Ancient galaxies recycle gas from old stars into new ones

2023-06-01 13:28:59

Conceptual image of an ancient massive galaxy that recycles gas to sustain its growth. The background is an image of the Subaru and Keck telescopes. – TSINGHUA UNIVERSITY/NAOJ

MADRID, 1 Jun. (EUROPA PRESS) –

New observations show that ancient galaxies they were able to recycle gas from earlier stars into new generations of stars.

This recycled gas could have been enough to supply all the material needed for continued star formation. This discovery sheds new light on the evolution of galaxies and stars.

The gas provides the material for galaxies to form new stars. When stars die in supernovae explosions, they can eject gas out of the galaxy. So continued star formation requires a supply of gas that falls into the galaxy. But it has not been clear whether star formation is driven by a supply of pristine new gas or whether galaxies they can recycle gas from previous generations of supernovae.

To answer this question, an international team of researchers led by Tsinghua University observed a galaxy that existed 11 billion years ago. The pristine gas will consist mostly of hydrogen, with some helium. On the other hand, the recycled gas will contain heavier elements produced by nuclear fusion in stars.

In data from the Keck II telescope and the Subaru telescope, the team detected signs of hydrogen, helium and carbon extending up to 300,000 light-years around the galaxy. The proportions of the elements are similar to those seen on the Sun, which is surprising. for a galaxy so old that it would be expected to be closer to the pristine state of the new gas.

The team was also able to map the movement of the gas. Comparison with models shows that heavy element-enriched gas is returning to the galaxy, delivering some 700 times the mass of the Sun in recycled gas each year. This is far more than is needed to fuel the observed star formation rate in the galaxy, some 81 times the mass of the Sun each year, indicating that gas recycling alone is sufficient to drive the star formation in the galaxy.

Research team leader Zheng Cai, associate professor at Tsinghua University, comments it’s a statement on the role of the Subaru Telescope in this project: “The Subaru Telescope played a very important role in obtaining hydrogen emissions to measure the ratio between hydrogen and the heavier elements.”