The gas swirling around Sagittarius A*, the supermassive black hole at the center of the Milky Way, is richer in heavy elements than the Sun, according to a new study using the James Webb Space Telescope, Phys.org reported.
The research, led by McGill University PhD student Nicole Ford at the university's Trottier Space Institute and published in The Astronomical Journal, used Webb's MIRI MRS instrument to map the central 0.1 parsec around the black hole — a region that includes the Galactic Center Minispiral, a structure of warm ionized gas and dust. The team found the gas carries roughly 1.8 times the Sun's abundance of heavy elements, or "metals," a term astronomers use for any element heavier than hydrogen and helium.
The detected metals include neon, argon, sulfur, nickel, and iron, and the most likely source is generations of stars that lived and exploded near the galaxy's center, the Cosmic Herald reported. The gas also resembles the composition of many stars orbiting the black hole, suggesting the gas and the stars may have formed together.
The finding bears on a long-standing puzzle: why the Milky Way's central black hole feeds so slowly. "We know there's a black hole at the center of our galaxy pulling material into itself, but we see that it's eating a lot less material than other supermassive black holes, and more slowly," Ford said, according to Sky Nightly. Because metals cool gas faster than hydrogen and helium, the metal content affects how readily gas can be drawn into a black hole — making this measurement one input into any explanation of how Sagittarius A* gathers material.
The work, announced by McGill University on October 19, complements another recent study that found the gas emission around the black hole is shaped mostly by local conditions rather than past outbursts, according to Phys.org. Ford said understanding the black hole's feeding behavior will require comparing these observations with simulations of how gas evolves over longer timescales — a job Webb's unprecedented infrared resolution is only beginning.