Black hole, finally see you

At 21 o’clock on April 10, 2019, Beijing time, Belgium, Brussels, Chile, Shanghai, China, Shanghai, Taipei, Japan, Tokyo, the United States, Washington and other countries held a global press conference and released the first “Event Vision Telescope”. A major achievement, a real shot of the first black hole in human history.

We know that any equipment that is photographed needs light or electromagnetic waves to illuminate the object and then reflect back to the device for imaging. Black holes absorb light and electromagnetic waves, and no light or electromagnetic waves are reflected back. It is very difficult for humans to find black holes, let alone filming. So how do scientists do it?

The key to finding black holes is to find their “peripheries” – “accumulation discs” and “sprays.” The strong gravity of the black hole will pull the nearby matter to your side. These substances will rotate around the black hole and eventually fall into it. This process is called “accumulation”, and the disc-like structure formed when the material is bypassed is called It is an “accumulation plate”. When the accretion gas is excessive, a part of the gas is ejected in the direction of rotation under the action of the magnetic field before falling into the black hole interface to form a jet. The “accumulation disc” and “spray” phenomena are heated to high temperatures of billions of degrees Celsius due to high-speed motion, and emit intense radiation, which is easily detected by scientists on Earth through telescopes, so black holes are also There are traces to follow.

So how do you take pictures of black holes? The “Event Vision Telescope” is such an experimental plan designed to capture black hole images. The project’s main observation targets are two: one is the massive mass black hole Sagittarius A in the center of the Milky Way, and the other is the black hole in the center of the Virgo A galaxy. The two black holes were chosen as the target of observation because their visual interfaces appear to be the largest on the earth. Other black holes are more difficult to observe because they are farther away from the earth or have limited mass.

To image a black hole, you need a telescope that is as large as the Earth, which is not possible with any single telescope on Earth. For more than a decade, scientists at the Event Vision Telescope have used eight radio telescopes around the world to form a network that uses interferometry to simultaneously observe black holes. Each radio telescope collects and records electromagnetic wave signals from nearby black holes, then integrates the data and calculates an “image of the event horizon.” In order to increase the spatial resolution and see smaller areas, these radio telescope arrays also include radio telescopes in Chile and the South Pole.

The “weapons” for shooting black holes are there, and the next step is to wait for the capture. To ensure that the eight radio telescopes see the two black holes at the same time, the observation window left to the scientists is very short, only about 10 days per year. Among them, Chile’s ALMA telescope has a series of observation plans because of its highest sensitivity, and the schedule is very full. This time, the observation of the black hole interface, the ALMA telescope can only be free for four days, including two nights to observe the massive black hole Sagittarius A in the center of the Milky Way, and the rest of the time is left to the black hole in the center of the Virgo A galaxy.

Taking a photo of a black hole is not easy, and “washing photos” is a long time. The site area involved in the “Event Vision Telescope” observation spans the northern and southern hemispheres, and the amount of data generated is also very large. In the five days of observation in 2017, each radio telescope will collect more than 500 TB of data, and the entire array will generate about 7,000 terabytes of data. This huge amount of information cannot be transmitted by the network, and only the hard disk can be used to record data. At the end of the observations, each site will centrally ship these data hard drives to two data centers by mailing – the Haystack Observatory in Massachusetts and the Max Planck Institute for Astronomy in Bonn, Germany. There, the mainframe cluster will combine and analyze all of the data, and the calibrated data will be integrated to produce images with excellent resolution.

You may remember that one of the radio telescopes is located in the South Pole. The extreme climate there caused no flights to flights from February to October each year, so the hard drive was not shipped until October 2017, and it took a month to get to the destination. Since then, scientists have spent another year waiting for the supercomputer to merge and analyze the data.

Finally, we waited until the first photo of the black hole, how lucky.