Gravity's ultimate triumph

All stars live on borrowed time. They are born of gravity and, eventually, gravity destroys them. This is spectacularly true in massive stars. A star more than 10 times as heavy as the Sun rips through its nuclear fuel at a prodigious rate-in aa few million rather than a few billion year. Once a heavyweight star has exhausted its hydrogen it has sufficiently high temperatures and pressures to fuse heavier elements. But when it tries to squeeze a core made of iron, all hell breaks loose-leading to one of the most sensational explosions the Universe can provide. A supernova explosion can spawn some bizzarre descendants:a a neutron star, or even a black hole.

Going out with a bang
A few supernovas are the result of one star in a double star system dumping gas on the other, but most are heavyweight stars dying with a bang. Nuclear reactions have produced a core made of iron-which cannot be used as nuclear fuel. Fusing iron takes in energy rather than givg it out. The result is internal collapse: with the temperature soaring to 50 billion 'C(90 billion 'F), the core emits a flood of tiny energetic particles, called neutrinos, which rip the star apart.

Superdense lighthouses
A supernova's core collapses in just a few seconds, often producing a pulsar. These are superdense, rotating neutron stars that beam flashes of radiation - like a lighthouse - as they spin. Most pulsars, which are the size of a city such as London, spin about once a second, but the record is 642 times a second!

Full of neutrons
A pulsar is the ultimate in squashed matter. Th protons and electrons in the core of the former star have been squeezed to form neutrons - particles with no electrical charge. Standing shoulder to shoulder, the neutrons hold up the pulsar against the force of gravity. This compressed neutron star has a magnetic field about a trillion times more powerful than the Earth's. Its magnetic poles squirt dazzling beams of radiation into space.

Black out
Sometimes the relic left after a supernova explosion is too heavy to become a pulsar. If it weighs more than three Suns, not even the superdense neutrons can hold it up against the force of gravity. The object collapses even further to become a black.

The scale of things
A star can take a lot of squeezing. When it becomes a whtie dwarf, a star like our Sun(1.4 million km/870,000miles across) packs down to the size of Earth(12,000 km/7,500 miles across). A neutron star, weighing in at 1.5 Suns, is only 25 km(15miles) across - about the size of Manhattan Island. A black hole may be just a few kilometres in diameter.

Spot facts:

Supertanker in a pinhead
The material in a pulsar is much more compressed than in a white dwarf. Gravity squeezes it so tightly that a pinhead of pulsar material would weigh a million tonnes(tons) - twice as much as the world's biggest supertanker.

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