Most galaxies harbor a supermassive black hole at their center. While black holes are known to gobble up matter in their immediate vicinity, they can also launch powerful jets of matter from their immediate vicinity that extend beyond the galaxies in which they reside. How black holes create such huge jets has long been a mystery.
Jets are known to be ejected from the region surrounding black holes, but how this happens has not been clear. To study it directly, it is required to observe the origin of the jet as close as possible to the black hole.
Ru-Sen Lu’s team, from the Shanghai Astronomical Observatory in China, has managed to obtain an image that shows for the first time how the base of a jet connects with matter revolving around a supermassive black hole. The phenomenon has been seen at the center of the galaxy M87, located 55 million light-years away from Earth, and home to a black hole 6.5 billion times more massive than the Sun. Previous observations had been successful in obtaining images separated from the region near the black hole and the jet, but this is the first time the two have been observed together. “Now, by showing the region around the black hole and the jet at the same time, we already have the full picture,” adds Jae-Young Kim, of Kyungpook National University in South Korea and the Max Planck Institute for Radio astronomy, in Germany.
The image was obtained with the GMVA, ALMA and GLT observatories, forming a global network of radio telescopes that have worked together as a virtual Earth-sized radio telescope. Such a large grating can discern very small details in the region around M87’s black hole.
The new image shows the jet emerging near the black hole, as well as what scientists call the black hole’s shadow. As matter orbits the black hole, it heats up and emits light. The black hole bends and captures some of this light, creating a structure around the black hole that, when viewed from Earth, looks like a ring. The darkness at the center of the ring is the shadow of the black hole, which was first imaged by the EHT (Event Horizon Telescope) in 2017. Both this new image and the EHT image combine data taken with several radio telescopes spread around the world. , but the new image shows the radio wave emissions emitted at a longer wavelength than that observed by the EHT: 3.5 millimeters instead of 1.3. “At this wavelength, we can see the jet emerging from the emission ring around the central supermassive black hole,” says Thomas Krichbaum of the Max Planck Institute for Radio Astronomy.
The size of the ring observed by the GMVA network is approximately 50% larger compared to the EHT image. “To understand the physical origin of the largest and thickest ring, we had to use computer simulations to test different scenarios,” explains Keiichi Asada of Academia Sinica in Taiwan. The results suggest that the new image reveals that there is more material falling towards the black hole than could be observed with the EHT.
This image shows the jet and the shadow of the black hole at the center of the galaxy M87 together for the first time. The observations were obtained with radio telescopes from the Global Millimeter VLBI Array (GMVA), the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, and the Greenland Radio Telescope. This image gives scientists the context they need to understand how the powerful jet forms. The new observations also revealed that the black hole’s ring, highlighted in the inset, is 50% larger than the ring observed at shorter radio wavelengths by the Event Horizon Telescope (EHT). This suggests that we see more of the material falling towards the black hole in the new image than we could with the EHT. (Image: R.-S. Lu (SHAO), E. Ros (MPIfR), S. Dagnello (NRAO/AUI/NSF). CC BY 4.0)
These new observations of M87’s black hole were made with GMVA, which consists of 14 radio telescopes in Europe and North America. In addition, two other facilities were linked to GMVA: the Greenland Radio Telescope and ALMA, of which the European Southern Observatory (ESO) is a partner. ALMA consists of 66 antennas in the Chilean Atacama Desert, and played a key role in these observations. The data collected by all these radio telescopes around the world is combined using a technique called interferometry, which synchronizes the signals taken by each individual facility. But to adequately capture the real shape of an astronomical object it is important that radio telescopes are spread all over the Earth. The radio telescopes in the GMVA network are mostly aligned from east to west, so the addition of ALMA in the southern hemisphere was essential to capture this image of M87’s black hole jet and shadow. “Thanks to ALMA’s location and sensitivity, we were able to reveal the shadow of the black hole and, at the same time, see more deeply into the emission from the jet,” explains Lu.
In the future, observations with this network of radio telescopes will continue to unravel how supermassive black holes can launch 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,” confirms Eduardo Ros from the Max Planck Institute for Radio Astronomy. These simultaneous observations would allow the team to unravel the complicated processes taking place near the supermassive black hole. “The next few years will be exciting, as we will be able to learn more about what is happening near one of the most mysterious regions of the universe,” concludes Ros.
The study is titled “A ring-like accretion structure in M87 connecting its black hole and jet”. And it has been published in the academic journal Nature. (Source: IT)