It’s hard for astronomers to understand how stars 10 times as massive as the Sun, or more, can exist, because as they grow, they tend to push away the gas they feed on, starving their own growth. Now researchers suggest that newly-formed stars may grow to great mass if they form within a group of older stars, if these surrounding stars are favorably arranged to confine and feed gas to the younger ones. The astronomers have seen evidence of this collective feeding, which they label “convergent constructive feedback”, in a giant cloud of gas and dust – Westerhout 3 (W3) – located 6,500 light years from us.
To study the formation of high-mass stars, Alana Rivera-Ingraham and collaborators used far-infrared images from the European Space Agency’s Herschel Space Observatory. Regions of the gas cloud where stars are about to form can be found by mapping the density of dust and its temperature, looking for the most dense regions where the dust is shielded and cold.
Stars are born in the denser parts of gas clouds, where the gas gets compressed enough by gravity to trigger nuclear fusion. The more massive the newborn star, the more visible and ultraviolet light it emits, heating up its surroundings — including the dust studied by Herschel. However, “The radiation during the birth of high-mass stars is so intense that it tends to destroy and push away the material from which they need to feed for further growth,” explained Rivera-Ingraham. Scientists have modeled this process and found that stars about eight times the mass of our Sun would stop growing because they run out of gas. Yet astronomers do see stars that are more massive than this theoretical limit.
The researchers noticed that the densest region of the cloud was surrounded by a group of old high-mass stars. Previous generations of large stars may enable the next ones to grow also massive, and close to each other. Like young high-mass stars, older stars also radiate and push gas away. If such older stars happen to be arranged favorably around a major reservoir of gas, they can compress it enough to ignite new stars. This corralling of dense gas can give birth to new, high-mass stars. A large newborn star will push its food source away, but if it is surrounded by enough large stars, these can keep nudging gas back at it.
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