The Most Distant Galactic Gas Outflow Has Been Observed By Astronomers

Artist's impression of an outflow of gas from a star-forming galaxy. NRAO/AUI/NSF, D. Berry

The evolution of galaxies, especially in the early universe, is marked by intense periods of star formation interspersed with times when the birth of new stars is snuffed out. This growth regulation is often carried out by huge galactic winds, and researchers have just found the most distant yet.

Using the extraordinary capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA), researchers have measured the speed of a galactic wind in galaxy SPT2319-55. This record observation shows this phenomenon taking place when the universe was just 1 billion years old. The findings are reported in Science.

The observations were possible thanks to a gravitational lens. The light from SPT2319-55 was magnified by the space-time distortion created by a massive foreground galaxy. ALMA detected the molecule hydroxyl (OH) and measured the wind's speed to be 800 kilometers (500 miles) per second.

This suggests that the wind takes away as much gas as is being converted into stars, an efficient way to quench star formation. However, the team thinks that only one-tenth of the wind will truly escape the galaxy. The rest will fall back in due to gravity and condense into a subsequent generation of stars.

The image of the outflow, or "wind", from a galaxy seen when the universe was only 1 billion years old. ALMA (ESO/NAOJ/NRAO), Spilker; NRAO/AUI/NSF, S. Dagnello; AURA/NSF

“Galaxies are complicated, messy beasts, and we think outflows and winds are critical pieces to how they form and evolve, regulating their ability to grow,” lead author Justin Spilker, from the University of Texas at Austin, said in a statement. “So far, we have only observed one galaxy at such a remarkable cosmic distance, but we’d like to know if winds like these are also present in other galaxies to see just how common they are. If they occur in basically every galaxy, we know that molecular winds are both ubiquitous and also a really common way for galaxies to self-regulate their growth.”

Galactic winds are a powerful feedback mechanism during periods of increased star formation. They are caused either by repeated supernova explosions, as the most massive of these new stars end their lives pretty quickly (in cosmic terms), or by eruptions from the central black hole if it receives enough in-falling gas.

The early universe remains a mysterious but fundamental time for helping us understand the evolution of galaxies. The new observations, along with additional ones by ALMA and other telescopes, are finally opening a window into this epoch.


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