[Music]
Narrator: The large Magellanic Cloud is among the closest galaxies to our own Milky Way,
offering astronomers a detailed look at what makes a galaxy tick.
One of its most striking features is the Tarantula Nebula,
a star-forming region than any in ours or other
neighboring galaxies. This is the source of most of the gamma rays
we see from the LMC. Astronomers had thought the emission was a byproduct of
star formation, which includes short-lived massive stars whose explosions
produce shockwaves that can accelerate particles. Interactions by these
particles, called cosmic rays, can produce gamma rays, the highest-energy
form of light. But a discovery by NASA's Fermi Gamma-ray
Space Telescope has turned this thinking on its head. Most of the
emission arises from a single gamma-ray pulsar--the first ever detected in
another galaxy. Pulsar J0540-6919
turns out to be the most luminous gamma-ray
pulsar yet observed, beating the previous record holder, the famous Crab
Neubula pulsar in the Milky Way by 20 times.
Discovered in X-rays using NASA's Einstein satellite in 1984,
J0540 looked like a twin of the Crab until Fermi's Large Area
Telescope unveiled its gamma-ray power. While Fermi is the most
sensitive gamma-ray telescope ever launched, its vision is not as sharp as
telescopes using other wavelengths. In 1998,
NASA's RXTE satellite detected X-ray pulses from J0537-6910,
a pulsar located just 16 arcminutes from J0540,
or about half the apparent width of the Moon. In the early years of Fermi's
mission, the two pulsars were seen only as a single steady gamma-ray source.
But the vision of Fermi's Large Area Telescope
improves over time for two reasons. First, it collects more
gamma rays, and each one adds to the story of cosmic sources.
Second, Fermi scientists improve their knowledge of the instrument, allowing them to
reanalyze existing data to tease out more detail.
Thanks to new data, and a reprocessing of old, Fermi scientists
were finally able to detect gamma-ray pulses from J0540,
revealing its incredible luminosity. The object is responsible for
perhaps 60 percent of the gamma rays from the Tarantula Nebula.
The surprise that it's the pulsar, not the nebula, suggests astronomers need to
revisit their understanding of how cosmic rays are produced and move through
star-forming regions. And the best way to do that, of course, is to
keep watching the sky.
[Beeping]