A pulsar that is able, without warning, to dramatically change the way in which it shines has been identified by an international team of astronomers.
using a satellite X-ray telescope combined with terrestrial radio telescopes.
The pulsar was found to flip on a roughly half-hour timescale between two extreme states; one dominated by X-ray pulses, the
other by a highly-organised pattern of radio pulses.
Pulsars - small spinning stars that are about the size of a city, around 20 km in diameter - emit oppositely directed beams
of radiation from their magnetic poles. Just like a lighthouse, as the star spins and the beam sweeps repeatedly past the
Earth we see a brief flash.
A pulsar with glowing cones of radiation stemming from its magnetic poles. New observations reported in
Science re-open an old debate about how these spinning stars work. (Credit: European Space Agency/ATG medialab)
Some pulsars produce radiation across the entire electromagnetic spectrum, including at X-ray and radio wavelengths.
Despite being discovered more than 45 years ago the exact mechanism by which pulsars shine is still unknown.
To find out if the X-rays could also flip the scientists studied a particular pulsar called PSR B0943+10 with radio pulses which
change in form and brightness every few hours with some of the changes happening within about a second.
"The behaviour of this pulsar is quite startling, it's as if it has two distinct personalities," Dr Ben Stappers from The
University of Manchester's School of Physics and Astronomy said.
"As PSR B0943+10 is one of the few pulsars also known to emit X-rays, finding out how this higher energy radiation behaves
as the radio changes could provide new insight into the nature of the emission process."
To identify the exact moment of flip in the pulsar's radio behaviour the X-ray observations were tracked simultaneously
with two of the largest radio telescopes in the world, LOFAR and the GMRT.
"As well as brightening in the X-rays we discovered that the X-ray emission also shows pulses, something not seen when
the radio emission is bright," Dr Stappers added.
This was the opposite of what we had expected. I've likened the changes in the pulsar to a chameleon. Like the animal
the star changes in reaction to its environment, such as a change in temperature." Geoff Wright from the University of Sussex said.
"Our observations strongly suggest that a temporary "hotspot" appears close to the pulsar's magnetic pole which switches on and
off with the change of state. But why a pulsar should undergo such dramatic and unpredictable changes is completely unknown."