Illustration courtesy David A. Hardy, AstroArt/U. Manchester
Published July 11, 2013
Astronomers announced this week that they may have discovered the largest baby star ever detected, nestled within a stellar nursery 10,000 light-years away.
The embryonic stellar monster, known as a protostar, sits at the center of a whirling dark cloud with tentacles of gas and dust. The cloud —which is 500 times the mass of our sun — is the largest ever seen in our galaxy.
"We have discovered the most massive protostar known in our galaxy and a beautiful network of filaments funneling even more matter onto it," said Gary Fuller, the study's co-author and an astronomer at the University of Manchester in England.
"Only about 1 in 10,000 stars is as massive as the one we are seeing forming."
Using radio observations obtained from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the nascent star has been caught in the act of still forming — gobbling up its surrounding cloud of gas and dust known as the Spitzer Dark Cloud (SDC) 335.579-0.292. The SDC was named after the NASA infrared space telescope that first spotted it.
Fuller suspects that because the protostar is still feeding, it is continuing to grow as it gathers mass from the cloud.
"It's surprising that we managed to find such an extreme and rare object with some of the very first observations made with ALMA, at the same time revealing the complex nest of filaments which are feeding this baby monster," he said.
At some point in the distant future, the surrounding cloud is expected to completely collapse in on the star, making it more than a million times brighter than our sun, says Fuller.
However, because the star is still in the early stages of its life, astronomers can only make an educated guess about its final mass. Comparisons with recently discovered record-breaking mature stars indicate that it may end up at least 200 to 300 times the mass of the sun when it is fully formed. (Related: "Most Massive Star Discovered—Shatters Record.")
Fast and Furious
But astronomically at least, the wait won't be long, especially when compared with the lifetimes of dwarf stars like our sun, which are measured in billions of years. Massive objects like the one forming live fast and die young in huge stellar explosions, says Fuller.
"It will take only about 100,000 years for the star to grow to its final mass, and by then it will have cleared away the remaining dust and gas around itself and become visible at optical wavelengths," said Fuller. "After less than a million years, it will then die as a spectacular supernova."
While this newfound star-forming region is the largest yet, some in the astronomy community caution against jumping to the conclusion that this may be the birth of a true record-breaking stellar giant.
"What the study team saw is a dense cloud of gas that they think, probably correctly, is going to collapse to form a massive star at some point in the future; however, one or more small stars are hidden behind the huge amount of dust in the cloud, and thus there is no way of measuring their present masses," said astronomer Mark Krumholz of the University of California, Santa Cruz, who is not connected with the study.
In other words, with so much obscuring dust there would be no way to measure the forming star's current weight nor predict its final mass, so the 500 solar masses observed is actually the mass of the cloud, not the mass of the star itself.
"While it is likely that there will be one or more that end up significantly more massive than the sun, there is no good reason to believe that any of the stars formed in this cloud are, or will be, the most massive in the Milky Way," explained Krumholz.
Regardless of who holds the heavyweight title, supermassive stars like the one growing in this distant cloud are known to play a key role in peppering the cosmos with the basic building blocks for solar systems like ours.
Current theories hold that our sun's empire was born about five billion years ago from the ashes of an ancient supernova explosion.
"Without such massive stars, there wouldn't be heavy elements in the universe," said Fuller.
"The supernova which marks the death of a massive star seeds the galaxy with the heavy elements that eventually form rocky planets like the Earth, and are essential for life."
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