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Event Horizon Telescope

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Event Horizon Telescope
File:Event horizon telescope logo 2019.png
Alternative namesEHT Edit this on Wikidata
Websiteeventhorizontelescope.org Edit this at Wikidata
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Soft X-ray image of Sgr A* (center) and two light echoes from a recent explosion (circled).

The Event Horizon Telescope (EHT) is a large telescope array consisting of a global network of radio telescopes and combining data from several very-long-baseline interferometry (VLBI) stations around the Earth. The aim of the EHT project is to observe the immediate environment of supermassive black holes, e .g., Sagittarius A* at the center of the Milky Way as well as the even larger black hole in the center of the supergiant elliptical galaxy Messier 87, with angular resolution, about 25 micro-arcseconds, comparable to the black hole's event horizon.[1][2]

The first image of a black hole, the supermassive one at the center of galaxy Messier 87, was published by the EHT Collaboration on April 10, 2019.[3] The black hole was given the nickname Pōwehi, meaning "embellished dark source of unending creation" in Hawaiian.[4]

Overview

The EHT is composed of many radio observatories or radio telescope facilities around the world to produce a high-sensitivity, high-angular-resolution telescope. Through the technique of very-long-baseline interferometry (VLBI), many independent radio antennas separated by hundreds or thousands of miles can be used in concert to create a virtual telescope with an effective diameter of the entire planet.[5] The effort includes development and deployment of submillimeter dual polarization receivers, highly stable frequency standards to enable very-long-baseline interferometry at 230–450 GHz, higher-bandwidth VLBI backends and recorders, as well as commissioning of new submillimeter VLBI sites.[6]

Each year since its first data capture in 2006, the EHT array has moved to add more observatories to its global network of radio telescopes. The first image of the Milky Way's supermassive black hole, Sagittarius A*, was expected to be produced in April 2017,[7][8] but because the South Pole Telescope is closed during winter (April to October), the data shipment delayed the processing to December 2017 when the shipment arrived.[9]

Data collected on hard drives are transported by airplane (a so-called sneakernet) from the various telescopes to the MIT Haystack Observatory near Boston, Massachusetts; and to the Max Planck Institute for Radio Astronomy, Bonn, Germany, where the data are cross-correlated and analyzed on a grid computer made from about 800 CPUs all connected through a 40 Gbit/s network.[10]

Scientific results

First image of the event horizon of a black hole (M87*) captured by the Event Horizon Telescope.[11][1][12]

The Event Horizon Telescope Collaboration announced its first results in simultaneous press conferences worldwide on April 10, 2019.[13] The announcement featured the first direct image of a black hole, which showed the supermassive black hole at the center of Messier 87, provisionally designated M87*.[1] The scientific results were presented in a series of six papers published in The Astrophysical Journal Letters.[14]

The image provided a test for Albert Einstein's general theory of relativity under extreme conditions.[5][8] Studies have previously tested general relativity by looking at the motions of stars and gas clouds near the edge of a black hole. However, an image of a black hole brings observations even closer to the event horizon.[15] Relativity predicts a dark shadow-like region, caused by gravitational bending and capture of light, which matches the observed image. The published paper states: "Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity."[16] Paul T.P. Ho, EHT Board member, said: "Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter, and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well."[14]

The image also provided new measurements for the mass and diameter of M87*. EHT measured the black hole's mass to be approximately 6.5 billion solar masses and measured the diameter of its event horizon to be approximately 40 billion kilometres (270 AU; 0.0013 pc; 0.0042 ly), roughly 2.5 times smaller than the shadow that it casts, seen at the center of the image.[14][15] From the asymmetry in the ring, EHT inferred that the matter on the brighter south side of the disk is moving towards Earth, the observer. This is based on the theory that approaching matter appears brighter because of relativistic beaming. Previous observations of the black hole's jet showed that the black hole's spin axis is inclined at an angle of 17° relative to the observer's line of sight.[1] From these two observations, EHT concluded the black hole spins clockwise, as seen from Earth.[1][17]

