China is set to launch a space telescope, the Hard X-ray Modulation Telescope (HXMT), to observe pulsars in the galaxy of Milky Way, according to scientists. "We are still not clear about the interior of pulsars," Zhang Shuangnan, lead scientist of HXMT and director of the Key Laboratory of Particle Astrophysics of the Chinese Academy of Sciences, said on Saturday.
"Current physical laws cannot describe well the substances in the state of a pulsar, since no lab on Earth can create a density as high as a pulsar. So we have to conduct more observations of pulsars," Zhang says. Lu Fangjun, chief designer of the payload of HXMT, says long-time monitoring of pulsars could help unravel the mystery of their energy sources.
A pulsar is so strange that when the first one was discovered, it was mistaken for signals from aliens. There are still many mysteries about this kind of star. It is found to be a highly magnetised, rotating neutron star, which emits two beams of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing towards the earth. It is much the same as how a lighthouse can be seen only when the light is pointed at an observer.
A neutron star is the collapsed core of a large star. Neutron stars are the smallest and densest stars known to exist. Though they typically have a radius of 10 km, they can have a mass about twice that of the Sun. A neutron star is so dense that one teaspoon of its material would have the mass of a mountain over 3,000 metres high, or about 900 times the mass of the Great Pyramid of Giza.
British astronomers Jocelyn Bell Burnell and Antony Hewish discovered the first pulsar in 1967. They nicknamed the strange signal LGM-1, for "little green men". It was not until a second pulsating source was found in a different part of the sky that the "LGM hypothesis" was abandoned. Scientists have discovered over 2,000 pulsars so far. The Milky Way is thought to have around 100 million of them, a figure obtained by estimating the number of stars that have undergone supernova explosions.
With their super strong gravitational and electromagnetic fields and high density, pulsars are regarded as natural laboratories of extreme physical conditions.