If it took our Sun’s place, it would outshine our star by as much as the Sun currently outshines the full Moon, scientists said. “It would bathe the Earth in incredibly intense ultraviolet radiation,” shutting off any chance of life, said Raphael Hirschi from Keele University, U.K., a member of the research team.
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| The star cluster RMC 136a in three increasingly close-up views from top to bottom. (Courtesy ESO) |
The first, designated NGC 3603, is a cosmic factory where stars form frantically out of extended clouds of gas and dust. The second, known as R136, is another cluster of young, massive and hot stars, located in zone called the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud.
The two clusters lie 22,000 and 165,000 light-years away, respectively. A light-year is the distance light travels in a year.
The researchers found several stars with estimated surface temperatures over 40,000 degrees Celsius, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter.
Theoretical models imply that several of these stars were born with masses over 150 solar masses, investigators explained. One found in the closer cluster is the heaviest, currently weighing in at about 265 solar masses and with an estimated birthweight of up to 320.
Not only is that star the most massive ever found, it’s also the brightest, almost 10 million times more luminous than the Sun. “Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon,” said Crowther.
Giant stars produce powerful outflows that make them shrink as they give up some of their contents to space. “Unlike humans, these stars are born heavy and lose weight as they age,” said Crowther. “Being a little over a million years old, the most extreme star, R136a1, is already ‘middle-aged’ and has undergone an intense weight loss programme, shedding a fifth of its initial mass.”
These monstrous stars form only in the most closely packed star clusters, members of the research team said. They added that distinguishing the individual stars, a new achievement, required the exquisite resolving power of the infrared light instruments on the Very Large Telescope in Paranal, Chile.
The team also estimated the maximum possible mass for the stars within these clusters and the relative number of the most massive ones. “The smallest stars are limited to more than about eighty times more than Jupiter, below which they are ‘failed stars’ or brown dwarfs,” said team member Olivier Schnurr from the Astrophysikalisches Institut Potsdam in Germany.
“Our new finding supports the previous view that there is also an upper limit to how big stars can get, although it raises the limit by a factor of two, to about 300 solar masses.”
Within R136, only four stars weighed more than 150 solar masses at birth, yet they account for nearly half of the wind and radiation power of the whole cluster, about 100,000 stars in all, according to astronomers. R136a1 alone energises its surroundings by more than a factor of fifty compared to the Orion Nebula cluster, the closest region of massive star formation to Earth.
Understanding how high mass stars form was already puzzling, researchers said, so that the identification of such extreme cases raises the challenge to theorists still further. “Either they were born so big or smaller stars merged together to produce them,” said Crowther.
The findings are described in the research journal Monthly Notices of the Royal Astronomical Society.
Stars between about eight and 150 solar masses explode at the end of their short lives as so-called supernovas, leaving behind exotic remnants known as either neutron stars or black holes. The new findings raise the prospect of the existence of exceptionally bright supernovas that totally blow themselves apart, leaving no remnant and dispersing up to ten solar masses of iron into their surroundings, according to researchers. Such explosions may have already been detected in the past, they added, with a few candidate events ripe for further investigation.
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