Images were created independently by four teams to assess the reliability of the results.[18] These methods included both an established algorithm in radio astronomy known as CLEAN as well as more advanced data processing methods. Doctoral dissertation work by Katie Bouman, an American computer scientist, was instrumental in the development of this strategy.[18]

Contributing institutions

A schematic diagram of the VLBI mechanism of EHT. Each antenna, spread out over vast distances, has an extremely precise atomic clock. Analogue signals collected by the antenna are converted to digital signals and stored on hard drives together with the time signals provided by the atomic clock. The hard drives are then shipped to a central location to be synchronized. An astronomical observation image is obtained by processing the data gathered from multiple locations.

Some contributing institutions are:[19][20]

References

  1. ^ a b c d e The Event Horizon Telescope Collaboration (April 10, 2019). "First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole". The Astrophysical Journal Letters. 87 (1): L1. doi:10.3847/2041-8213/ab0ec7.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  2. ^
  3. ^
  4. ^ Chan, Tracy (April 10, 2019). "Hawaii Telescopes Helped Capture the First Image of a Black Hole – and It Has a Hawaiian Name". Hawaii Magazine. Retrieved April 11, 2019.
  5. ^ a b O'Neill, Ian (July 2, 2015). "Event Horizon Telescope Will Probe Spacetime's Mysteries". Discovery News. Retrieved August 21, 2015.
  6. ^ "MIT Haystack Observatory: Astronomy Wideband VLBI Millimeter Wavelength". www.haystack.mit.edu.
  7. ^ Webb, Jonathan (January 8, 2016). "Event horizon snapshot due in 2017". BBC News. Retrieved March 24, 2016.
  8. ^ a b Davide Castelvecchi (March 23, 2017). "How to hunt for a black hole with a telescope the size of Earth". Nature. 543 (7646): 478–480. Bibcode:2017Natur.543..478C. doi:10.1038/543478a. PMID 28332538.
  9. ^ "EHT Status Update, December 15 2017". eventhorizontelescope.org. Retrieved February 9, 2018.
  10. ^ Mearian, Lucas (August 18, 2015). "Massive telescope array aims for black hole, gets gusher of data". Computerworld. Retrieved August 21, 2015.
  11. ^ Overbye, Dennis (April 10, 2019). "Black Hole Picture Revealed for the First Time – Astronomers at last have captured an image of the darkest entities in the cosmos". The New York Times. Retrieved April 10, 2019.
  12. ^ Landau, Elizabeth (April 10, 2019). "Black Hole Image Makes History". NASA. Retrieved April 10, 2019.
  13. ^ "Media Advisory: First Results from the Event Horizon Telescope to be Presented on April 10th". Event Horizon Telescope. April 1, 2019. Retrieved April 10, 2019.
  14. ^ a b c "Astronomers Capture First Image of a Black Hole". European Southern Observatory. April 10, 2019. Retrieved April 10, 2019.
  15. ^ a b Lisa Grossman, Emily Conover (April 10, 2019). "The first picture of a black hole opens a new era of astrophysics". Science News. Retrieved April 10, 2019.
  16. ^ Jake Parks (April 10, 2019). "The nature of M87: EHT's look at a supermassive black hole". Astronomy. Retrieved April 10, 2019.
  17. ^ Susanna Kohler (April 10, 2019). "First Images of a Black Hole from the Event Horizon Telescope". AAS Nova. Retrieved April 10, 2019.
  18. ^ a b The Event Horizon Telescope Collaboration (2019). "First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole". ApJL. 87 (1): L4. doi:10.3847/2041-8213/ab0e85.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  19. ^ "Affiliated Institutes". eventhorizontelescope.org. Retrieved April 10, 2019.
  20. ^ Funding Support

Further reading

External links

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