Swan song for stars and cameras

PN K 4-55 (Kohoutek 4-55)

A planetary nebula, a glowing shell of material thrown off by a star. A small central region of greenish clouds is encircled by a glowing, jagged ring, like a hole torn in fabric. A band of silvery-blue clouds outside this is again encircled by a larger, fainter yellow ring of gas. Puffy, smoky clouds of orange and red gas billow out from there into a large oval nebula, fading into the dark background of space. Credit: ESA/Hubble & NASA, K. Noll

Planetary nebulae are the spectacular final display at the end of a giant star’s life. Once a red giant star has exhausted its available fuel and shed its last layers of gas, its compact core will contract further, enabling a final burst of nuclear fusion. The exposed core reaches extremely hot temperatures, radiating very energetic ultraviolet light that energises the enormous clouds of cast-off gas. Molecules in the gas are ionised and glow brightly; here, red and orange indicate nitrogen molecules, green is hydrogen and blue shows oxygen in the nebula. Kohoutek 4-55 has an uncommon, multi-layered form: a bright inner ring is surrounded by a fainter layer of gas, all wrapped in a broad halo of ionised nitrogen. The spectacle is bittersweet, as the brief phase of fusion in the core will end after mere tens of thousands of years, leaving a white dwarf that will never illuminate the clouds around it again.

This image itself is also a swan song, the final work of one of Hubble’s instruments: the Wide Field and Planetary Camera 2 (WFPC2). Installed in 1993 to replace the original Wide Field and Planetary Camera, WFPC2 was responsible for some of Hubble’s most enduring images and fascinating discoveries. It in turn was replaced by the Wide Field Camera 3 in 2009, during Hubble’s final servicing mission. The data for this image were taken a mere ten days before the instrument was removed from the telescope, as a fitting send-off for WFPC2 after 16 years’ work. The latest and most advanced processing techniques have been used to bring the data to life one more time, producing this breathtaking new view of Kohoutek 4-55.

Source: ESA/Hubble/potw

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Dying star offers glimpse of our Sun’s future

Dying star offers glimpse of our Sun’s future
Copyright: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

Acknowledgment: R. Sahai and J. Trauger (Jet Propulsion Laboratory)

 Hi-res JPG - Hi-res TIFF

This is a final act of celestial beauty before the long fade into cosmic history. Invisibly buried in the centre of this colourful swirl of gas is a dying star, roughly the same mass as the Sun.

As a star ages, the nuclear reactions that keep it shining begin to falter. This uncertain energy generation causes the stars to pulsate in an irregular way, casting off its outer layers into space.

As the star sheds these outer gases, the super-hot core is revealed. It gives off huge quantities of ultraviolet light, and this radiation causes the gas shells to glow, creating the fragile beauty of the nebula.

This example is known as Kohoutek 4-55. Named after its discoverer, the Czech astronomer Luboš Kohoutec, it is located 4600 light years from Earth, in the direction of the constellation Cygnus.

This image was the final ‘pretty picture’ taken by the Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2). The camera was installed in 1993 and worked until 2009, offering a 16-year stretch of unparalleled observations.

WFPC2 took many of Hubble’s iconic images. They helped to make the space telescope a household name across the world.

This particular shot is a composite of three images, each taken at a specific wavelength to isolate the light coming from particular atoms of gas. The different wavelengths have been colour-coded to aid recognition.

Red signifies nitrogen gas, green shows hydrogen and blue represents oxygen. The whole sequence was captured in 2 hours on 4 May 2009.

The intricate swirls of gas offer us a glimpse of our Sun’s distant future. In 5 billion years’ time, our star will be dying. It is expected to behave in the same way as see here, shedding its outer layers to reveal the burning core, which then becomes a slowly cooling ember known as a white dwarf.

By that time, Earth will be long gone, burnt to a crisp as the Sun dies. But the beauty of our star’s passing will shine across the Universe.

This image was first published on the Hubble Space Telescope website on 10 May 2009.

Source: ESA