Wonders of the Universe - Brian Cox [51]
Once this brief cosmic light show is over, an average-sized star will shrink to an object no bigger than Earth. A white dwarf is the fate of such stars and billions like it, but for massive stars like Betelgeuse the action is far from over. If a star has a mass half as big again as our Sun, it will continue down the chemical production line. As helium fusion slowly comes to an end, gravity takes over and the collapse of the core restarts. The temperature rises, launching the third stage in the birth of our universe’s elements, and with temperatures reaching hundreds of millions of Kelvin, carbon fuses with helium to make neon, neon fuses with more helium to make magnesium, and two carbon atoms fuse to make sodium. With more and more elemental ingredients entering the cooking pot, and temperatures rising, the heavier elements are produced one after another. The core continues to collapse, the temperature continues to rise, and the next stage of fusion begins, leaving layers of newly minted elements behind.
With the first twenty-five elements now created within the star, the runaway production line hits a block at the twenty-sixth element, iron, created from a complex cascade of fusion reactions fuelled by silicon. At this stage the temperature of the star is at least 2.5 billion Kelvin, but it has nowhere else to go. The peak of nuclear stability has been reached, and no more energy can be released by adding more protons or neutrons to iron. The final stage of iron production lasts only a couple of days, transforming the heart of the star into almost pure iron in a desperate bid to release every last gasp of nuclear binding energy and stave off gravity. This is where the fusion process stops; once the star’s core has been fused into iron, it has only seconds left to live. Gravity must now win, and the star collapses under its own weight forming a planetary nebula.
As I walked away from the prison for the cameras, a button was pressed and the building fell. The demolition took seconds – the same time it takes a red giant star like Betelgeuse to collapse
PLANETARY NEBULAE
This dying star, IC 4406, like many planetary nebulae, is highly symmetrical. It is known as the ‘Retina Nebula’ because the tendrils of dust emitted from it that have been compared to the eye’s retina.
NASA
About 5,000 light years (4,700 trillion kilometres/2,900 trillion miles) from Earth lies the Calabash Nebula. This image, captured by the Hubble Space Telescope, shows material being ejected from the star.
The Eskimo Nebula is so-called because of its resemblance to a head surrounded by fur-lined hood when viewed from Earth. It was discovered in 1787 by astronomer William Herschel.
This composite image depicts the Helix Nebula. This planetary nebula resembles a doughnut, as seen from Earth, but new evidence suggests that the Helix in fact consists of two gaseous discs.
MyCn18 is a young planetary nebula which was discovered in the early twentieth century. However, it was this Hubble Telescope image in January 1996 that revealed the nebula’s hourglass shape with intricate engravings.
NASA
The aptly named Cat’s Eye Nebula (officially known as NGC 6543) was one of the first planetary nebulae to be discovered (in 1786 by William Herschel). It is one of the most complex nebulae known to exist in the Universe.
Imaged on 20 July 1997, Mz3 has been dubbed the Ant Nebula because its outline resembles the head and thorax of an ant when seen through telescopes on Earth. On close inspection, the ant’s body appears to consist of two fiery lobes.
This planetary nebula is known as Kohoutek 4-55 (or K 4-55), named after its discoverer, Czech astronomer Lubos Kohoutek. It is unusual for its multi-shell structure.
THE RAREST OF ALL
Once the centre of the great American gold rush, the 16-1 mine is one of the few gold mines still operating in the state of California today. Digging for gold