Larger groups of newborn stars break free from their birth clouds faster than smaller ones, clearing away gas and filling galaxies with ultraviolet light, a new study shows.
The findings, published in Nature Astronomy, provide a more detailed understanding of star formation in galaxies, revealing how and where planets can form.
The process was extremely challenging to study anywhere beyond our Galaxy before the launch of the James Webb Space Telescope (JWST) and the Hubble Space Telescope (HST).
Now, an international team has used these observatories to look in detail at thousands of young star clusters in four nearby galaxies at different stages of their evolution.
The unique capabilities onboard JWST and HST reveal the most massive clusters fully emerge and disperse surrounding clouds of gas after around five million years, while less massive clusters were between seven and eight million years old before they left their nurseries behind.
"Stars are formed inside the densest, coldest and most obscure regions inside large interstellar clouds made up of gas and tiny dust particles," explains Dr Ana Duarte Cabral, Royal Society University Research Fellow at Cardiff University and one of the study's co-authors.
"Unfortunately, this means we cannot see the process of star formation using optical light, as those tiny dust particles block the visible light – a bit like a cloud of smoke – and all we can see is the silhouette of the parent clouds, but not the little star-embryos forming inside it.
"Luckily, when we look at those regions using infrared light, we can see through the clouds and see the regions that are being heated up by the forming stars shinning bright, effectively letting us see the new generation of stars as they are still embedded in their natal clouds.
"This has been long used to study star formation in our own Galaxy, the Milky Way, in great detail, but we were missing the ability to study systematically how this process occurs across galaxies.
"With the advent of JWST, which traces the infrared light with unprecedented resolution and sensitivity, this is now finally changing."
The team pored over images of four nearby galaxies — Messier 51, Messier 83, NGC 628, and NGC 4449 — from the FEAST observing programme (#1783), identifying nearly 9,000 star clusters in different evolutionary stages.
With JWST's ability to peer inside the gas clouds, they were able to estimate the mass and age of each cluster.
By combining these data with HST data, which traces the optical and ultraviolet light, we can start to measure how long it takes these stellar clusters to clear out their surrounding natal cloud.
Massive star clusters, with their large numbers of hot high-mass stars, naturally emit most of the ultraviolet light in galaxies, but this work confirms that they also get a head start on producing stellar feedback over lighter clusters.
Knowing where and when this stellar feedback is strongest throughout the lifetime of a galaxy allows astronomers to better predict how star-forming fuel is pushed around the galaxy and therefore how stars, and star clusters, are likely to form.
"Simulations of star formation and stellar feedback have struggled to reproduce how star clusters form and emerge from their natal clouds. These results give us important new constraints on that process," explained Dr Angela Adamo of Stockholm University and the Oskar Klein Centre in Sweden, a lead author on the study and principal investigator on the FEAST programme.
Theories of how planets form are also impacted by the team's research.
The faster gas is cleared away within a star cluster, the earlier protoplanetary discs around stars are exposed to harsh ultraviolet radiation from other stars, giving them less opportunity to attract further gas from the nebula.
This reduces the opportunities they have to grow dust and create planets.
"This work brings together researchers simulating star formation and those working with observations, as well as groups researching planet formation," said Alex Pedrini, lead author, of Stockholm University and the Oskar Klein Centre in Sweden.
"Using Webb, we can look into the cradles of star clusters and connect planet formation to the cycle of star formation and stellar feedback."
