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Crab Nebula

January 6, 2012

More than 950 years ago, a star announced its death to startled Earthlings in dramatic fashion — as a brilliant new star in the constellation Taurus. It was bright enough to see in daylight for weeks.

The star left behind an expanding, glowing cloud of debris that resembles the outline of a crab. It’s faint and tough to see without a good telescope. But tonight, you can see its location in the sky thanks to the Moon. It’s to the lower right of the Moon in early evening, and the Moon sits almost directly in front of it a couple of hours before sunrise.

The remnant is known as M1, the Crab Nebula.

The nebula was born when a heavy star exploded as a supernova. The star’s outer layers are still racing outward at millions of miles an hour, so they’ve spread out to form a cloud that’s several light-years in diameter.

At the center of the cloud is the star’s crushed core — a neutron star. Its material is so dense that a chunk the size of a sugar cube would weigh billions of tons.

The explosion that created the nebula also caused the neutron star to spin more than 30 times a second. And it created a magnetic field a trillion times stronger than Earth’s. As the star spins, the magnetic field causes it to beam energy into space. Radio telescopes detect this beam as on-and-off “pulses” of energy, so the neutron star is also known as a pulsar. We’ll have more about pulsars tomorrow.


Script by Damond Benningfield, Copyright 2011


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