The supermassive black hole at the center of the Milky Way is surrounded by an unexpected trove of heavy metals, according to new observations by the James Webb Space Telescope (JWST). The discovery may offer new clues about how Earth acquired its share of heavy elements, but it could also make one of the most enduring mysteries about our galaxy’s central black hole even harder to solve.
In astronomy, the term “metals” refers to any elements heavier than hydrogen or helium. Common examples include oxygen, carbon, iron, and gold. These elements are forged through nuclear fusion in the dying stars and are then ejected into space before being incorporated into new generations of stars.
Scientists say the material detected by JWST likely came from supernovas — stellar explosions that blasted the metals into the region around Sagittarius A* (Sgr A*), the supermassive black hole at the heart of our galaxy.
The metals, detected as gas, appear to have the same composition as several nearby stars, suggesting that both the stars and the gas may have originated at roughly the same time. The researchers published the observations in a paper on Oct. 19 in The Astronomical Journal, following up on earlier work published in The Astrophysical Journal in May.
“We know there is a black hole at the centre 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,” said Nicole Ford, first author of the new paper and a doctoral student in astrophysics at McGill University in Montreal, in a statement. “Part of understanding why this is happening means looking at the properties of the materials available for it to consume, including gas, dust and the stars orbiting around it.”
JWST orbits at Lagrange point 2, about 1 million miles (1.5 million kilometers) from Earth in the direction opposite the Sun. The telescope identified the heat signatures of specific gas clouds near the black hole, as well as the metal content within those clouds.
These findings could advance understanding of how metals are distributed around supermassive black holes in more distant galaxies, as well as the processes that supplied Earth with many of these elements, the researchers said. The metals’ presence influences how quickly gases cool, which in turn influences how readily the gas can be drawn into a black hole, they added.
The previous study in The Astrophysical Journal indicated that gas emissions near the black hole had been influenced by conditions in the local clouds. The researchers noted, however, that this means the gas alone cannot serve as a proxy for how often the black hole has been active.