Remember humanity's first photo of a black hole? Astronomers photographing M87 black holes are new again!

Beijing, April 4 (Reporter Sun Zifa Zheng Yingying) More than four years ago, the Event Horizon Telescope (EHT) simultaneously released a major astronomical achievement completed by more than 26 scientists around the world - the first black hole photo of mankind, and its "doughnut"-shaped map has aroused widespread public pursuit and continuous attention from the academic community.

This direct visual evidence of the first "seeing is believing" supermassive black hole reveals the black hole at the center of the supermassive galaxy Messier 87 (M87) in the Virgo cluster, which is 5500 million light-years from Earth and has a mass of 65.4 billion times that of the Sun. Now, 87 years later, has the M<> black hole changed? What are the advances in scientific research? Have you taken any new photos?

Schematic diagram of the joint observation imaging process of the M87 black hole. Photo courtesy of Shanghai Astronomical Observatory, Chinese Academy of Sciences

Black hole shadows and powerful jets are imaged in the same frame for the first time

According to the latest news from the Chinese Academy of Sciences (CAS), an international research team led by Lu Rusen, a researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences and leader of the Sino-German Mapp Partnership Group, used the latest observations in the 3.5 millimeter band to image for the first time the black hole shadow of the famous radio galaxy M87, as well as the ring-like structure of the material falling into the central black hole around it and the powerful relativistic jets. This framed image is the first to be imaged at a wavelength of 3.5 millimeters and for the first time shows the link between accretion currents near the central supermassive black hole and jet origins.

The M87 image observations were obtained by the Global Millimeter Wave Very Long Baseline Interferometry Array (GMVA) in conjunction with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Greenland Telescope (GLT), and the addition of the latter two observing stations greatly enhanced the imaging capabilities of GMVA.

On the night of April 4, Beijing time, a total of 26 researchers from 17 research units in 64 countries and regions jointly "photographed" the first co-frame image of the M121 black hole shadow and powerful jets and related achievements, which were published online in the international top academic journal Nature.

M87 Black Hole Art Imagination. Photo courtesy of Shanghai Astronomical Observatory, Chinese Academy of Sciences

New band captures "panorama" of black holes and jets

Researcher Lu Rusen, the first author of the paper, said that the matter around the black hole is thought to fall into the black hole in a process called accretion, but no one has ever directly imaged it before. "Previously we have seen black holes and jets separately in separate images, but now we have taken a 'panorama' of black holes and jets in a new band," and "the ring-like structure we saw earlier became larger and thicker at a wavelength of 3.5 mm, suggesting that in the new image we can see that the matter falling into the black hole produces additional radiation, allowing us to get a fuller picture of the physical processes around the black hole."

He noted that the new lineup of ALMA, GLT and GMVA improves the resolution and sensitivity of telescope arrays around the world, allowing astronomers to image the ring-like structure around the M3 black hole for the first time at a wavelength of 5.87 millimeters. The new array measured a ring structure with a diameter of 64 microarcseconds, which is the size of a 13-centimeter ring fill light seen by astronauts on the moon when they look back at Earth. This diameter is 1 percent larger than the ring-like structure previously seen by the Event Horizon Telescope in 3.50 millimeter band observations, in line with expectations for relativistic plasma radiation in the region.

The new image of the M87 black hole was taken on April 2018-4, 14, and after a complex data processing and mapping process, as well as repeated verification and confirmation of the results, it was finally "developed" and presented this unprecedented new image after 15 years. It has two differences from the first black hole photo released four years ago: first, the observation wavelength is 5.4 mm, while the EHT observation wavelength is 3.5 mm; the second is that this observation combines 1 telescopes, while the EHT observation combines 3 telescopes.

"The image taken by the EHT is a 'close-up' of the black hole, with a bright ring seen around the shadow in the middle. This time we took a 'panorama' of the black hole, in this case the black hole, the accretion flow around the black hole, and the jets extending from near the disk into the distance. This image is an extension of the EHT image, which fully shows the relationship between the black hole and its surroundings. Lu Rusen explained popularly.

