Embedded Files
The sky that Earth observes is divided into "Southern Sky" and "Northern Sky" because of the observer's location in the southern or northern hemisphere, respectively. Each corresponds to some celestial bodies suitable for observation. Currently, for the Southern Sky the submillimeter very long baseline array has formed a triangle with three points: "South Pole Telescope" (located in Antarctica, abbreviated as "SPT"), "Sub-Millimeter Array" (located in Hawaiʻi, abbreviated as "SMA"), and "Atacama Large Millimeter Array" (located in Chile, South America, abbreviated as "ALMA").
What about the Northern Sky?
A few years ago, astronomers from ASIAA proposed that they could help the SMA and ALMA find a third point to form another triangle. The third telescope should be best located on the Greenland Island within the Arctic Circle for maximum triangle area. Why are SMA and ALMA the two points that are given priority when considering the optimal placement of a third point? It turns out that these two telescope projects have been planned for a long time by Taiwan's astronomical community. Taiwan has been involved since their construction and has continued to contribute. Not only having rich experience but also usage rights, this has formed unique advantages of Taiwan as an existing asset invested in astronomical research.
The badge designed for the Greenland Telescope project, demonstrates the project goal: building a gigantic telescope with an aperture equivalent to the diameter of Earth, for imagining the black holes and exploring the unknown beyond.
The upper right red vertex of the triangle is at Greenland, left vertex at Hawaiʻi, and the bottom one is the ALMA in Chile.
(Credit: NCSIST, Bill Liu)
Do the math, there are dozens of triangles on this map! While there are many options for how to connect the triangle, selecting Greenland as the third point besides SMA and ALMA may be the one most conducive to Taiwan's contribution to the development of global astronomy.
There are several submillimeter wavelength telescopes (observatories) shown on this map, which respectively are the SMA and the EAO in Hawaiʻi, and the ALMA in Chile, all being members of the global very long baseline interferometer array.
Viewed on Google Earth, the triangle drawn by the three points forms 9,000-kilometers-long baselines. In the interferometry of radio telescopes, the baseline length implies the aperture size of the (virtual) telescope. Therefore this virtual telescope created by interferometry can be said to be "almost as big as the Earth".
Image source: https://www.cfa.harvard.edu/greenland12m/science/
Choosing Greenland within the Arctic Circle as the location for the third telescope is another equally important consideration in addition to the aforementioned reasons. “Atmospheric transparency” refers to the degree of absorption of radio signals by the atmosphere. The more absorption there is, the more shielding there is, and the lower the transparency. This is because the Earth’s atmosphere contains water vapor, which blocks radio signals at specific wavelengths. The shorter the wavelength of the radio wave, the easier it is to be blocked. In order to minimize this effect of atmospheric shielding on radio signals, radio telescopes are mostly built in high-altitude and dry areas where water has frozen into ice and there is naturally less water vapor in the atmosphere.
The Summit Station at Greenland has an altitude of 3,200 meters and hence high atmospheric transparency. It has been proven by actual measurements that it is extremely suitable for submillimeter wavelength observations and has become the third point of the Golden Triangle composed of “Greenland-SMA-ALMA”, taking into account all of these factors.
After this Golden Triangle is established, it is expected that the angular resolution will be several tens of microarcseconds. This extremely fine angular resolution gives us a chance to resolve the “event horizon” of supermassive black holes at the centers of galaxies.
The climate conditions in the Arctic Circle are extremely harsh. In order to enable telescopes to operate in polar environments, the engineering teams of our institute and NCSIST have cooperated to upgrade telescope performance as shown in the figure below.
The cables in the small circles in the left picture are the "de-ice system" that the engineering team has installed on the entire antenna dish surface, ready to allow the telescope to be heated. The picture on the right shows that after the de-icing system is laid out, the engineering team begins to assemble the mirrors on the antenna dish. The antenna has a diameter of 12 meters, equivalent to an area about half of a basketball court.
(image credit: ASIAA)
Report abuse