Cosmic overcrowding constrains star formation, even in the early universe

RIVERSIDE, Calif., Aug. 24 (UPI) — Some of the most dense concentrations of star formation in the universe are found in massive star clusters encompassing hundreds of galaxies and trillions of stars. Yet, as new research points out, the more crowded a galaxy’s surroundings are, the more likely it is to stop producing new stars.

A new study, published this week in the journal Astronomy and Astrophysics, highlights this peculiar contradiction of the cosmos.

The effects of overcrowding are discernible as early as 10 billion years ago.

Recently, a group of astronomers from the United States and Chile were able to observe four of the most distant galactic clusters ever found. The clusters appear as they did just 4 billion years after the Big Bang.

The observations offer astronomers the earliest-yet look at how clusters influence galactic evolution and the trajectory of star formation.

“We looked at how the properties of galaxies in these clusters differed from galaxies found in more typical environments with fewer close neighbors,” Julie Nantais, an assistant professor at the Andres Bello University in Santiago, said in a news release.

“It has long been known that when a galaxy falls into a cluster, interactions with other cluster galaxies and with hot gas accelerate the shut off of its star formation relative to that of a similar galaxy in the field, in a process known as environmental quenching,” Nantais continued.

Researchers found that approximately 30 percent of the galaxies in the newly identified clusters are dormant. Older, closer clusters boast dormancy rates closer to 50 percent.

“While it had been fully expected that the percentage of cluster galaxies which had stopped forming stars would increase as the universe aged, this latest work quantifies the effect,” said Gillian Wilson, professor of physics and astronomy at the University of California, Riverside.

There are a number of mechanisms that can cause environmental quenching. One of the most common, researchers believe, is the influx of high energy particles and radiation which prevents galaxies from accreting cool gas, the most vital part of the star formation process.

Scientists say quantifying the rate of environmental quenching in the early universe is essential to the construction of cosmic evolution models. The latest research offers the best yet benchmark for that task.