The observatory built on the karst landform has repeatedly "seen" the secrets of astronomy

Author | Wang Qing

Audit | Ding Yi

Editor | Zhao Jingyuan

Arecibo Observatory at night. Image credit: University of Central Florida

Arecibo Observatory is located in a valley about 20 kilometers south of Arecibo, Puerto Rico, a U.S. overseas territory. It is famous for its world-famous single-aperture spherical radio telescope, which was once the largest in the world. This observatory is not only an important base for astronomical research, but also a milestone in human exploration of the universe.

The terrain near the Arecibo Observatory is unique, with naturally formed karst landforms, providing an ideal site for the construction of a large radio telescope. The construction of the observatory began in 1960 and was completed in 1963, marking an important step forward in the field of radio astronomy.

Arecibo radio telescope. Image credit: Florida Space Institute

The main facility of the Arecibo Observatory is a 305-meter diameter spherical radio telescope, commonly referred to as the Arecibo radio telescope. In addition, there is a smaller radio telescope (12 meters in diameter), a lidar facility and a visitor center. Before the completion of my country's 500-meter Aperture Spherical Radio Telescope (FAST) in 2016, the Arecibo radio telescope was the world's largest single-aperture spherical radio telescope [it is worth noting that the Russian Academy of Sciences Radio Telescope-600 (RATAN-600), built in 1974, has a larger aperture of 576 meters, but its reflecting surface is not a complete sphere, but a ring structure].

The Arecibo radio telescope's huge metal structure uses a spherical reflector made of perforated aluminum panels to focus incoming radio waves on a movable antenna structure about 168 meters from the reflector surface. Although the telescope is fixed and cannot rotate, by changing the position of the antenna feed, it can scan a strip of the sky for in-depth radio astronomy observations.

Size comparison of the Arecibo radio telescope (top), the 500-meter Aperture Spherical radio telescope (middle), and the Russian Academy of Sciences Radio Telescope-600 (bottom). Image source: Wikipedia

Over more than half a century, the Arecibo radio telescope has achieved many brilliant achievements, and here are just a few to name a few.

1. In 1967, a team led by American astronomer Gordon Pettengill used it to measure Mercury's rotation period to be 59 days, rather than the previously believed 88 days.

2. In 1974, American astronomers Russell Hulse and Joseph Taylor used it to discover the first pulsar binary system (that is, a binary star system containing a pulsar) - PSR B1913+16. They observed the system for a long time and found that the orbital period of this binary star system was slowly accelerating. This was indirect evidence of gravitational wave radiation, verifying an important prediction of Einstein's general theory of relativity. The two were awarded the 1993 Nobel Prize in Physics.

3. In 1974, the Arecibo radio telescope sent the "Arecibo Message" containing basic information about the Earth and humanity to the Hercules globular cluster M13.

Arecibo information. Image source: Planetary Habitability Laboratory, translated by Zhao Jingyuan

4. In 1992, Polish astronomer Aleksander Wolszczan and Canadian astronomer Dale Frail discovered two planets orbiting the pulsar PSR B1257+12 using the Arecibo radio telescope [In 1994, Wolszczan discovered a third planet orbiting the pulsar]. This was the first extrasolar planetary system discovered by humans.

In addition, the Arecibo radio telescope has also performed radio imaging of some near-Earth asteroids and discovered many binary asteroid systems, making important contributions to planetary defense. It has also participated in the Search for Extraterrestrial Intelligence (SETI) program and provided data sources for the distributed computing project SETI@home, but no evidence of the existence of extraterrestrial civilizations has been found in it. The Arecibo radio telescope has made great achievements in many fields of astronomy and has become an immortal monument in the human exploration of the universe.

Important discoveries made by the Arecibo radio telescope. Image source: Future, Chinese translation: Zhao Jingyuan

Arecibo Observatory is not only a holy place for astronomical research, but also an important place for scientific education and public science popularization. Its visitor center opened in 1997 and features interactive exhibits on radio telescopes, astronomy and atmospheric science. It attracts astronomers, students and tourists from all over the world to visit and learn. Through observation and experiments, people can gain a deeper understanding of the mysteries of the universe and stimulate their interest and love for science.

Unfortunately, however, the Arecibo radio telescope suffered serious damage in 2020. In August of that year, a steel cable supporting the platform above the telescope broke, leaving a crack about 30 meters long on the telescope's reflecting surface and damaging the feed cabin. In November of the same year, after another steel cable broke, the National Science Foundation announced that the Arecibo radio telescope was in danger of collapse and could not be safely repaired and would be dismantled. On December 1 of the same year, the central platform collapsed onto the reflecting surface of the radio telescope, completely damaging it and ending its nearly 60-year mission of space exploration.

The collapsed Arecibo radio telescope. Image source: Reference 10

The Arecibo Observatory is a landmark scientific facility. Its brilliant achievements and tragic ending will become an important chapter in the human exploration of the mysteries of the universe. Although the Arecibo telescope has collapsed, its legacy and influence in the field of astronomy are far-reaching. In order to commemorate this great scientific facility, the National Science Foundation plans to build an education center on the site of the Arecibo Observatory to continue to inherit and carry forward the spirit and knowledge of astronomy.

At the same time, the collapse of the Arecibo radio telescope also reminds us that the construction and maintenance of scientific facilities require long-term investment and attention. In the future, with the advancement of science and technology and the deepening of human exploration of the universe, we look forward to building more advanced and more stable radio telescopes and other scientific facilities to reveal more mysteries of the universe to mankind.

References

1. The equipment platform of Arecibo Telescope collapsed, Chinese Science, 2021, (19): 11

2. The most accurate clock in the universe: the discovery of millisecond pulsars, China Metrology, 2016, (11): 52

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10. Elizabeth Howell, These photos of the Arecibo Observatory telescope collapse are just heartbreaking, space.com, https://www.space.com/arecibo-observatory-radio-telescope-collapse-photos

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13. Vicky Stein, Arecibo Observatory: The rise, legacy, and tragic collapse of a giant, space, https://www.space.com/20984-arecibo-observatory.html

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