December 21, 2013
Researchers Discover Possible Causes Of Massive Star Formation
redOrbit Staff & Wire Reports - Your Universe Online
In an attempt to determine why massive stars – those with at least eight times the mass of our Sun – grow so much larger than most other stars in our galaxy, astronomers used the ALMA telescope to examine the cores of Infrared Dark Clouds roughly 10,000 light-years away.
Since these clouds are so massive and dense, the researchers said gravity should have already overwhelmed their supporting gas pressure, making it possible for them to collapse and form new Sun-mass stars. If a star had not yet started shining, that would serve as a tip-off that the cloud was being supported by something else.
“A starless core would indicate that some force was balancing out the pull of gravity, regulating star formation, and allowing vast amounts of material to accumulate in a scaled-up version of the way our own Sun formed,” lead author and University of Florida, Gainesville astrophysicist Jonathan Tan explained in a statement Friday. “This suggests that massive stars and Sun-like stars follow a universal mechanism for star formation. The only difference is the size of their parent clouds.”
According to Tan and his colleagues, average stars like our sun start off their lifespan as dense, low-mass concentrations of hydrogen, helium and other trace elements inside large molecular clouds. Once the initial kernel emerges from the surrounding gas, gravity causes material to collapse into the central region through a swirling accretion disk. Eventually, planets form, nuclear fusion begins at the core, and a star is formed.
The formation of the overwhelming majority of stars in our galaxy can be explained using this model, but Tan said some additional force needs to be accounted for in order to explain the formation of more massive stars. This force must balance out the normal process of collapse, he said, and some have speculated there must be two individual models of star birth – one that accounts for regular stars, and one that accounts for massive stars.
To figure out the answer, the researchers set out to find examples of massive starless cores in order to observe the first stages of massive star formation. As the international team explained in the latest edition of The Astrophysical Journal, they used ALMA in order to look within these cores in search of a unique chemical signature that included the isotope deuterium.
Hunting for this isotope essentially allowed them to gauge the temperature of these clouds and determine whether or not stars had formed within them. Deuterium is said to be important as it often bonds with certain molecules under cold conditions. Once it starts to form and heat the surrounding gas, it is replaced with a more common hydrogen isotope.
Tan’s team detected a considerable amount of deuterium in the cloud, which suggests it is cold and starless – likely meaning some other force (possibly a strong magnetic field) is delaying core collapse and buying additional time for a massive star to begin forming.
“These new ALMA observations reveal objects that are quite similar to the nurseries of Sun-like stars, but simply scaled-up by tens or a hundred times. This may mean that nature is more important than nurture when it comes to determining a star’s size,” he concluded.