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Narrator: Hidden deep within a group
of ancient stars, there lurks a young and powerful enigma.
This is NGC 6624, a globular cluster near our
galaxy's center thought to be about 10 billion years old. NASA's
Fermi Gamma-ray Space Telescope detects high-energy radiation from many
globular clusters. Usually what Fermi is seeing is the cumulative gamma
rays from all of the old pulsars in these clusters. A pulsar
is a rapidly spinning neutron star, which is the small, incredibly dense
remnant of a much more massive star. A teaspoon of matter from a neutron
star weighs as much Mount Everest, and a neutron star is so compact
that a ball about 15 miles across contains more matter than our sun.
Neutron stars spin between 7 and 40,000 times a minute
and form with incredibly strong magnetic fields. Rapid spin and
intense magnetic fields drive powerful beams of electromagnetic radiation,
including gamma rays. As the pulsar rotates, these beams
sweep the sky like a lighthouse. To a distant observer, the pulsar appears
to blink on and off. Pulsars slow down as they age
but some of the oldest pulsars spin hundreds of times a second. Each of
these millisecond pulsars orbits a normal star. Over time, the impact
of gas pulled from the normal star, has spun the pulsar up to incredible speeds.
This accretion may be the cause of their weaker magnetic
fields. Despite this, these pulsars also emit gamma rays.
But the millisecond pulsar in NGC 6624
doesn't fit neatly into this picture. It's so bright that Fermi
directly detects its gamma rays, and so far it's the only one seen in a globular
cluster with such power. It's losing energy so fast that it must be only
around 25 million years old--the youngest millisecond pulsar ever found.
It also possesses the strongest magnetic field yet observed in a
millisecond pulsar. It's high energy output dooms it to fade out quickly
on astronomical time scales and scientists wonder if this object represents
a new way to make millisecond pulsars.
In three years, Fermi has detected more
than 100 gamma-ray pulsars, shown here using animated pulses
fifty slower than actual speed. Recent advances in data
analysis helped Fermi reach this milestone, and these techniques promise to find many more
gamma-ray pulsars. Some of these are historical
--the first gamma-ray pulsars ever discovered. Others,
like the pulsar in NGC 6624, were first seen by radio
telescopes and then observed by Fermi. Some were first spotted in
radio after investigating unknown sources detected by Fermi. And about a
third of gamma-ray pulsars were discovered by Fermi on the basis of their gamma-ray
pulsations alone. Fermi's gamma-ray observations are literally showing us
these incredible stellar lighthouses in a new light.
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