In this lecture we'll learn about gamma-ray
bursts, and what astronomers think is the
cause of these amazingly energetic celestial
events.
Until recently, gamma-ray bursts were one
of the biggest mysteries in high-energy astronomy.
They were discovered serendipitously in the
late 1960s by U.S. military satellites which
were looking for Soviet nuclear testing that
was in violation of the atmospheric nuclear
test ban treaty.
Since nuclear explosions produce gamma rays,
the satellites used gamma ray detectors.
They didn't find any violations of the nuclear
treaty, but they did discover bright bursts
of gamma rays from beyond the solar system.
Observations in the 1990s showed that many
gamma-ray bursts were coming from very distant
galaxies.
Instrumentation on newer satellites like the
Swift satellite and the Fermi Gamma-ray Space
Telescope (shown here) indicate that the energy
behind a gamma-ray burst comes from the collapse
of matter into a black hole.
There are two types of gamma-ray bursts.
Long-duration bursts last anywhere from 2
seconds to several minutes, with an average
time of about 30 seconds.
They are associated with the deaths of massive
stars in supernovae, although not every supernova
produces a gamma-ray burst.
Short duration bursts are those that last
less than 2 seconds.
These bursts appear to be associated with
the merger of two neutron stars into a new
black hole, or a neutron star with a black
hole to form an even larger black hole.
Gamma-ray bursts shine hundreds of times brighter
than a typical supernova and about a million
trillion times as bright as the Sun, making
them briefly the brightest source of cosmic
gamma-ray photons in the observable Universe.
Gamma-ray bursts are detected roughly once
per day from completely random directions
of the sky
The stars linked to them are typically on
the order of billions of light years away.
The Earth itself is about 4.5 billion years
old, so some gamma-ray bursts occurred when
our planet was still a fiery newborn, before
the first microbes formed, and even before
the oceans had formed.
Some gamma-ray bursts that we have observed
actually originated while the universe was
only a few billion years old.
That's all for gamma-ray bursts, and for the
bizarre stellar graveyard.
Take care, I'll talk to you again soon.
