Stars vary from tiny and red to gigantic and blue. While small stars are abundant in the Milky Way, massive ones at least eight times the Sun’s mass are rare. Scientists have long wondered how huge stars grow to such proportions.
An article (The Astrophysical Journal) proposes that magnetic fields inside certain star-forming regions stall the gas clouds’ collapse, allowing stellar embryos to gestate for longer periods before they move on to their next phase of development.
Stars like the Sun form in the cores of molecular clouds. Parts of the cores collapse under their own gravity, forming kernels that then attract more gas. Eventually, the kernels grow massive and hot enough to
begin fusion. But if massive stars also form this way, why don’t the clouds always collapse at similar points, forming kernels and thus future stars of similar sizes?
A research team led by Jonathan Tan of the University of Florida in Gainesville set out looking for “starless cores” dense regions of gas through which no starlight yet shines. “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”, says Tan.
Tan’s team found what they were looking for, using the Atacama Large Millimeter submillimeter Array (ALMA) to take
the temperatures of massive molecular clouds and determine whether young stars had heated the gas. They had not, which means an outward-pressing force is keeping the cores from collapsing and giving the gas kernels time to grow larger. The astronomers think magnetic field lines may prop the cloud up, balancing the gravitational urge, at least for a while.
Why did Mars go cold and dry?
Despite abundant evidence of a warm, wet Mars in the distant past, the first billion or so years of the planet’s existence, the Red Planet is now cold and dry — a desert. So where did all the water go?
Evidence of water exists in many places, including in the sulfate rocks examined by several martian rovers and in evidence for ice in various places around the planet (and below its surface).
Water-eroded valleys, gullies, branching valley networks, layered deposits (possibly from onceexisting lakes), and outflow channels extending from the ends of canyons all provide more reasons scientists believe that water/liquid flowed on the martian surface.
The reason why Mars was warm and wet early on, and why it transformed some 3 billion or more years ago, remains elusive. But the answers may hold important lessons for our own planet.