China will soon launch a space telescope, the Hard X-ray Modulation Telescope (HXMT), to observe pulsars in the galaxy of Milky Way, according to Chinese scientists.
"We are still not clear about the interior of pulsars," says Zhang Shuangnan, lead scientist of HXMT and director of the Key Laboratory of Particle Astrophysics of the Chinese Academy of Sciences.
"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.
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 magnetized, rotating neutron star, which emits two beams of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward 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 meters high on Earth, or about 900 times the mass of the Great Pyramid of Giza. Most of the basic models for these objects imply that they are composed almost entirely of neutrons.
Neutron stars have very precise intervals between pulses that range from milliseconds to seconds. They are regarded as the most accurate astronomical clock in the universe. Scientists believe they can use pulsars as "lighthouses" to help navigation in future interplanetary or interstellar travel.
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.
To date, scientists have discovered more than 2,000 pulsars. 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.
For instance, the magnetic field on the surface of a neutron star is at least a million times that created in the most advanced lab. In addition, neutron stars might be particle accelerators with the highest energy in the known universe. Scientists could study many phenomena that they cannot replicate on Earth by observing neutron stars, 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.
Scientists still don't fully understand how the pulses of neutron stars and the strong magnetic fields around them are formed. China's new space telescope might yield some clues, says Song Liming, deputy chief designer of the ground application system of HXMT.