Green Bank Telescope

The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, [1] surpassing the Effelsberg 100-m Radio Telescope in Germany. [2] The Green Bank site was part of the National Radio Astronomy Observatory (NRAO) until September 30, 2016. Since October 1, 2016, the telescope has been operated by the independent Green Bank Observatory.[3] The telescope's name honors the late Senator Robert C. Byrd who represented West Virginia and who pushed the funding of the telescope through Congress.

Green Bank Telescope
The Green Bank Telescope
Alternative namesGBT 
Named afterRobert Byrd 
Part ofGreen Bank Observatory
National Radio Astronomy Observatory 
Location(s)Green Bank, United States National Radio Quiet Zone, Pocahontas County, US
Coordinates38°25′59″N 79°50′23″W
OrganizationGreen Bank Observatory
National Radio Astronomy Observatory 
Observatory code 256 
Observing time365 nights per year 
Built1990–2000
First light23 August 2000 
Telescope styleGregorian telescope
radio telescope 
Diameter100 m (328 ft 1 in)
Collecting area2.34 acres (102,000 sq ft)
Focal length60 m (196 ft 10 in)
Websitegreenbankobservatory.org/science/telescopes/gbt/
Location of Green Bank Telescope
Related media on Wikimedia Commons

The Green Bank Telescope operates at meter to millimeter wavelengths. Its 100-meter diameter collecting area, unblocked aperture, and good surface accuracy provide superb sensitivity across the telescope's full 0.1–116 GHz operating range. The GBT is fully steerable, and 85 percent of the local celestial hemisphere is accessible. It is used for astronomy about 6500 hours every year, with 2000–3000 hours per year going to high-frequency science. Part of the scientific strength of the GBT is its flexibility and ease of use, allowing for rapid response to new scientific ideas. It is scheduled dynamically to match project needs to the available weather. The GBT is also readily reconfigured with new and experimental hardware. The high-sensitivity mapping capability of the GBT makes it a vital complement to the Atacama Large Millimeter Array, the Expanded Very Large Array, the Very Long Baseline Array, and other high-angular resolution interferometers. Facilities of the Green Bank Observatory are also used for other scientific research, for many programs in education and public outreach, and for training students and teachers.

The telescope began regular science operations in 2001, making it one of the newest astronomical facilities of the US National Science Foundation (NSF). It was constructed following the collapse of a previous telescope at Green Bank, a 90.44 m paraboloid that began observations in October 1961.[4] The previous telescope collapsed on 15 November 1988 due to the sudden loss of a gusset plate in the box girder assembly, which was a key component for the structural integrity of the telescope.[5][6]

Location
The Robert C. Byrd Green Bank Radio Telescope (GBT) has a collecting area of 2.3 acres (0.93 ha) which focuses the radio waves falling on it onto sensitive receivers at the top of the boom attached to the side.

The telescope sits near the heart of the United States National Radio Quiet Zone, a unique area located in the town of Green Bank, West Virginia, where authorities limit all radio transmissions to avoid emissions toward the GBT and the Sugar Grove Station. The location of the telescope within the Radio Quiet Zone allows for the detection of faint radio-frequency signals which man-made signals might otherwise mask. The observatory borders National Forest land, and the Allegheny Mountains shield it from some radio interference.

The telescope's location has been the site of important radio astronomy telescopes since 1957.[7] It currently houses seven additional telescopes, and in spite of its somewhat remote location, receives about 40,000 visitors each year.[8]

Description

The structure weighs 7,600 metric tons (8,400 short tons) and is 485-foot (148 m) tall. The surface area of the GBT is a 100 by 110 meter active surface with 2,209 actuators (small motors used to adjust the position) for the 2,004 surface panels, making the total collecting area of 2.3 acres (9,300 m2).[9][10] The panels are made from aluminium manufactured to a surface accuracy of better than 50 micrometres (0.0020 in) RMS.[11] The actuators adjust the panel positions to compensate for sagging, or bending under its own weight, which changes as the telescope moves. Without this so-called "active surface", observations at frequencies above 4 GHz would not be as efficient.[12]

Unusually for a radio telescope, the primary reflector is an off-axis segment of a paraboloid. This is the same design used in familiar home satellite television (e.g., DirecTV) dishes. The asymmetric reflector allows the telescope's focal point and feed horn to be located at the side of the dish, so that it and its retractable support boom do not obstruct the incoming radio waves, as occurs in conventional radio telescope designs with the feed located on the telescope's beam axis.