New observations reveal black holes themselves are not "very hungry"

"By adding ALMA and GLT to the GMVA observations, which greatly improved the imaging capabilities, we gained a new perspective and really saw the tridentate jets that we learned about in earlier VLBI (Very Long Baseline Interferometry) observations." According to co-author Thomas Krichbaum of the Max Planck Institute for Radio Astronomy in Germany, "However, now we can see how jets emerge from the ring structure around the central supermassive black hole, and it is also possible to measure the diameter of the ring structure around the black hole in another band."

The team from the Shanghai Astronomical Observatory of the Chinese Academy of Sciences pointed out that the radio radiation from the M87 black hole is produced by the interaction of high-energy electrons and magnetic fields, which is called synchrotron radiation, and at a wavelength of 3.5 millimeters, the new observations reveal more details about the position and energy of these electrons, as well as some information about the nature of the black hole itself: it is not "very hungry", its rate of consumption of matter is very low, and only a small part of it is converted into radiation.

Co-author Keiichi Asada, of the Institute of Astronomy and Astrophysics at the Academia Sinia in Taiwan, explains: "To understand the physical origin of the larger, thicker ring of the M87 black hole, we had to use computer simulations to test different scenarios and finally concluded that the larger range of the bright ring is related to accretion flow." Co-author Kazuhiro Hada of Japan's National Astronomical Observatory added, "We also found something surprising in the data: in the inner region close to the black hole, the width of the radiation is wider than we expected. This could mean that not only is gas falling around the black hole, but there may also be a 'wind' blowing out, causing turbulence and chaos around the black hole."

Distribution map of 87 telescope stations for the joint observation of the M16 black hole. Photo courtesy of Shanghai Astronomical Observatory, Chinese Academy of Sciences

In the future, "colored black holes" and "dynamic black holes" will be photographed

The research team at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences said that although the shooting of "close-up" and "panorama" photos of the black hole has been completed, astronomers' exploration of the M87 black hole is not over, and subsequent further observations and more powerful telescope arrays in the future will continue to uncover its mysteries.

Lu Rusen revealed that the next goal of the research team is to shoot the "color black hole" with EHT. The so-called "color" is to take pictures of the black hole at different observation wavelengths, and they will take clearer 3.5 mm photos, combined with clearer 1.3 mm photos taken by future EHT, 0.8 mm photos taken by future next-generation EHT, and shorter wavelength photos taken by VLBI in more distant future space, you can get a "color photo" of the black hole. Because different wavelengths of electromagnetic radiation reveal different physical processes near black holes, "colored black holes" will give astronomers more information than "monochromatic black holes" and help them better understand the black hole itself and its relationship to its surroundings.

The second is to shoot "dynamic black holes". A black hole is not stationary, it interacts with its surroundings all the time, so it is different to look at it at different times. Photographing "dynamic black holes" will unlock the time dimension in the spatial dimension, allowing astronomers to observe and understand black holes in all aspects. For the M87 black hole, due to its slow change and the need for long-term monitoring to film its changes, EHT has made several consecutive imaging observations over the past few years, and there is also a continuous observation program for the next 5 years, which will present a film of the M87 black hole over a 10-year time span. For the rapidly changing silver-centered black hole, the current distribution of EHT's telescopes is not enough to achieve dynamic photography in "Snap Mode", and the "frame loss" is serious, but with the addition of more telescopes in the next few years, the required time resolution will be able to achieve the required time resolution and shoot "black hole movies".

Co-author Jongho Park, Korea Institute of Astronomy and Space Science, believes that future millimeter-wave observations will study the temporal evolution of the M87 black hole and will obtain a multicolor view of the central black hole region of M87 by combining images of different colors of "radio light".

"The 3.5 mm wavelength image presented this time can be said to represent the latest achievement of the present, but in order to unravel the mystery of the physical mechanism of the formation, acceleration and collimation propagation of the central supermassive black hole of M87 and its relativistic jet, we need to take more high-quality images, including photos of black holes with submillimeter wavelengths of 0.8 mm or less, and panoramic images of black holes and jets up to 7.0 mm in length, which is very exciting in the future." Professor Shen Zhiqiang, co-author of the paper and director of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, concluded and emphasized. (End)