Webb telescope shows features of the oldest massive and dense galaxy

GS-9209 observed by the James Webb Space Telescope along with other galaxies. G. BRAMMER, C. WILLIAMS, A. CARNALL

Despite being about 10 times smaller than the Milky Way, GS-9209 has a similar number of stars to our own galaxy.

Observations with the Webb Space Telescope have revealed a massive and dense galaxy formed between 600 and 800 million years after the Big Bang, the oldest of its kind found so far. Despite being about 10 times smaller than the Milky Way, GS-9209 has a similar number of stars to our own galaxy, according to a team led by Edinburgh researchers.

These have a combined mass of about 40 billion times that of our Sun, and formed rapidly before star formation in GS-9209 stopped, says the study, published in Nature.

GS-9209 is the first known example of a galaxy that is no longer forming stars, known as a quiescent galaxy. When the team observed it 1.25 billion years after the Big Bang, no stars had formed in the galaxy for about 500 million years. The analysis also shows that GS-9209 contains a supermassive black hole at its center that is five times larger than astronomers might anticipate in a galaxy with this many stars. The discovery could explain why GS-9209 stopped forming new stars, the team says.

The growth of supermassive black holes releases enormous amounts of high-energy radiation, which can heat up and push gas out of galaxies. This could have caused star formation to halt in GS-9209, as stars form when clouds of dust and gas particles within galaxies collapse under their own weight.

GS-9209 was first discovered in 2004 by University of Edinburgh PhD student Karina Caputi, who was supervised at the time by Professors Jim Dunlop and Ross McLure in the University’s School of Physics and Astronomy. Caputi is now a professor at the University of Groningen, the Netherlands. “The James Webb Space Telescope has already shown that galaxies grew larger and earlier than we suspected during the first billion years of cosmic history. This work gives us our first really detailed look at the properties of these first galaxies, mapping in detail the story of GS-9209, which managed to form as many stars as our own Milky Way in just 800 million years after the Big Bang.The fact that we also see a very massive black hole in this galaxy was a big surprise, and lends a lot of weight to the idea that these black holes are what shut down star formation in the first galaxies,” says Dr Adam Carnall, from the University of Edinburgh’s School of Physics and Astronomy.

source: https://www.nature.com/articles/s41586-023-06158-6