Event Horizon Telescope Array

2 Years of the First Black Hole Image: Meet the Array of 8 Telescopes That Made it Possible.

Two years ago, on this day, research in astrophysics reached a major milestone when scientists released the first black hole image taken by the Event Horizon Telescope. The concept of black holes dates back to 1784. It took us more than two centuries to peer at one of the most exotic objects in the universe. To accomplish the task, scientists chose the supermassive black hole at the center of the elliptical galaxy M87, lying at a distance of 55 million light years. For your reference, a light year is roughly equal to 6 trillion miles.

1st black holes image
The first black hole image released in 2019 (Credits: Event Horizon Telescope)

Although the supermassive black hole is mammoth in itself, it subtends a minimal angle in the sky because of its large distance from the Earth. Because of the limitations imposed by optics’ laws, we needed a telescope as big as the Earth to capture the black hole. So, scientists built one! Well, not literally. The Event Horizon Telescope is a combination of eight radio telescopes located around the globe. Each of these telescopes had a unique role to play.

Sub-Millimeter Array (SMA, Hawaii)

Event Horizon Telescope array
Sub-Millimeter Array, Hawaii (Image: Afshin Darian, CC BY 2.0)

Located near the summit of Maunakea in Hawaii, the Sub-Millimeter Array is known as a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics. The array consists of eight 6-meter radio telescopes, which operate at frequencies ranging from 180 GHz to 420 GHz. Due to atmospheric instability during the day, it’s most observations take place during the nighttime.

Sub-Millimeter Telescope (SMT), Eastern Arizona

Event Horizon Telescope array
Photo of 12 meter radio telescope on Kitt Peak, Arizona, USA. (Photo taken by Jeff Mangum of the NRAO)

Formerly known as Heinrich Hertz Submillimeter Telescope, the telescope is located at the height of 3200 m on Mount Graham in eastern Arizona. Although the telescope has been operating for over 25 years, it has continued to get better. Currently, it boasts of a 10 m primary parabolic mirror and operates at frequencies of 200 GHz to 2 THz, having a precision of 1’’ (1 arc-second).

Large Millimeter Telescope (LMT), Mexico

Event Horizon Telescope array
Image: Sciencemag.org, DARIO LOPEZ-MILLS

As the name suggests, this telescope is the biggest millimeter-Telescope ever built, spanning a diameter of over 50 meters. Located on the fifth highest peak in Mexico, it played a crucial role in developing the first picture of the black hole. The telescope has been operating since the mid of 2011 and has managed to pierce 13 billion years into the history of the universe’s existence.

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IRAM 30m Telescope (IRAM), Spain

Event Horizon Telescope array

The IRAM 30 m millimeter radio telescope is operated by Institute for Radio Astronomy in the Millimeter Range (IRAM). It is located in the Sierra Nevada in Spain at an altitude of 9350 ft (2850 m). This Bad Boy is the second-largest radio telescope in the world after the LMT (Large Millimeter Telescope) but has been much more accurate than its older competitor. The Telescope sits upon its humongous Altazimuth mount, which helps it achieve a precision of over 10 arc seconds!

James Clerk Maxwell Telescope (JCMT), (Hawaii)

Event Horizon Telescope array
The JCMT (Image: William Montgomerie)

Named after the Scottish physicist James Clerk Maxwell, the telescope is located near the summit of MaunaKea in Hawaii. Its primary mirror spans a little over 15 meters and is the largest single-dish telescope operating at the sub-millimeter range. Later, it was combined with the Caltech Sub-millimeter Observatory, forming the first sub-millimeter interferometer, which eventually resulted in the construction of the Sub-millimeter array (SMA) and The Atacama Large Millimeter Array (ALMA). 

Atacama Large Millimeter Array (ALMA), Chile

Event Horizon Telescope array
Credit: ESO/C. Malin

The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer consisting of 66 radio telescopes. Located in the Atacama desert of Chile, it was constructed with a cost of approx. $1.4 Billion, making it the most expensive ground-based telescope to date. ALMA is an international partnership among Europe, the United States, Canada, Japan, South Korea, Taiwan, and Chile.

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Atacama Pathfinder Experiment (APEX), Chile

Event Horizon Telescope array
Image: ESO/H.H.Heyer 

The APEX Telescope is a 12-meter diameter telescope, operating at millimeter and submillimetre wavelengths, located on the ALMA observatory site. APEX is a modified ALMA prototype antenna and is a collaboration between the German Max Planck Institute for Radio Astronomy (MPIfR), the Swedish Onsala Space Observatory (OSO), and the European Organisation for Astronomical Research in the Southern Hemisphere (ESO). Its primary purpose is to find targets for much detailed study by ALMA.

South Pole Telescope (SPT), Antarctica

Event Horizon Telescope array
Image: Kavli Institute of Particle Astrophysics and Cosmology

Located in Antarctica, the South Pole Telescope is designed primarily for Cosmic Microwave Background observations (CMB). With little or no light pollution, this 10-meter telescope is one of the sharpest Event Horizon Telescopes in operation.

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