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"China's Sky Eye" FAST has made new major discoveries and has also appeared on the cover of the latest issue of Nature.
This time, an international team led by the National Astronomical Observatory Kyodo-chong and Li Song used FAST to measure the magnetic field inside the 450-light-year alien nebula.
Their observations could upend scientists' theories of star formation, perhaps 10 times faster than we think.
△ FAST detects molecular cloud magnetic fields, picture from the National Astronomical Observatory
The National Astronomical Observatory of the Chinese Academy of Sciences said at a press conference that this is a breakthrough from 0 to 1 in the use of atomic radiation to detect the magnetic field of molecular clouds.
Professor Paola Caselli of the Max Planck Institute for Astrophysics said: "If this is also the case in other gas clouds, then [this discovery] will be revolutionary for the field of star formation research. ”
△ FAST (500-meter aperture spherical radio telescope), image from Xinhua News Agency
FAST found something
It has long been believed that astronomers have long believed that star formation takes millions of years. In the process of nebula collapse into stars, the magnetic field plays a key role.
Faraday measures the magnetic field with its own coils, but it is obviously impossible for us to extend the antenna into outer space. Fortunately, the Zeyman effect allows us to measure magnetic fields indirectly.
The so-called "Zeyman effect" refers to the phenomenon that a line of the spectrum splits into multiple lines under the action of a magnetic field, and the strength of the magnetic field can be calculated by measuring the frequency difference between multiple lines.
△ Example of the Zeyman effect: A is the spectrum without a magnetic field, and B and C are the spectrum when there is a magnetic field
For nebulae, the Zeyman effect occurs mainly in the radio band, and FAST is the world's most sensitive radio telescope.
But the Zeyman effect in nebulae is too weak.
In 2003, Li and Paul Goldsmith proposed a narrow self-absorption (HINSA) technique to solve this problem.
HINSA is a radio signal produced by the collision of hydrogen atoms with hydrogen molecules to cool. HINSA also reacts relatively strongly to magnetic fields, 5 to 10 times stronger than the general molecular signal.
Therefore, the Zeyman effect of HINSA is considered a powerful tool for studying magnetic fields in nebulae.
Previously, scientists studied the 450-light-year-old L1544 molecular cloud with other radio telescopes, measuring the magnetic field strength of its outer layer and core, respectively.
△ L1544 molecular cloud, image from ESA
They found that in the outer layer, magnetic forces dominate, while the core, although magnetic, is stronger, but the molecular density is also greater, so universal gravity dominates.
What is missing is data from the middle layer between the outer layer and the core, and FAST has taken on the task of measuring the magnetic field in this area, for the first time to detect the HINSA Zehmann effect.
As a result, the National Astronomical Observatory team found that the magnetic field strength of the middle layer is 4 micro gauss, only one-hundredth of the Earth's magnetic field, and it is not stronger than the outer layer of the molecular cloud.
"If you want to resist the gravitational pull of a 100-fold increase in density, the magnetic field needs to be stronger, but that doesn't happen," Li said.
That is, the magnetic forces in the nebula should be closer to the outer layer than the core, and it will take much less time for the nebula to collapse into a star than previously predicted.
Qing Daochong, the paper's first author, said the discovery meant that gas clouds evolved into stellar embryos 10 times faster than previously thought.
How the interstellar magnetic field dissipated causing the nebula to collapse remains an unsolved mystery in star formation.
For a long time, astronomers believed that it was mainly bipolar diffusion that separated neutral particles from the plasma, resulting in gravitational collapse.
The latest findings suggest that magnetic field dissipation occurs during the formation of molecular cloud surfaces, where there may be mechanisms different from bipolar diffusion.
FAST has made a new contribution
Just a day before FAST's new discovery appeared on the cover of Nature, the National Astronomical Observatories of the Chinese Academy of Sciences held a press conference to introduce the important scientific achievements made by FAST in the frontier field of international astronomy last year.
△ The scene of the press conference of the National Astronomical Observatory, the picture is from Xinhua News Agency
In addition to neutral hydrogen line measurements of interstellar magnetic fields, FAST made the following significant discoveries:
1. Detected 1652 outbreak events in about 50 days, obtaining the largest sample of rapid radio burst (FRB) events to date, exceeding the total number of outbreak events published in all previous articles in the field, and the research paper was published in Nature on October 14 last year.
2. As of now, FAST has found about 500 pulsars, becoming the most efficient device in the world.
The National Astronomical Observatory said that in 2021, based on the obvious advantages of ultra-high sensitivity, FAST has become a sharp tool for viewing the sky in the field of medium and low frequency radio astronomy.
FAST has been a major force in the search for pulsars in the past. The new findings suggest that FAST can also be involved in astronomical problems, including star formation.
Chang Jin, an academician of the Chinese Academy of Sciences and director of the National Astronomical Observatory, said that in the future, FAST will be committed to finding sub-millisecond pulsars with less than 1 millisecond, which is also a system that the world is looking for.
In addition, FAST also plans to open 1% of the observation time to primary and secondary school students across the country in 2022, with primary and secondary school students proposing scientific ideas and astronomers helping them realize them.
Team Profile
The first author of this article is Qing Daochong from Tsinghua University in Taiwan, who was recruited to work at the National Astronomical Observatory in 2017.
△ Qing DaoChong, picture from the ETtoday website
When he graduated, he submitted resumes in Taiwan and the mainland, but in the end he only received a reply from the National Astronomical Observatory.
Qing Daochong is very excited to work in Tianyan because it is a "dream job" for him.
The corresponding author of this article is Li Ming, chief scientist of FAST of the National Astronomical Observatory. He studied at Peking University as an undergraduate and later pursued his Ph.D. at Cornell University in the United States. After graduation, he worked at the Smithsonian Center for Astrophysics and NASA's Jet Propulsion Laboratory.
△ Li Ling gave a speech in "Let's Talk", picture from CCTV
In 2012, Li Returned to China and entered the National Astronomical Observatory of the Chinese Academy of Sciences, serving as deputy chief engineer of FAST Engineering in 2015 and chief scientist of FAST in 2018.