By Yu Fei, Li Mengxin and Qi Jian
BEIJING, Oct. 16 (Xinhua) -- One is rapid and strong, and the other is slow and weak, like the heartbeats of a youth and an old man passing through a distance of thousands of light years, and then heard by the most sensitive "ear" on Earth.
The "ear" is the Five-hundred-meter Aperture Spherical Telescope (FAST), the world's largest radio telescope, with a dish as large as 30 football fields. It is located in a valley deep in southwest China's mountainous Guizhou Province.
During the debugging and trial of the telescope since its completion in September 2016, FAST has detected dozens of pulsar candidates, six of them confirmed by telescopes in other countries. Chinese scientists produced a sound effect of the first two confirmed pulsars based on the observed signals, enabling ordinary people to hear the "heartbeats" deep in the universe.
The objectives of FAST include searching for pulsars, neutral hydrogen, interstellar molecules and signals from the extraterrestrial life.
"Looking for aliens is one of the goals of FAST. But we haven't started that kind of search during the debugging and trial period," said Li Di, chief scientist of the Radio Astronomy Division of the National Astronomical Observatories (NAO) under the Chinese Academy of Sciences (CAS).
However, the pulsars discovered by FAST are an enigma enough. When the first pulsar was discovered in 1967, it was mistaken for a signal from aliens.
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. 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.
"There are many strange phenomena and natures of pulsars that we don't understand," said Chen Xuelei, a researcher with NAO, adding that scientists have discovered some millisecond pulsars spinning very fast. "More study is needed to find out why they rotate so fast."
With their super strong gravitational and electromagnetic fields and high density, pulsars are regarded as natural laboratories of extreme physical conditions, Chen said.
"If we could find a binary star system composed of a pulsar and a black hole, we would be able to study the space-time around the black hole by using the pulsar," Chen said.
Pulsars can help scientists study gravitational waves. FAST will help improve the chances of detecting low frequency gravitational waves, said Wu Xiangping, a CAS academician, predicting great breakthroughs in this area in the years ahead.
Pulsars 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.
The first two confirmed pulsars discovered by FAST were detected on the nights of Aug. 22 and 25 respectively. But Li couldn't recall the scene exactly as FAST has already found dozens of pulsar candidates thanks to its high sensitivity.
"As a matter of fact, we can detect high-quality pulsar candidates almost every night," said Li.
When the first pulsar was discovered half a century ago, China was still struggling in poverty and turmoil. As a result, none of the previous more than 2,700 discoveries of pulsars was made by China.
But now, as China builds a well-off society, it has the capability to explore the strange and mysterious celestial bodies, and endeavor to answer those ultimate questions: How was the universe created? Where did we come from? Are we lonely in the universe?
For Chinese astronomers to lead in global astronomy, they must have advanced astronomical instruments. The completion of FAST, the largest astronomical construction in Chinese history, cost about 1.2 billion yuan (182 million U.S. dollars), more than 20 years and tremendous efforts of the scientists and engineers.
Now, China is in the pulsar-searching club.
Li predicted that after it starts formal operation in 2019, FAST will be able to find over a hundred pulsars per year. The telescope is expected to discover twice the number of pulsars currently known.
It is also expected to find 50 to 80 pulsars in M31, the nearest major galaxy to the Milky Way. It is the only radio telescope in the world with this capability.
A NEW ERA
Li, who did research at the California Institute of Technology and NASA in the United States, returned to China in 2012 for the construction of FAST. In the remote valley in Guizhou, he lived in the barrack-like housing without even a bathroom for several years.
"Scientific research is the process of seeking truth. Like detective work, painting or building furniture, you might encounter many obstacles on the way, but you will also see gradual progress, and finally get something that is incredibly important or beautiful. The more bitter the hardship, the sweeter the happiness," said Li.
This year is momentous for China' s astronomical community. On June 15, China' s space telescope, the Hard X-ray Modulation Telescope (HXMT), was launched to detect black holes and pulsars. The initiator of the satellite is Li Di's father Li Tipei, a renowned astrophysicist and academician of the CAS.
"In modern history, China has lagged behind in the world, and it is the hope of our generation to put China at the forefront of the global natural science community," said Li Tipei.
Li Di said FAST takes in the past and brings about the future. "The era of systematic pulsar research with Chinese telescope has just started. We hope to make the telescope an important scientific instrument of mankind."
A multi-beam receiver will be installed on FAST to survey space with multiple scientific objectives. That means it can obtain data on pulsars, celestial spectrums and fast radio bursts in one scan. Through this original technique, scientists will be able to find more than 1,000 pulsars, over 100,000 galaxies and dozens of fast radio bursts.
"We will rely on self-innovative equipment and advanced observation methods to make systematic scientific discoveries." Li said. "It will be the dawn of a new era."
"For human beings, exploring the unknown and satisfying curiosity is an equally essential right as eating and sleeping. Exploration of the unknown will inspire human creativity, enabling us to make unprecedented achievements and find imaginative solutions, which is extremely valuable."