APOD: The Outer Shells of Centaurus A (2012 Jul 01)

[APOD Robot]

The Outer Shells of Centaurus A

Explanation: What causes the surrounding shells in peculiar galaxy Cen A? In 2002 a fascinating image of peculiar galaxy Centaurus A was released, processed to highlight a faint blue arc indicating an ongoing collision with a smaller galaxy. Another interesting feature of Cen A, however, is the surrounding system of shells, better visible here in this recently released wider pan from the four meter Blanco telescope at Cerro Tololo Inter-American Observatory. Faint shells around galaxies are not unusual and considered by themselves as evidence of a previous galaxy merger, analogous to water ripples on a pond. An unexpected attribute of these shells is the abundance of gas, which should become separated from existing stars during the collision.

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[geckzilla]

Temporary mirror for this APOD:
library/APOD/APOD%20mirror/ap120701.html

[nstahl]

I take it there's a problem with the usual APOD computer. Nothing serious I hope.

This is a great APOD, btw.

[orin stepanek]

Interesting story about the shells during a galactic merger!
And I've heard of hermit crabs using shells for a home! But kitties? Hermit Kitties?

Click to view full size image

[pssacks@hotmail.com]

Could the outer shells of Centaurus A be the result of two black holes from the merging galaxies circling one another and setting off gravity waves?

[neufer]

Could the outer shells of Centaurus A be the result of
two black holes from the merging galaxies circling one another and setting off gravity waves?

I was thinking more on the lines of:
two or more black holes from the merging galaxies circling one another and ejecting stars in all directions.

[Moonlady]

Could the outer shells of Centaurus A be the result of
two black holes from the merging galaxies circling one another and setting off gravity waves?

I was thinking more on the lines of:
two or more black holes from the merging galaxies circling one another and ejecting stars in all directions.

Oh you guys are phenomenal!


My brain stopped working when I saw this stunning Apod and I made this sound: woooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooow!

[Ann]

Click to view full size image

Photo: Wanderingdivers

I want to return to the idea of "ripples in a pond". Astrophtographer David Malin was, or so I think, the first person to notice that large elliptical galaxies are surrounded by faint shells. David Malin interpreted these shells as signs of mergers. When a smaller galaxy fell into a larger galaxy, the larger galaxy would respond by expanding. But as the galaxy rebounded and contracted again, shells of stars would remain outside the galaxy, like debris washed up on a shore.

The Cartwheel Galaxy. Photo: Hubble

The Cartwheel galaxy was hit by another galaxy, and the Cartwheel responded by taking on this strange shape. As the Cartwheel rebounds and contracts again, remnants of its outer shell will likely remain.

When large ellipticals have many outer shells, that is probably a sign that they have undergone many mergers.



Ann

[Beyond]

Now that's something to pond-der, ripples.

[StarCuriousAero]

Beautiful picture, Centaurus A has always been incredibly fascinating. I'm also glad to see it finally described as a "peculiar" galaxy... since none of those other galaxy descriptions seem to adequately fit.