Astronomers from the VERITAS collaboration have detected an extremely energetic and unexpected blast from the Crab pulsar. Instead of being “baffled,” as I’m sure someone is going to say, these astronomers are excited about the chance to redefine how these tiny, dense objects give off so much light.
We love our pulsars here at Discovery News. After all, who can’t adore a densely-packed, highly magnetized, lighthouse-beaming ball of subatomic particles the size of a large city?
This pulsar in particular lives at the center of the Crab Nebula, both the remnants of a stellar explosion, known as a supernova, that was recorded by Chinese and Arab astronomers in 1054.
Pulsars were discovered by their radio emission, but the Crab pulsar is one that is also bright in x-ray and gamma rays, the highest forms of electromagnetic energy, or light. The gamma ray pulses coming from the Crab hit 100 giga-electron volts (GeV). Suffice to say, our biological cells would not fare well when blasted with these photons.
Our planet’s atmosphere, thankfully, protects us from this harmful radiation, but that also makes it difficult to detect these phenomena. Astronomers made clever use of a process by which a gamma ray photon interacts with the Earth’s atmosphere creating high energy particles and a flash of light known as Cerenkov radiation.
The telescopes of VERITAS are actually optical detectors that look for that tiny flash in the atmosphere and trace the the source back to its astrophysical origins.
100 GeV is too high of an energy to have been created by curvature radiation, the currently favored model of pulsar emission. This literally is created by high-energy charged particles, such as electrons, moving along curved magnetic field lines. Another mechanism is needed to explain the recent observations, but astronomers are not without options.
In the lead for that role is inverse Compton scattering. This involves those fast-moving electrons as well. When a lower energy photon (or particle of light) gets close to such an electron, it can be “boosted” to higher energies by stealing some of the energy of the electron, slowing the latter down. Inverse Compton scattering is already seen to creates x-ray emission around supermassive black holes.
Pulsars, like black holes, are extremely dense objects that cause some strange, but perfectly natural, physical processes. Astronomers look forward to being surprised and having to go back and re-tweak their models. Just don’t physically get in the way of a gamma-ray pulse. Ouch.
Images: Top – The Crab pulsar and surrounding pulsar wind as seen by the Chandra X-ray Observatory. Credit: NASA/CXC/MSFC/M.Weisskopf et al.; Middle – an infrared look at the Crab Nebula. Credit - NASA/JPL-Caltech/R. Gehrz (University of Minnesota)