For the first time in history, astronomers have been able to observe in the same image the shadow of the black hole at the center of the galaxy Messier 87 (M87) and a powerful jet of material, also called a jet. The discovery was announced by the European Southern Observatory (ESO). According to scientists, this will help to better understand how black holes work.
A big part galaxies has supermassive black holes at its centers. These objects are known to absorb matter from their immediate surroundings, but they can also shoot powerful jets of matter (jet streams) that extend even beyond the galaxies in which they reside. Understanding how black holes create these types of giant jets has puzzled astronomers for years.
“We know that jets are ejected from the region surrounding black holes,” said Ru-Sen Lu of the Shanghai Astronomical Observatory in China. But we still don’t fully understand how it actually happens. To study this directly, we need to observe the source of the jet as close to the black hole as possible, he added.
The image released on Wednesday for the first time clearly shows the issue: how the base of the jet merges with the material swirling around the supermassive black hole. The target is the galaxy Messier 87 (M87), located 55 million light years away in our cosmic neighborhood, which is home to a black hole 6.5 billion times more massive than the Sun.
The black hole shoots out a powerful jet
Thanks to previous observations, it was possible to image the area close to the black hole and the jet separately. This time, for the first time, the two structures have been captured together. ‘The new image completes the picture by showing the region around the black hole and the jet at the same time,’ commented Jae-Young Kim from Kyungpook National University in South Korea and the Max Planck Institute for Radio Astronomy in Germany.
The image was obtained with the Global Millimeter VLBI Array (GMVA), the Atacama Large Millimeter/submillimeter Array (ALMA), of which the European Southern Observatory (ESO) is a partner, and the Greenland Telescope (GLT). They all form a network of radio telescopes around the globe, working together as a virtual Earth-sized telescope. Such a large network can distinguish fine details in the region around M87’s black hole.
The new image shows a jet starting close to the black hole, as well as what scientists call a black hole shadow. As matter orbits a black hole, it heats up and emits light. A black hole bends and captures some of this light, forming a ring-like structure around itself when viewed from Earth. The darkness at the center of the ring is the shadow of a black hole that was first imaged by the Event Horizon Telescope (EHT) in 2017. Both images, the most recent and the one from the EHT, combine data from many radio telescopes around the world, but the image presented today shows radio waves emitted at longer wavelengths than EHT (3.5 millimeters instead of 1.3 mm).
– At this wavelength, we can see a jet being born from the ring of emission around the central supermassive black hole – commented Thomas Krichbaum of the Max Planck Institute for Radio Astronomy.
Observations of the black hole in M87
The size of the ring observed by the GMVA network is almost 50 percent larger compared to the image from the Event Horizon Telescope. “To understand the physical source of the larger and thicker ring, we need to use computer simulations to test different scenarios – translated Keiichi Asada from Academia Sinica in Taiwan. The results suggest that the new image reveals more material falling towards the black hole than could be observed by the EHT.
New observations of the black hole in M87 were made in 2018 with the help of the GMVA network, which includes 14 radio telescopes in Europe and North America. In addition, two other observatories were connected to GMVA at that time: the Greenland Telescope and ALMA, in which ESO is a partner.
The ALMA network contains 66 antennas in the Chilean Atacama Desert and played a key role in these observations. The data collected by all the telescopes around the world are combined using a technique called interferometry, which synchronizes the signals received by the various devices. But in order to get the true shape of an astronomical object correctly, it is important that telescopes are spread all over the Earth. GMVA’s telescopes are mostly east-west, so the addition of ALMA from the southern hemisphere was crucial in capturing the image of the jet and shadow of M87’s black hole. “Thanks to ALMA’s positioning and sensitivity, we can reveal the shadow of the black hole and see the emission from the jet deeper, both at the same time,” Lu noted.
Future observations with this network of telescopes will continue to reveal more about how the supermassive black hole fires powerful jets. – We plan to observe the region around the black hole at the center of M87 at different radio wavelengths to further study the emission from the jet – said Eduardo Ros from the Max Planck Institute for Radio Astronomy. Such simultaneous observations will allow the team to unravel the complex processes that occur in the vicinity of a supermassive black hole. “The coming years will be interesting as we’ll be able to learn more about what’s going on close to one of the most puzzling regions in the universe,” Ros concluded.
Main photo source: R.-S. Lu (SHAO), E. Ros (MPIfR), S. Dagnello (NRAO/AUI/NSF), European Southern Observatory