of radiation, in this case, radio energy.  Evidence of the jets can be seen in the upper left portion of the image where there is a thin redish filament.  When imaged through red, blue, and green filters we can see the optical portion of the radio jets where there are high levels of oxygen and hydrogen and young star formation.

Centaurus A or NGC 5128 Credit: MPG/ESO

Since Centaurus A is an elliptical galaxy it has all the markings a good elliptical should have…a bright core and a almost uniformly distributed cloud of stars which are older and cooler than stars in spiral galaxies.  However, Centaurus A is a strange one in that it has a dark band of cloud obscuring the galaxy’s core.  The cloud is the same kind of cloud you would see in a typical spiral galaxy with spiral arms.  These clouds are rich in the stellar building block element hydrogen which glows red within the cloud.  Here stars are being formed within the clouds and this part of the galaxy is much younger than the rest of the elliptical part.  This seems to be the leftover of a massive collision or interaction between the giant elliptical and a less massive spiral galaxy.  The spiral picked a fight it couldn’t win and is in the process of being ripped apart by the elliptical.

Score another awesome image for the European Southern Observatory!  The joint government institution is celebrating its 50th anniversary this year.  Many happy returns and many more awe-inspiring and educational images to come!

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