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A Reborn Planetary Nebula
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[تصویر:  13531498171.jpg]





These images of the planetary nebula Abell 30, (a.k.a. A30), show one of
the clearest views ever obtained of a special phase of evolution for
these objects. The inset image on the right is a close-up view of A30
showing X-ray data from NASA's Chandra X-ray Observatory in purple and
Hubble Space Telescope (HST) data showing optical emission from oxygen
ions in orange. On the left is a larger view showing optical and X-ray
data from the Kitt Peak National Observatory and ESA's XMM-Newton,
respectively. In this image the optical data show emission from oxygen
(orange) and hydrogen (green and blue), and X-ray emission is colored
purple.




A planetary nebula -- so called because it looks like a planet when
viewed with a small telescope -- is formed in the late stage of the
evolution of a sun-like star. After having steadily produced energy for
several billion years through the nuclear fusion of hydrogen into helium
in its central region, or core, the star undergoes a series of energy
crises related to the depletion of hydrogen and subsequent contraction
of the core. These crises culminate in the star expanding a
hundred-fold to become a red giant.




Eventually the outer envelope of the red giant is ejected and moves away
from the star at a relatively sedate speed of less than 100,000 miles
per hour. The star meanwhile is transformed from a cool giant into a
hot, compact star that produces intense ultraviolet (UV) radiation and a
fast wind of particles moving at about 6 million miles per hour. The
interaction of the UV radiation and the fast wind with the ejected red
giant envelope creates the planetary nebula, shown by the large
spherical shell in the bigger image.




In rare cases, nuclear fusion reactions in the region surrounding the
star’s core heat the outer envelope of the star so much that it
temporarily becomes a red giant again. The sequence of events --
envelope ejection followed by a fast stellar wind -- is repeated on a
much faster scale than before, and a small-scale planetary nebula is
created inside the original one. In a sense, the planetary nebula is
reborn.




The large nebula seen in the larger image has an observed age of about
12,500 years and was formed by the initial interaction of the fast and
slow winds. The cloverleaf pattern of knots seen in both images,
correspond to the recently ejected material. These knots were produced
much more recently, as they have an observed age of about 850 years,
based on observations of their expansion using HST.




The diffuse X-ray emission seen in the larger image and in the region
around the central source in the inset is caused by interactions between
wind from the star and the knots of the ejected material. The knots are
heated and eroded by this interaction, producing X-ray emission. The
cause of the point-like X-ray emission from the central star is unknown.





Studies of A30 and other planetary nebulas help improve our
understanding of the evolution of sun-like stars as they near the end of
their lifetime. The X-ray emission reveals how the material lost by the
stars at different evolutionary stages interact with each another.
These observations of A30, located about 5500 light years away, provide a
picture of the harsh environment that the solar system will evolve
towards in several billion years, when the sun's strong stellar wind and
energetic radiation will blast those planets that survived the
previous, red giant phase of stellar evolution.




The structures seen in A30 originally inspired the idea of reborn
planetary nebulas, and only three other examples of this phenomenon are
known. A new study of A30,
using the observatories mentioned above, has been reported by an
international team of astronomers in the August 20th, 2012 issue of The
Astrophysical Journal.




The first author of the paper reporting these results is Martín A.
Guerrero of the Instituto de Astrofísica de Andalucía (IAA-CSIC) in
Spain. The other authors are N. Ruiz, also from the IAA-CSIC, Spain;
W.-R. Hamann, from the University of Potsdam, Germany; Y.-H. Chu, from
the University of Illinois, Urbana, IL; H. Todt, from the University of
Potsdam, Germany; D. Schönberner, from the Leibniz-Institut Für
Astrophysik in Potsdam, Germany; L. Oskinova, from the University of
Potsdam, Germany; R. Gruendl, from the University of Illinois, Urbana,
IL; M. Steffen, from the Leibniz-Institut Für Astrophysik in Potsdam,
Germany; W. Blair, from Johns Hopkins University in Baltimore, MD and J.
Toalá from the IAA-CSIC, Spain.




NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and
flight operations from Cambridge, Mass.




Credits: Inset X-ray (NASA/CXC/IAA-CSIC/M.Guerrero et al); Inset Optical
(NASA/STScI); Widefield X-ray (ESA/XMM-Newton); Widefield Optical
(NSF/NOAO/KPNO)




› Read more/access all images


› Chandra's Flickr photoset




J.D. Harrington, 202-358-0321
Headquarters, Washington
j.d.harrington@nasa.gov

Janet Anderson, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.
janet.l.anderson@nasa.gov

Peter Edmonds, 617-571-7279
Chandra X-ray Center, Cambridge, Mass.
pedmonds@cfa.harvard.edu
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