The offset support arm houses a retractable prime focus feed horn in front of the 8 m subreflector and eight higher-frequency feeds on a rotating turret at the Gregorian focus. Operational frequencies range from 290 MHz to 100 GHz.[12]

Because of its height (at 148 meters or 485 feet tall, it is 60% taller than the Statue of Liberty) and bulk (16 million pounds), locals sometimes refer to the GBT as the “Great Big Thing”.[13][14]

Discoveries
Composite image of a spectral line observation of star forming region W51, showing the distribution of ammonia in the region. The image of the telescope from a time lapse film of a night of observations

In 2002, astronomers detected three new millisecond pulsars in the globular cluster Messier 62.[15]

In 2006, several discoveries were announced, including a large coil-shaped magnetic field in the Orion molecular cloud,[16] and a large hydrogen gas superbubble 23,000 light years away, named the Ophiuchus Superbubble.[17][18]

Since 2006, numerous discoveries have been made, including the most massive neutron star detected so far,[19] a cloud of primordial gas which surrounds other galaxies, vast molecular clouds surrounding other galaxies, and complex molecules, such as sugar, in space.

Funding threatened

In response to limited budgetary issues, the Division of Astronomical Sciences (AST) of the National Science Foundation (NSF) commissioned a portfolio review committee, which conducted its work between September 2011 and August 2012.[20][21][22] The committee, which reviewed all AST-supported facilities and activities, was composed of 17 external scientists and chaired by Daniel Eisenstein of Harvard University.[20][21][22][23] As part of the committee's August 2012 recommendation for the closure of six facilities, was that the Robert C. Byrd Green Bank Telescope (GBT) should be defunded over a five-year period.[22][23][24]

In July 2014, the United States Senate Committee on Appropriations approved the NSF's fiscal year 2014 budget, which did not call for divestment of the GBT in that fiscal year. The facility then began looking for partners to help fund its $10 million annual operating costs.[25]

On October 1, 2016, the National Radio Astronomy Observatory at Green Bank separated from the NSF and began accepting funding from private sources to stay operational as an independent institution, the Green Bank Observatory.[26]

Relation to Breakthrough Listen

The telescope is a key facility of the Breakthrough Listen project,[27] in which it is used to scan for radio signals possibly emitted by extraterrestrial technologies. In late 2017, the telescope was used to scan ʻOumuamua for signs of extra terrestrial intelligence.[28][29]

