Starship Asterisk*

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The beautiful, petal-like shells of galaxy PGC 6240 are captured here in intricate detail by the NASA/ESA Hubble Space Telescope, set against a sky full of distant background galaxies. This cosmic bloom is of great interest to astronomers due to both its uneven structure, and the unusual clusters of stars that orbit around it — two strong indications of a galactic merger in the recent past.

PGC 6240 is an elliptical galaxy that resembles a pale rose in the sky, with hazy shells of stars encircling a very bright centre. Some of these shells are packed close to the centre of the galaxy, while others are flung further out into space. Several wisps of material have been thrown so far that they appear to be almost detached from the galaxy altogether.

Astronomers have studied PGC 6240 in detail due to this structure, and also because of its surrounding globular clusters — dense, tightly packed groups of gravitationally bound stars that orbit galaxies. Over 150 of these clusters orbit our own galaxy, the Milky Way, all composed of old stars.

All the globular clusters around a certain galaxy form at approximately the same time, giving them all the same age. This is echoed within the clusters — all the stars within a single cluster form at around the same time, too. Because of this, most galaxies have cluster populations of pretty similar ages, both in terms of overall cluster, and individual stars. However, PGC 6240 is unusual in that its clusters are varied — while some do contain old stars, as expected, others contain younger stars which formed more recently.

The most likely explanation for both the galaxy’s stacked shell structure and the unexpectedly young star clusters is that PGC 6240 merged with another galaxy at some point in the recent past. Such a merger would send ripples through the galaxy and disrupt its structure, forming the concentric shells of material seen here. It would also ignite a strong burst of star formation in the galaxy, which would then trigger similar activity in nearby space — leading to the creation of new, younger globular clusters around PGC 6240.

PGC 6240 is an elliptical galaxy in the southern constellation of Hydrus (The Water Snake). Also visible in this region are numerous background galaxies, speckled across the sky behind PGC 6240. Even though these bodies are at such vast distances from us, it is possible to make out the structure of many of the galaxies, especially the small spirals that stand out colourfully against the dark sky.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.

Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt

bystander wrote:Soft Shells and Strange Star Clusters
ESA/HEIC Hubble Photo Release | 2013 Oct 10

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The beautiful, petal-like shells of galaxy PGC 6240 are captured here in intricate detail by the NASA/ESA Hubble Space Telescope, set against a sky full of distant background galaxies. The most likely explanation for both the galaxy’s stacked shell structure and the unexpectedly young star clusters is that PGC 6240 merged with another galaxy at some point in the recent past. Such a merger would send ripples through the galaxy and disrupt its structure, forming the concentric shells of material seen here. It would also ignite a strong burst of star formation in the galaxy, which would then trigger similar activity in nearby space — leading to the creation of new, younger globular clusters around PGC 6240.

PGC 6240 is an elliptical galaxy in the southern constellation of Hydrus (The Water Snake). A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.

Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt

http://www.universetoday.com/105429/a-crash-put-plutos-moons-into-odd-orbits-study/#more-105429 wrote:

[b][color=#0000FF][size=125]Pluto’s solar system in a 2012 artist’s conception. P4 and P5 are now called Kerberos and Styx, respectively.[/size] Credit: NASA/John Hopkins University Applied Physics Laboratory[/color][/b]

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A Crash Put Pluto’s Moons Into Odd Orbits: Study
by Elizabeth Howell, Universe Today, October 10, 2013

<<A smash-up that created Pluto’s largest moon, Charon, likely sprayed debris four billion years ago that formed the genesis of the other moons scientists are spotting today, a new study concludes. The find could explain why the satellites Styx, Nix, Kereberos and Hydra have orbital periods that are, respectively, just about exactly 3, 4, 5 and 6 times longer than Charon’s, scientists said.

“Any initially surviving satellites would likely be destroyed in collisions, but these shattered moons wouldn’t be lost; rather, their remains would stay in the Pluto/Charon system and become the starting point for building new satellites,” stated the Southwest Research Institute (SWRI), which led the study. In modeling the destruction of the satellites, the SWRI study found that there may be a method for moving them, or their building blocks, outward, due to the competing effects of Charon’s gravitational kicks and collisions among the debris of the disrupted satellites.”

Given Charon’s large size relative to Pluto (it’s a tenth of the dwarf planet’s size, compared to the Earth-Moon 81: 1 ratio), its large mass could easily perturb these smaller moons if they got close. Also, collisions between the debris could alter the orbits “to keep things away from Charon”, the scientists said. Hopefully we will learn more when the NASA New Horizons spacecraft arrives at Pluto in 2015. The findings were presented yesterday (Oct. 9) at the American Astronomical Association’s division of planetary sciences meeting in Denver; information on whether the results are peer-reviewed was not immediately available.>>

neufer wrote:
A Crash Put Pluto’s Moons Into Odd Orbits: Study
by Elizabeth Howell, Universe Today, October 10, 2013

bystander wrote:
Not sure what this has to do with PGC 6240

Ann wrote:

Click to view full size image

NGC 2782. Photo: SDSS

PGC 6240 is very similar to NGC 2782. Presumably similar processes have led to the shaping of these galaxies.

Click to view full size image

NGC 6240. Photo:
http://photojournal.jpl.nasa.gov/catalog/PIA11828

And by the way... PGC 6240. I definitely recognize the number 6240, though with an "NGC", not a "PGC", in front of it. So isn't NGC 6240 also an interesting galaxy? Yes, you bet it is!!!


Ann

geckzilla wrote: