BEIJING -- Chinese scientists have discovered six new pulsar stars in the Milky Way, by using the Five-hundred-meter Aperture Spherical Telescope (FAST), the world's largest radio telescope.

One of the pulsars is estimated to be 16,000 light years away, rotating at a speed of 1.83 seconds, while another is thought to be about 4,100 light years away, spinning at 0.59 of a second.

Pulsars are so strange that when the first one was discovered, it was mistaken for a signal from aliens. They are still an enigma.

A pulsar is 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 at Earth, in much the same way as 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. They typically have a radius of 10 km, but 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 on Nov. 28, 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 now identified more than 2,000 pulsars.

The Milky Way is thought to have around 100 million of them, based on an estimate of 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 laboratory. 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.