New image shows a black hole expelling a powerful jet
Astronomers have observed for the first time, in the same image, the shadow of the black hole at the centre of the galaxy Messier 87 (M87) and the powerful jet expelled from it. The observations were made in 2018 with telescopes from the Global Millimetre VLBI Array (GMVA) in Europe and North America, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Greenland Telescope (GLT).
While black holes are known for engulfing matter in their immediate vicinity, they can also launch powerful jets of matter that extend beyond the galaxies that they live in. Understanding how black holes create such enormous jets has been a longstanding problem in astronomy.
“We know that jets are ejected from the region surrounding black holes, but we still do not fully understand how this actually happens,” said Ru-Sen Lu, from the Shanghai Astronomical Observatory. “To study this directly, we need to observe the origin of the jet as close as possible to the black hole.”
The newly published image shows precisely this: how the base of a jet connects with the matter swirling around a supermassive black hole. The target is the galaxy M87, located 55 million light-years away in our cosmic neighbourhood, and home to a black hole 6.5 billion times more massive than the Sun. Previous observations had managed to separately image the region close to the black hole and the jet, but this is the first time both features have been observed together.
The image was obtained with the GMVA, ALMA and GLT forming a network of radio telescopes around the globe working together as a virtual Earth-sized telescope; such a large network can discern very small details in the region around M87’s black hole. ALMA’s position in the Southern Hemisphere proved especially useful, with Lu saying, “Thanks to ALMA’s location and sensitivity, we could reveal the black hole shadow and see deeper into the emission of the jet at the same time.”
The image shows the jet emerging near the black hole, as well as what scientists call the shadow of the black hole. As matter orbits the black hole, it heats up and emits light. The black hole bends and captures some of this light, creating a ring-like structure around the black hole as seen from Earth. The darkness at the centre of the ring is the black hole shadow, which was first imaged by the Event Horizon Telescope (EHT) in 2017. Both this new image and the EHT one combine data taken with several radio telescopes worldwide, but the new image shows radio light emitted at a longer wavelength than the EHT one: 3.5 mm instead of 1.3 mm.
“At this wavelength, we can see how the jet emerges from the ring of emission around the central supermassive black hole,” said Thomas Krichbaum, from the Max Planck Institute for Radio Astronomy. The size of the ring observed by the GMVA network is also roughly 50% larger in comparison to the EHT image; this is because the new image reveals more of the material that is falling towards the black hole than could be observed with the EHT, the researchers suggested.
“We plan to observe the region around the black hole at the centre of M87 at different radio wavelengths to further study the emission of the jet,” said Eduardo Ros from the Max Planck Institute. Such simultaneous observations would allow the team to disentangle the complicated processes that happen near the supermassive black hole.
“The coming years will be exciting, as we will be able to learn more about what happens near one of the most mysterious regions in the universe,” Ros said.
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