See also

References
  1. Benningfield, Damond (June 2016). "SETI Gets an Upgrade". Air & Space/Smithsonian. National Air and Space Museum. Retrieved May 27, 2016.
  2. https://www.mpifr-bonn.mpg.de/en/effelsberg
  3. "NRAO Structural Changes: Announcing the Separation of the Green Bank Observatory and the Long Baseline Observatory, Associated Universities, Inc".
  4. Burner Flegel, Louise (April 14, 2016). "National Radio Astronomy Observatory". e-WV: The West Virginia Encyclopedia. Retrieved January 1, 2020.
  5. NRAO 300 foot Telescope Collapse
  6. "Decision Announced in Green Bank Telescope Arbitration Case" (Press release). National Radio Astronomy Observatory. February 12, 2001. Bibcode:2001nrao.pres....5. Retrieved January 1, 2020. ...with work to begin on December 19, 1990... telescope was accepted from the contractor on October 13, 2000, nearly six years later than the original contract delivery date.
  7. Lockman, F. J.; Ghigo, F. D.; Balser, D. S., eds. (2007). But it was Fun: The first forty years of radio astronomy at Green Bank (PDF). Green Bank, W. Va.: National Radio Astronomy Observatory. ISBN 978-0-97004-112-8. OCLC 144734774. Retrieved January 1, 2020.
  8. "Green Bank Facts". greenbankobservatory.org. Green Bank Observatory. Retrieved 2017-10-31.
  9. "Robert C. Byrd Green Bank Telescope". www.gb.nrao.edu. National Radio Astronomy Observatory. 9 August 2011. Archived from the original on 9 August 2011.
  10. Frayer, David. "Proposing for the GBT". The National Radio Astronomy Observatory. Retrieved 1 November 2016.
  11. Hunter, Todd R.; et al. (2011). "Holographic Measurement and Improvement of the Green Bank Telescope Surface". Publications of the Astronomical Society of the Pacific. 123 (907): 1087–1099. arXiv:1107.2081. Bibcode:2011PASP..123.1087H. doi:10.1086/661950.
  12. "The Proposer's Guide for the Green Bank Telescope" (PDF). National Radio Astronomy Observatory.
  13. Jim Merithew, “Silence! The Last of the Giant Radio Telescopes Is Listening to the Universe”, Wired (October 2009)
  14. John M Thompson, “W.Va. Observatory Scans the Universe for Radio Signals”, The Washington Post (19 November 2008)
  15. "Newly Commissioned Green Bank Telescope Bags New Pulsars" (Press release). National Radio Astronomy Observatory. 2002-01-04.
  16. Green Bank Telescope scores big finds in space: Fastest pulsar Slinky magnetics superbubble of hydrogen ID, The Charleston Gazette, 2006-01-17
  17. Pidopryhora, Yurii; Lockman, Felix J; Shields, Joseph C (2007). "The Ophiuchus Superbubble: A Gigantic Eruption from the Inner Disk of the Milky Way". The Astrophysical Journal. 656 (2): 928–942. arXiv:astro-ph/0610894. Bibcode:2007ApJ...656..928P. doi:10.1086/510521.
  18. "Huge 'Superbubble' of Gas Blowing Out of Milky Way". PhysOrg.com. 2006-01-13. Retrieved 2008-07-04.
  19. Green Bank Observatory (16 September 2019). "Most massive neutron star ever detected, almost too massive to exist". ScienceDaily. ScienceDaily. Retrieved 26 September 2019.
  20. "AST Portfolio Review". www.nsf.gov. Retrieved March 13, 2020.
  21. "AST Portfolio Review Webinar" (PDF). www.nsf.gov. October 23, 2012. Retrieved March 13, 2020.
  22. Bhattacharjee, Yudhijit (August 17, 2012). "Major U.S. Telescopes Face Funding Ax". Science. ISSN 1095-9203. OCLC 716906842. Retrieved March 13, 2020.
  23. Lavender, Gemma (August 22, 2012). "US telescopes faced with closure". Physics World. Bristol, England: IOP Publishing. ISSN 2058-7058. OCLC 37217498. Retrieved March 13, 2020.
  24. Hand, Eric (August 21, 2012). "US telescopes face up to agency cuts". Nature (published August 23, 2012). 488 (7412): 440. Bibcode:2012Natur.488..440H. doi:10.1038/488440a. PMID 22914143. Retrieved March 13, 2020.
  25. Bumgardner, Bryan (September 4, 2013). "Too Big to Fail? The Green Bank Telescope's Uncertain Future". Scientific American. Springer Nature. ISSN 0036-8733. Retrieved January 1, 2020.
  26. Scoles, Sarah (October 7, 2016). "What Happens When a Space Observatory Goes Rogue". Wired. Condé Nast. ISSN 1078-3148. OCLC 24479723. Retrieved January 1, 2020.
  27. "A Russian Tycoon is Spending $100 Million to Hunt for Aliens".
  28. "'Oumuamua Probably Isn't a Spaceship—But It Could Have Passengers". WIRED. Retrieved 2018-01-01.
  29. Enriquez, E.; Siemion, A.; Lazio, J.; Lebofsky, M.; MacMahon, D.; Park, R.; Croft, S.; DeBoer, D.; Gizani, N.; Gajjar, V.; Hellbourg, G.; Isaacson, H.; Price, D. (2018). "Breakthrough Listen Observations of 1I/'Oumuamua with the GBT". Research Notes of the American Astronomical Society. 2 (1). arXiv:1801.02814. Bibcode:2018RNAAS...2a...9E. doi:10.3847/2515-5172/aaa6c9.
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