Return to my Astronomy/Space pages
Go to my home page
Supernova 1054
© Copyright 1999, Jim Loy
On July 4, 1054, a bright star appeared in the sky. For 23 days, it was
bright enough to be seen in the daytime. It gradually dimmed, until it was no
longer visible on April 17, 1056. This new star was recorded in China and
Japan. No record of it has been found in Korea (the records were probably
lost), Europe, or the Arab countries. Such a new star is now called a
supernova, an exploding star which is brighter than all the rest of the stars
of the galaxy, put together.
The new star was recorded to be near Zeta Tauri, a dim
star. Today, near Zeta Tauri is the Crab Nebula (see the Palomar Mountain photo
on the left), also known as M1. This is an irregular splotch of gasses, which
bears a slight resemblance to a crab. It is called M1, because it is first on
Messier's list of fuzzy objects (nebulas, clusters, and galaxies) that might be
mistaken for a comet. Messier was a comet fanatic, having discovered a few
comets. But nowadays he is famous for his list. The Crab Nebula is not exactly
where the Chinese records say the star was, but it is very close. The nebula is
expanding, and seems to have started from a point source in about the year
1140. This discrepancy of the year seems to have been explained by an
acceleration due to a magnetic field. The magnetic field is deduced from other
features of the light from the nebula, the fact that it is related to
synchrotron radiation.
The Crab Nebula is a strong source of radio waves. In 1969, the radio
waves were shown to pulse, to turn on and off, thirty times a second. It was
half-jokingly suggested that LGM (little green men) had been discovered. This
pulsing phenomenon is caused by a pulsar, a pulsing star. The pulsing is like
the light from a lighthouse, the flashing off and on of a spinning object. Near
the center of the Crab nebula is a dim star called NP0532. This star has been
shown to be the pulsar, and its visible light turns on and off at the same
frequency as the radio waves. This star is spinning at a rate of 30 times per
second, and is a tiny (about 10 km. or 6 mi. in diameter) neutron star, also
called a "supernova remnant." Such stars spin very rapidly, because they were
spinning (slowly) when they were much larger. They spin faster as they shrink,
just as a spinning figure skater spins faster by pulling his/her arms close to
his/her body.
So, we see the results of the first July 4th fireworks display, one that
was seen almost a thousand years ago.
Addendum:
The Crab Nebula is about 6000 light years away, so the actual explosion
happened about 7000 years ago, even though it was seen in 1054. Another source
says that the neutron star is 12 mi. in diameter, so I assume that there is
some uncertainty about its size.
Return to my Astronomy/Space pages
Go to my home page