Dense, Starless Cloud Cores Reveal Why Some Stars are Massive

Some stars can be massive while others remain more around the size of our own Sun or even smaller. Now, astronomers may have discovered exactly why some stars grow so large. Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, they've peered at the cores of some of the darkest, coldest and densest clouds in our galaxy.

Stars form at the hearts of these dark clouds, known as Infrared Dark Clouds. In this case, the astronomers spotted clouds located about 10,000 light-years away in the direction of the constellations of Aquila and Scutum. Since these cloud cores are so massive and dense, gravity should have already overwhelmed their supporting gas pressure and allowed them to form new, Sun-mass stars.

"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," said Jonathan Tan, one of the researchers, in a news release. "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."

So what exactly is this mechanism that can cause massive stars to form? The key to finding that out is to find examples of massive starless cores and to witness the very beginnings of massive star birth. In this case, the researchers examined the cloud cores for a unique chemical signature involving the isotope deuterium to take temperatures of the clouds and see if stars had formed. In the end, ALMA found that the cloud was both cold and starless.

In fact, it's very likely that some counter force is forestalling core collapse and buying enough time to form the massive star. It's very possible that strong magnetic fields may be propping up the cloud, preventing it from collapsing quickly.

"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," said Tan in a news release. "This may mean that nature is more important than nurture when it comes to determining a star's size."