Astronomie · English version

Penguin Galaxies

In the past of the Galaxy Zoo, volunteers pointed out two galaxy mergers that have a surprisingly similar shape with penguins:

First dailyzoo-post


Second dailyzoo-post


I think the similar pattern is no coincidence: There are two galaxies merging with each other. One galaxy is an elliptical galaxy without triggered star-formation and another galaxy with mainly blue stars that show strong star-formation.
Both penguin-galaxies do have the centre of the galaxy in the “head” structure. Another similar sturcture is a “bow”, which draws the head for the penguin in the first image and the tummy in the second image. This is a region of intense star-formation, maybe the most intense star-formation in those galaxies.
There are two extentions that are the “body” and “beak”. Interesting is that the “beak” in the second image does point into the direction of the elliptical galaxy.

Image information: The first image is a Hubble Space Telescope image and was the cover of Astronomy&Geophysics in October 2013. The second image is a SDSS image.

I think that both mergers consist of a massive elliptical galaxy and a less massive galaxy, which was once a spiral galaxy with two arms. The less massive spiral galaxy does miss the elliptical galaxy, while merging. But before it does miss the galaxy, one arm (beak) does interact with the elliptical galaxy. The gravitational interaction pushes the centre of the spiral galaxy forward, while the other arm (body) is left behind. The push of the gravitational interaction also forms the “bow”. This is the situation for the second SDSS image.
The spiral galaxy does not stop, it moves further and one arm (beak) loses the connection to the elliptical galaxy. Now the other arm (body) does interact with the elliptical galaxy. This is what we see in the first Hubble image.

This simple procsess does turn the penguin-galaxy around. First the “bow” was the tummy and now the back is the “bow”. But the “bow” does not move from one side to another. It is more like how we recognize the pattern of a penguin: The first penguin-galaxy in the Hubble image looks like a standing penguin with the head pointing down. The second penguin-galaxy looks like a swimming penguin with the head pointing up.


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