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| Space on Aug 27, 2012

How big is the biggest monster star?

The most massive star known is more than 300 times more massive than our sun – twice as massive as what astronomers thought was possible.

One of the great mysteries of astronomy has been super-sized stars. How big can stars get? And how do these monster stars get so big? In the year 2010, scientists discovered four monster stars in the Large Magellanic Cloud. That’s a nearby dwarf galaxy – 160 thousand light-years away. The heaviest is more than 300 times more massive than our sun by some estimates – twice as massive as what astronomers thought was possible. This star is known to astronomers as R136a1. It is the most massive star known at this time (August 2012) and is also the most luminous star known at more than 8 million times the luminosity of our sun.

Relative sizes of young stars, from the smallest red dwarfs (far left), weighing in at about 0.1 solar masses, through low-mass yellow dwarfs such as our sun, to massive blue dwarf stars weighing eight times more than our sun, to the 300-solar-mass monster star named R136a1, the most massive star known. Image credit: Wikipedia.

R136a1 is what’s known as a Wolf–Rayet star. Its surface temperature is over 90,000 degrees F. Like other extremely large stars, R136a1 has been shedding a large fraction of its initial mass through a continuous stellar wind. In other words, it was even more massive when it first formed and is estimated to have lost 50 solar masses over the past million years.

Yet, for decades, theories have suggested that no stars can be born by ordinary processes above 150 solar masses. So how did R136a1 and stars like it grow so large? And why aren’t monster stars scattered throughout space? Recently, astronomers have begun to suggest that supermassive stars like this one form through mergers of multiple stars. In 2012, astronomers at the University of Bonn suggested the the ultramassive stars in the Large Magellanic Cloud – such as R136a1 – were created lighter stars in tight double-star systems merged.

List of most massive stars

An image of the Wolf-Rayet star R136a1, the most massive star known. Image credit: Wikipedia.

Still, double-star systems are common. So why don’t we see more super-sized stars? The astronomers in Bonn say it’s because these stars formed under special conditions – in a densely packed star cluster. In a closely packed star cluster, double-stars are more likely to encounter each other and merge.

But if these ultramassive stars form in this way, why don’t we see more of them? After all, multiple star systems are common throughout space, while monster stars are few and far between. The answer is probably that monster stars don’t live very long. They end their lives as violent supernova explosions.

Bottom line: Astronomers have said for decades that no star can be born by ordinary processes with more than 150 times our sun’s mass. And yet more massive stars are known. The most massive star known is R136a1, in the Large Magellanic Cloud. It’s thought to be more than 300 times more massive than our sun, by some estimates. In 2012, astronomers at the University of Bonn suggested that such a star could form by the merger of multiple star systems, in a densely packed star cluster.