Bullets and tails
The interstellar and circumstellar gas around stars is far from homogeneous and contains very dense clumps of gas embedded in a lower density medium. Stellar outbursts can also explosively eject clumps as "bullets" into the surrounding medium. Relative motion between the clumps and the surroundings leads to material being stripped off the clumps, and long "tails" form behind them. Very little detailed work has been done on the generation of these tails, but the details of the interaction will have consequences for the evolution of many astrophysical sources, including wind-blown bubbles, supernova remnants, and starburst superwinds. |
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The image above right shows part of the rim of the Helix nebula, a planetary nebula surrounding a dying low mass star (off the top right of the image). Many tails can be seen - there is some controversy as to whether the tails are simply "shadows" behind the dense clumps, or are stripped material from them. I argue in a recent paper that the latter explanation is more likely.
Not dis-similar morphology is seen in an image of the "Orion bullets" shown below, which in turn bears similarity to the tails formed behind the bullets ejected from Eta Carinae.
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I have published several papers that examine the interaction of material stripped from clumps with a background flow. The image below left shows the density structure resulting from 5 sources of mass injection, while the image below center shows the injected material (black) and background material (white).
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The image above right zooms in on the two right-most clumps. The bow-shock, contact discontinuity, and reverse shock around each clump are easily identifiable. The stripped material from each clump interacts downstream with that from neighbouring clumps. The eventual mixing of this material into the background flow is a key issue which is not well understood at present.
Filaments in the Intracluster Medium
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Tails are also seen on much larger scales. The image below shows filamentary structure surrounding the central, dominant galaxy in the Perseus cluster. It is not known whether this material cooled out of the superhot gas which the galaxies are embedded in, or whether it was expelled out of the central galaxy by a superwind and/or AGN activity. Its origin has implications for our understanding of the past history of such clusters, and for their future evolution. Both of these questions are very hot topics in astronomy at present.
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