The Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) has discovered a cloud of cosmic dust at the center of the galaxy Messier 77 that conceals a supermassive black hole. The discoveries back up predictions made more than 30 years ago, and they provide scientists with fresh information on “active galactic nuclei,” some of the brightest and most intriguing objects in the cosmos.
AGNs are very intense sources driven by supermassive black holes that may be located at the center of certain galaxies. Large amounts of cosmic dust and gas are consumed by these black holes. This material spirals towards the black hole before being swallowed up, releasing massive quantities of energy and often outshining all of the galaxy’s stars in the process.
AGNs have piqued the interest of astronomers since they were first discovered in the 1950s. Now, due to ESO’s VLTI, a team of researchers headed by Violeta Gámez Rosas of Leiden University in the Netherlands has made a significant step toward understanding how they operate and how they seem up close. The findings were published in Nature today.
Gámez Rosas and her colleagues discovered a thick ring of cosmic dust and gas covering a supermassive black hole by performing very precise measurements of the center of the galaxy Messier 77, also known as NGC 1068. This revelation adds to the support for the Unified Model of AGNs, which has been around for 30 years.
Different kinds of AGN are known to astronomers. Certain AGNs, for example, emit bursts of radio waves while others do not; some AGNs flash brilliantly in visible light while others, such as Messier 77, are less so. Despite their peculiarities, all AGNs, according to the Unified Model, have the same fundamental structure: a supermassive black hole surrounded by a thick ring of dust.
Any differences in appearance between AGNs, according to this hypothesis, are due to the angle at which we see the black hole and its thick ring from Earth. The sort of AGN we see is determined by how much the ring obscures the black hole from our perspective, sometimes entirely obscuring it.
Astronomers have already discovered evidence to support the Unified Model, such as heated material near the center of Messier 77. However, questions persisted regarding whether this dust could totally conceal a black hole and hence explain why this AGN flashes in visible light less brilliantly than others.
“Over the past three decades, major concerns in AGN research have been the true nature of the dust clouds and their involvement in both feeding the black hole and dictating how it appears when observed from Earth,” Gámez Rosas notes. “While no one discovery will answer all of our issues, we have made significant progress in our knowledge of how AGNs operate.”
The observations were made possible by the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE), which is placed on ESO’s VLTI in the Atacama Desert of Chile. MATISSE used interferometry to integrate infrared light gathered by all four 8.2-meter telescopes of ESO’s Very Large Telescope (VLT). The scientists utilized MATISSE to scan the center of Messier 77 in the constellation Cetus, which is 47 million light-years distant.
“MATISSE can observe a wide spectrum of infrared wavelengths, allowing us to see through dust and monitor temperatures precisely. We have the resolution to observe what’s going on even in galaxies as far away as Messier 77 because the VLTI is a very massive interferometer. The photos we collected show the temperature and absorption fluctuations in the dust clouds around the black hole “Walter Jaffe, a professor at Leiden University, is one of the co-authors.
The scientists created a precise image of the dust by combining the fluctuations in dust temperature (from roughly room temperature to around 1200 °C) generated by the strong radiation from the black hole with the absorption maps, and determined where the black hole must reside. The Unified Model is supported by dust, which is arranged in a thick inner ring and a wider disc, with a black hole at its center. The scientists also constructed their image using data from the Atacama Large Millimeter/submillimeter Array, which is co-owned by ESO, and the National Radio Astronomy Observatory’s Very Long Baseline Array.
“Our findings should lead to a greater understanding of how AGNs operate,” Gámez Rosas says. “They may also aid our understanding of the Milky Way’s history, since it contains a supermassive black hole at its center that may have been active in the past.”
By looking at a broader sample of galaxies, the researchers hope to uncover further evidence for the Unified Model of AGNs using ESO’s VLTI.
“Messier 77 is an important prototype AGN and a tremendous motivator to extend our observation programme and to optimize MATISSE to handle a bigger sample of AGNs,” said team member Bruno Lopez, the MATISSE Principal Investigator at the Observatoire de la Côte d’Azur in Nice, France.