In the 1st year of the period Chih-ho, the 5th moon, the
day chi-ch'ou, a guest star appeared...
Yang Wei-T'e, Imperial Astronomer of the Sung Dynasty, 1054 A.D.
The Death Throes of Stars; The Most Violent Explosions in the Universe Today
Starting July 4, 1054 A.D., the people of the world were
treated to an astonishing spectacle. A new star appeared
in the sky. For 23 days, it was visible even during
daylight. The star gradually faded following its
appearance on July 4. After a little more than a year, the
event was over entirely. It could no longer be seen, even
at night. Its brief glory was recorded by Chinese and
Korean astronomers, as well as American Indians of the
Southwest United States. The witnesses to that singular
event in 1054 were seeing a Supernova.
We've seen that old stars use up their fuel, cool off, and settle down into a White Dwarf, Neutron Star, or Black Hole. This usually doesn't happen very peacefully, however. The cooling is like a chair being tipped over. It is steady until it reaches the tipping point. Once it passes that point, it goes faster and faster. Soon, however, the inner layers of the star—its most dense part—will be stopped from falling by electron or neutron degeneracy pressure as the core changes into a miniature White Dwarf or Neutron Star. The falling matter from above will suddenly crash into this inner layer, and change too. The fall and crash happens in just seconds. All this sudden crashing and changing gives off enormous amounts of energy. That energy heats up the outer layers of the star and blows them out into space with fantastic speed. At its peak, a typical supernova might shine ten billion times more brightly than our Sun! Luckily, we are usually far enough away that this isn't too bright.
With such sudden movements of matter, the intense warpage
of spacetime will change drastically and quickly. It
should not be surprising, then, if gravitational waves are
given off by a supernova. In fact, gravitational waves
will only come out if the supernova has some
"asymmetry"—that is, only if the supernova has
bumps. This will likely happen, for example, if the
original star was rotating very quickly. Fortunately, we
expect most supernovae to go off in this way. Then, the
gravitational waves will come out as one big—though
brief—burst.
Carl Sagan said, "We are star stuff." He meant that we are made of matter that came from the stars. The Oxygen we breathe, the Carbon found in every cell in our bodies, the Calcium in our bones... all of this was formed in stars. Without supernovae to blow all this star stuff into the wide cosmos, however, it would all still be trapped deep inside of those stars. These most violent of explosions breathe life into the Universe.
We've seen that old stars use up their fuel, cool off, and settle down into a White Dwarf, Neutron Star, or Black Hole. This usually doesn't happen very peacefully, however. The cooling is like a chair being tipped over. It is steady until it reaches the tipping point. Once it passes that point, it goes faster and faster. Soon, however, the inner layers of the star—its most dense part—will be stopped from falling by electron or neutron degeneracy pressure as the core changes into a miniature White Dwarf or Neutron Star. The falling matter from above will suddenly crash into this inner layer, and change too. The fall and crash happens in just seconds. All this sudden crashing and changing gives off enormous amounts of energy. That energy heats up the outer layers of the star and blows them out into space with fantastic speed. At its peak, a typical supernova might shine ten billion times more brightly than our Sun! Luckily, we are usually far enough away that this isn't too bright.
The Supernova that Kepler saw in 1604, as it appears
to us today. This image is a combination of pictures
taken by the Hubble Space Telescope, the Spitzer
Infrared Space Telescope, and the Chandra X-Ray Space
Telescope.
Carl Sagan said, "We are star stuff." He meant that we are made of matter that came from the stars. The Oxygen we breathe, the Carbon found in every cell in our bodies, the Calcium in our bones... all of this was formed in stars. Without supernovae to blow all this star stuff into the wide cosmos, however, it would all still be trapped deep inside of those stars. These most violent of explosions breathe life into the Universe.
