The radio emission in Sagittarius A* is generated by high-energy electrons zipping around magnetic field lines. The large polarization measurements provide that proof. Without these magnetic fields, the models predict, accretion would halt and jets would falter.Īlthough this was described in the models, what was needed was observational evidence. This tugging and pulling generates the viscosity that is needed to mediate the flow of angular momentum and permit black holes to grow. The dancing magnetic fields can loop and twist and pull the material that is falling in, and couple it with material that is flowing away from the black hole. So for a black hole to grow, some physical process must remove angular momentum from the gas that is falling in, presumably transferring it outward to material that ultimately escapes gravity’s tug. The Earth doesn’t fall into the sun, thanks to the conservation of angular momentum. To explain how a black hole grows, the theoretical models had to deal with angular momentum. But now, with the data from the EHT, scientists can begin to see how these processes work in practice. It will also shed light on the reverse process, whereby some black holes are capable of launching outflows of energy and material at nearly the speed of light, extending the black hole’s impact to intergalactic scales.ĭecades of theoretical work, including enormous computer simulations, painted a picture of how strong magnetic fields near the black hole horizon contribute to the processes that enable a black hole to grow. But the data from the Event Horizon Telescope opens a window on the inner workings of how material spirals towards black holes, finally disappearing across their event horizons, and growing into what Broderick calls “monsters lurking in the night.” They can even outshine their host galaxies in some instances.Ĭompared to some black holes, Sagittarius A* is much more anemic and fails to outshine a single bright star despite its comparatively enormous mass. But as black holes feast on the surrounding gas and stars, their accretion disks can shine and produce extraordinary energy. Broderick’s work involves analyzing and interpreting the data that come from the array.īlack holes are regions of spacetime where gravity is so strong that “what goes into them does not come out,” Broderick says.Īs the name implies, black holes are intrinsically dark, with no light or matter able to escape once they have passed the threshold of no return, known as the event horizon. When trained on the black hole at the centre of our galaxy, Sagittarius A*, it can see the structural details in the accretion flow that surrounds the black hole horizon. The discovery was made using the Event Horizon Telescope, a linked array of millimetre-wavelength telescopes that spans the globe and is set to take the highest-resolution images in the history of astronomy. The discovery, published in 2015 in the journal Science, moves the understanding of how black holes grow from the realm of theoretical speculation to the territory of empirical fact, Broderick says.īroderick was part of a collaboration that discovered high levels of polarization in the radio emission from Sagittarius A*, the bright radio source believed to be the astronomical manifestation of the 4.5-million-solar-mass black hole at the centre of the Milky Way. Were these magnetic fields not there, “a lot of theoretical astrophysics would have to go back to the drawing board,” says Avery Broderick, an Associate Faculty member at Perimeter Institute jointly appointed at the University of Waterloo. Originally Published: Augon InsideThePerimeter.ca.įinally, the stories we tell about black holes are being validated.Īstronomers have detected evidence of black-hole-scale magnetic fields near the black hole at the centre of the Milky Way galaxy.
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