China recently unveiled FAST, the world's largest single-dish radio telescope.
The Chinese Academy of Sciences announced this week that its new Five hundred meter Aperture Spherical Telescope (FAST) is now ready to scan the skies. With a dish 500 m across, this behemoth is now the largest filled-in, single-dish radio telescope in the world. With an area equal to 30 soccer fields, a Nimitz-class aircraft carrier could easily float in the 500 meter dish from bow to stern, with room to spare.
Only the 576-m diameter of Russia's RATAN-600 system is physically larger than FAST, though its collecting surface is a large ring rather than a dish. It's not all about size though — RATAN-600 actually only has an effective collecting area of 12,000 m2. FAST's effective collecting area is 70,000 m2. The 305-m-wide Arecibo Observatory in Puerto Rico, which formerly held the title of largest single dish radio telescope in the world, has an effective collecting area of about 31,000 m2.
Taking the FAST Track in Radio Astronomy
FAST is located in southwestern China in the sparsely populated Guizhou Province. Like Arecibo, the radio telescope was built inside a natural depression in the limestone-dominated terrain, and it uses mountainous karst features surrounding the observatory to block out radio interference.
In order to create a zone free of radio interference, China also relocated 9,110 people from villages in the surrounding area while building the telescope.
First proposed in 1994, the project was green-lighted by the Chinese government in 2007, and groundbreaking followed the next year. Formal construction began in 2011. The last of the instrument's 4,450 reflecting panels was finally put into position earlier this year on July 3rd.
FAST will probe the universe at radio wavelengths, hunting for faint pulsars, mapping neutral hydrogen in distant galaxies, and searching for signs of extraterrestrial communications and intelligence.
“Once completed, FAST will lead the world for at least 10 to 20 years,” says director general and telescope designer Yan Jun (National Astronomical Observatories of China) in a recent press release.
FAST's expected resolution is 2.9 arcminutes, which is pretty good for single-dish radio astronomy. Although its surface is spherical overall, FAST uses actuators to push and pull on the corners of a 300-m-wide subset of the individual panels to attain a near-paraboloidal shape to achieve this focus.
The radio telescope now enters an extensive commissioning phase. FAST made its first observation of a pulsar 1,351 light-years away this past month.
FAST will also use the Next Generation Archive System (NGAS) developed by the International Center for Radio Astronomy (ICRAR) in Perth, Australia, and the European Southern Observatory to store and maintain the large amount of data it's expected to collect. NGAS expects to handle about 3 petabytes (3 × 1015 bytes) of data from FAST every year, enough to fill 120,000 single-layer, 25-gigabyte Blu-ray disks.
“This system is already being used by a whole suite of observatories around the world,” says Andreas Wicenec (University of Western Australia). “During the last few years the software has been significantly upgraded to support very large data streams like the ones coming out of SKA precursors.”
As with Arecibo, FAST's receivers, suspended high above the dish, are only partially steerable. Located at latitude 26°N, the radio telescope points straight overhead, allowing Earth's rotation to "point" the dish as the sky sweeps past. FAST's significantly deeper dish lends it a wider field of view than Arecibo's, though. It can cover a swath of sky within 40° of its zenith — Arecibo is limited to 20° from its zenith.
However, FAST uses a smaller receiver platform than Arecibo and does not house the large radar transmitters needed to ping large near Earth asteroids as part of planetary defense.
Big Radio Dishes: Past, Present & Future
FAST carries on the tradition of large radio telescope construction that started shortly after the Second World War. The 76.2-m Lovell Telescope at Jodrell Bank outside of Manchester, England, was completed in 1957. It was surpassed first by Green Bank in West Virginia, and later by the 100-m Effelsberg radio telescope in Germany. Since 1963, Arecibo has held the title of largest single-filled dish radio telescope until this year.
Perhaps, like the 40-inch Yerkes refractor, FAST's record-setting dimensions will never be exceeded. Future radio observatories such as the Square Kilometer Array will be "dish farms," like the Very Large Array in New Mexico, using the interference between the radio signal collected by many dishes to assemble high-resolution images.
FAST is set to usher in a new generation of radio astronomy, with more exciting science to come. Learn more about it at the facility's website.