The James Webb Space Telescope (JWST) has found that gas surrounding the Milky Way’s central supermassive black hole contains about 1.8 times the heavy elements found in the Sun. The discovery could help astronomers better understand the environment around Sagittarius A*, a black hole with about four million times the Sun’s mass that lies roughly 26,000 light-years from Earth. Despite its enormous size, Sagittarius A* consumes relatively little material compared with some supermassive black holes in other galaxies.
A team led by Nicole Ford, a doctoral student at McGill University in Montreal, published the findings on Oct. 19 in The Astronomical Journal. The research builds on an earlier study published in May in The Astrophysical Journal.
In astronomy, the term “metals” refers to elements heavier than hydrogen and helium, including oxygen, iron and nickel. Stars produce these elements and release them into space through processes such as supernova explosions. By analyzing the chemical fingerprints of gas near Sagittarius A*, the researchers found a metal abundance that astronomers describe as “mildly supersolar.” The measurements provide new information about the black hole’s surroundings, although they do not by themselves explain why it consumes material so slowly.
What Webb found around the Milky Way black hole
Webb studied the central third of a light-year around Sagittarius A* using its Mid-Infrared Instrument, which splits infrared light — heat radiation that human eyes cannot see — into its component wavelengths so scientists can read the chemical fingerprints of gas clouds. The team observed the region in April and September 2024, focusing on a structure called the Minispiral, a three-armed pattern of warm gas that carries material toward the black hole from a cold ring farther out.
By measuring light from neon, argon, sulfur, nickel and iron, the researchers found that the metals most likely came from supernovas — the explosions of massive stars — that occurred near the black hole over time. The gas has a composition similar to that of many nearby stars, suggesting that the gas and stars formed together.
Some small, fast clumps of gas move toward Earth at more than 600 kilometers per second. Their glow suggests they pass through localized fast shocks, which are sudden collisions that heat and break apart dust. The paper also finds significant destruction of dust containing nickel and iron. Together, these details show a crowded, violent neighborhood where stars, explosions and radiation constantly reshape the black hole’s fuel supply.
How metal-rich gas could affect the black hole
Metals matter because they affect how quickly gas cools, and gas must cool and compress before it can flow toward a black hole. Metal-rich gas generally cools faster, which would normally accelerate the flow toward the black hole. The elevated metal abundance could therefore make Sagittarius A*’s relatively quiet behavior harder to explain.
Other reports point out, however, that 1.8 times the Sun’s metal abundance is relatively modest and probably cannot drive substantially faster cooling. They also suggest that continued heating from a nearby supernova remnant may help keep the inflow to a trickle. The researchers note that the gas’s behavior depends on local conditions, so astronomers cannot use its composition alone to determine how often the black hole has flared up in the past.
Even so, the measurements give computer models of the black hole’s feeding a more realistic starting point. Earlier simulations depended heavily on assumptions about the gas’s chemical composition. The team says the results could also help scientists understand how metals spread around distant supermassive black holes and how Earth acquired many of its own heavy elements.