Credit
X-ray: NASA/CXC/IAA-CSIC/N.Ruiz et al,
Optical: NASA/STScI
Stars like the Sun can become remarkably photogenic at the end of their life. A good example is NGC 2392, which is located about 4,200 light years from Earth. NGC 2392, (nicknamed the "Eskimo Nebula") is what astronomers call a planetary nebula. This designation, however, is deceiving because planetary nebulas actually have nothing to do with planets. The term is simply a historic relic since these objects looked like planetary disks to astronomers in earlier times looking through small optical telescopes.
Instead, planetary nebulas form when a star uses up all of the hydrogen in its core -- an event our Sun
will go through in about five billion years. When this happens, the
star begins to cool and expand, increasing its radius by tens to
hundreds of times its original size. Eventually, the outer layers of the
star are carried away by a 50,000 kilometer per hour wind, leaving
behind a hot core. This hot core has a surface temperature of about
50,000 degrees Celsius, and is ejecting its outer layers in a much
faster wind traveling six million kilometers per hour. The radiation
from the hot star and the interaction of its fast wind with the slower
wind creates the complex and filamentary shell of a planetary nebula.
Eventually the remnant star will collapse to form a white dwarf star.
Now days, astronomers using space-based telescopes are able to
observe planetary nebulas such as NGC 2392 in ways their scientific
ancestors probably could never imagine. This composite image of NGC 2392
contains X-ray data from NASA's Chandra X-ray Observatory in purple
showing the location of million-degree gas near the center of the
planetary nebula. Data from the Hubble Space Telescope show — colored
red, green, and blue — the intricate pattern of the outer layers of the
star that have been ejected. The comet-shaped filaments form when the
faster wind and radiation from the central star interact with cooler
shells of dust and gas that were already ejected by the star.
The observations of NGC 2392 were part of a study of three planetary
nebulas with hot gas in their center. The Chandra data show that NGC
2392 has unusually high levels of X-ray emission compared to the other
two. This leads researchers to deduce that there is an unseen companion
to the hot central star in NGC 2392. The interaction between a pair of binary stars
could explain the elevated X-ray emission found there. Meanwhile, the
fainter X-ray emission observed in the two other planetary nebulas in
the sample — IC 418 and NGC 6826 — is likely produced by shock fronts
(like sonic booms) in the wind from the central star. A composite image
of NGC 6826 was included in a gallery of planetary nebulas released in 2012.
A paper describing these results is available online
and was published in the April 10th, 2013 issue of The Astrophysical
Journal. The first author is Nieves Ruiz of the Instituto de Astrofísica
de Andalucía (IAA-CSIC) in Granada, Spain, and the other authors are
You-Hua Chu, and Robert Gruendl from the University of Illinois, Urbana;
Martín Guerrero from the Instituto de Astrofísica de Andalucía
(IAA-CSIC) in Granada, Spain, and Ralf Jacob,Detlef Schönberner and
Matthias Steffen from the Leibniz-Institut Für Astrophysik in Potsdam
(AIP), Germany.
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.
Fast Facts for NGC 2392:
Scale: Image is 1 arcmin across (about 1.2 light years)
Category: White Dwarfs & Planetary Nebulas
Coordinates (J2000): RA 07h 29m 10.80s | Dec +20 54 42.50
Constellation: Gemini
Observation Date: 09 Sep 2007
Observation Time: 15 hours 57 min
Obs. ID: 7421
Instrument: ACIS
Also Known As: Eskimo Nebula
References: Ruiz, N. et al, 2013, ApJ, 767, 35; arXiv:1302.3886
Color Code: X-ray (Pink), Optical (Red, Green, Blue)
Distance Estimate: About 4,200 light years
