IC 4634, an S-shaped planetary nebula in Ophiuchus

IC 4634, an S-shaped planetary nebula in Ophiuchus

IC 4634 is a planetary nebula located over 7500 light-years away from Earth in the constellation of Ophiuchus, the Serpent Holder. It has an S-shaped structure in which the inner shell is expanding with 20 km/s.

The two shining, S-shaped ejections are from a dying central star. This star bloated as it aged and launched its outer layers off into space. The star’s very hot, exposed core has since beamed intense ultraviolet radiation at these lost shells of gas, making them glow in rich colours.

The end of a star’s life is anything but peaceful. Once the fuel source of hydrogen and helium run out for a star like our Sun, it swells to enormous size and becomes a red giant. During this process, the star puffs off bubbles of gas and forms a planetary nebula. If the star is spinning, as seen with IC 4634, symmetrical rings of material are thrown off. All that is left behind is the hot core of the dying star called a white dwarf.

Apparently, IC 4634 has experienced several episodes of symmetric ejections, with the outer S-shaped feature being related to an earlier ejection, and the outermost arclike string of knots being the relic of a still much earlier ejection. There is tantalizing evidence that the action of these collimated outflows has also taken part in the shaping of the innermost shell and inner S-shaped arc of IC 4634. The result is remarkably symmetric on each side of the central star.

On the basis of composition measurements, IC 4634 is classified as a metal-poor planetary nebula with a low-mass central star; its metallicity appears to be lower than in the Sun or the average planetary nebula. The most likely temperature of the central star in IC 4634 appears to be about 55,000 K, with a mass of about 0.55 Solar Mass. The compact size of IC 4634, its high surface brightness, and remarkable morphology make it a worthwhile object for study.

Planetary nebulae like IC 4634 are not related to planets at all. Astronomers call such an object a planetary nebula, because its round shape resembles that of the distant planets Uranus and Neptune when viewed with a small telescope.

Planetary nebulae fade gradually over tens of thousands of years. The hot, remnant stellar core will eventually cool off for billions of years as a white dwarf. Our own Sun will undergo a similar process, so, planetary nebulae could well offer a glimpse of the future that awaits our own Sun in about five billion years.

The image is taken with Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2).
Image Credit: ESA/Hubble and NASA.

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