What is the goal of this project?

Joining the submillimeter very long baseline interferometer array is of great help to our institute’s research in supermassive black holes because submillimeter waves have about 10 times finer angular resolution than millimeter arrays. This is just enough for us to see larger black holes that are closer.

Very Long Baseline Interferometry (abbreviated as “VLBI”) is a technique that combines the resolution and data of telescopes around the world to create a virtual and huge radio telescope. If anyone wants to know what its resolution is for a radio telescope, it can be simply derived by a formula with the “radio wavelength” and “telescope aperture size”. The calculation is radio wavelength divided by antenna diameter. The smaller this ratio is, the better the angular resolution will be. In the terms of VLBI, “aperture size” comes from the distance between individual antennas. The submillimeter wavelength is shorter by one order of magnitude, and hence provides higher angular resolution.

You may know that there are not many supermassive black holes close to us. The two most famous ones are Sagittarius A* in the center of our Milky Way galaxy, and another one M87* located in the core of M87 galaxy (both are tens of millions of light-years away from the Earth). But what you may not know is that although supermassive black holes have a large mass, their volume may be small. For example, M87* its volume is only about as large as Neptune’s orbit around the Sun. If Taiwan is used as an analogy for the entire M87 galaxy’s volume, then M87* at its center would be as small as a grain of rice. However, its weight accounts for a ratio like Taipei City to Taiwan. In summary, if we want to observe black hole shadows, our telescope’s angular resolution must be very good - even if we only want to observe supermassive black holes closest to us, our resolution must reach down to several tens of microarcseconds.

The team of ASIAA estimated that the angular resolution can achieve several tens of microarcseconds when the golden triangle "Greenland-SMA-ALMA" is formed, enough to resolve the supermassive black hole at the core of M87 galaxy. If turning this kind of resolving power into visual comparison, this is like being able to see a coin on the Moon from the Earth.

To be more specific, "imaging the shadow of a black hole" means seeing the event horizon which is the boundary that defines the region influence by the black hole. Read this article "Event horizon, why is it so interested? MISSING LINK" for further details.

>> MAYBE NEED TO REPLACE WITH A MORE APPROPRIATE FIGURE. <<

這是次毫米波特長基線干涉儀在格陵蘭望遠鏡加入後可望取得的M87黑洞陰影之電腦模擬。

角解析力為40微角秒。

電腦模擬圖像取得方法是「光束追蹤法」。

電腦模擬運算條件為：一個質量為太陽60億倍的超大質量黑洞，處於無自旋狀態、黑洞周圍透光度高（有陰影）、且物質呈自由掉落狀態（角動量未計算）。

(Credit: ASIAA, VLBI/GLT Team)