Evrim Yazgin
Cosmos science journalist
NASA’s James Webb Space Telescope has identified a black hole that confirms the theory that some supermassive black holes can starve their host galaxies of the fuel needed to make new stars.
GS-10578, nicknamed “Pablo’s Galaxy”, is roughly the size of the Milky Way. It is nearly 12 billion light-years away, meaning the light that has reached Earth is from a time when the universe was only about 2 billion years old, roughly 15% of its current age.
It is massive for such an early galaxy. The total mass of Pablo’s Galaxy is about 200 billion times the mass of our Sun.
The detailed study of the galaxy is published in the journal Nature Astronomy.
“Based on earlier observations, we knew this galaxy was in a quenched state: it’s not forming many stars given its size, and we expect there is a link between the black hole and the end of star formation,” says co-lead author Francesco D’Eugenio from the University of Cambridge Kavli Institute for Cosmology.
“However, until Webb, we haven’t been able to study this galaxy in enough detail to confirm that link, and we haven’t known whether this quenched state is temporary or permanent,” D’Eugenio adds.
Most of the stars in Pablo’s Galaxy were formed 12.5–11.5 billion years ago.
“Dead galaxies” are those which, like Pablo’s Galaxy, have used up all their fuel and are no longer producing new stars. Minor mergers and accretion of nearby gas can cause such galaxies to “puff up”, but they are not able to rejuvenate their earlier rates of star production.
The same team which published the new study of Pablo’s Galaxy was behind the discovery earlier this year of the oldest dead galaxy, JADES-GS-z7-01-QU, which stopped producing stars about 13 billion years ago, only 700 million years after the Big Bang.
Pablo’s Galaxy is also relatively old.
“In the early universe, most galaxies are forming lots of stars, so it’s interesting to see such a massive dead galaxy at this period in time,” says co-author Roberto Maiolino, also from the Kavli Institute. “If it had enough time to get to this massive size, whatever process that stopped star formation likely happened relatively quickly.”
Webb’s data showed Pablo’s Galaxy is expelling large amounts of gas at about 1,000 km/second. This is fast enough for the gas to escape the galaxy’s gravitational pull.
Like other galaxies with supermassive black holes, Pablo’s Galaxy has fast outflowing winds of hot gas. But the mass of this gas is small.
Earlier telescopes could not see what Webb can – a colder wind component which is denser and doesn’t emit any light. The mass of this cold gas which is ejected out of the galaxy is much greater than what the galaxy requires to keep forming new stars.
“We found the culprit,” says D’Eugenio. “The black hole is killing this galaxy and keeping it dormant, by cutting off the source of ‘food’ the galaxy needs to form new stars.”
The discovery proves what astrophysicists have predicted.
“We knew that black holes have a massive impact on galaxies, and perhaps it’s common that they stop star formation, but until Webb, we weren’t able to directly confirm this,” says Maiolino. “It’s yet another way that Webb is such a giant leap forward in terms of our ability to study the early universe and how it evolved.”
