Dust devils swirling around black holes shed light on the cosmos By studying the clouds of matter that black holes gather, researchers hope to gain a better understanding of the universe as a whole. Space © ChiccoDodiFC, Shutterstock The universe is one vast, open space, but thanks to gravity, it is not an empty space. Scattered throughout the universe are galaxies, collections of billions of stars, gas and dust. But there’s also something lurking out there in the darkness of space – something capable of swallowing up all matter that comes its way. That something is the supermassive black hole. “While it is well known that all big galaxies have a supermassive black hole at their centre, we know very little about where and when they are born and how they grow into the spectacular masses that they are,” says astrophysicist and Marie Skłodowska-Curie fellow Daniel Asmus. With the support of the EU-funded DUSTDEVILS project, Asmus set out to shed new light on the mysteries of the galactic black hole. “By blowing material from their inner regions outward, it seems that these black holes play an important role in the evolution of galaxies,” he adds. “By better understanding black holes, we’ll also gain a better understanding of the universe as a whole.” Dust devils in space Asmus’ research focused on the growth and feedback phase of galactic black holes. During this phase, large amounts of radiation are released through the entire electromagnetic spectrum, causing a galaxy’s nucleus to shine many times brighter than the rest of the galaxy. Called active galactic nuclei (AGN), their shine is so bright that they can be seen over great cosmic distances. “During this phenomenon, a large part of the in-falling matter is lifted up from the black hole’s swirling accretion disc, somewhat like a dust devil in the desert,” explains Asmus. “These so-called dust devils have the potential to significantly advance our understanding of the AGN structure and thus were the subject of our research.” By observing a test sample of nearby galaxies, Asmus concluded that polar dust might be a ubiquitous phenomenon in AGN. “We also found tentative evidence of a physical connection between the size of the polar structure and the accretion rate of the black hole relative to its mass,” notes Asmus. “This indicates that polar dust is indeed part of a radiation-driven wind that extends from the outer, dusty accretion disc to galactic scales.” Motivated by these findings, Asmus then conducted a data-mining search for AGN in the local universe. By looking for polar dust radiating in the infrared, he was able to identify new black holes growing in highly obscured environments. According to Asmus, this work has expanded the number of known AGN by nearly 40 %. More research ahead By significantly advancing our understanding of black hole growth, the DUSTDEVILS project sets the stage for the soon-to-be launched James Webb Space Telescope. “Having established dusty polar winds as a new paradigm, the James Webb Space Telescope will be able to follow up on our work in much greater depth,” says Asmus. Asmus plans to further follow up on the obscured AGN revealed during the project. “This work has paved the way for upcoming x-ray, all-sky surveys that will complete our survey of local black hole growth,” he concludes. Keywords DUSTDEVILS, black holes, universe, space, galaxies, AGN, active galactic nuclei, polar dust
