December 4, 2013
Explosive Milky Way Protostar Reveals Details About Star Formation
Brett Smith for redOrbit.com - Your Universe Online
Using the Atacama Large Millimeter Array (ALMA) telescope in northern Chile, scientists have identified a very young star in our galaxy which had such an explosive birth, it used to be about 100 times brighter than it is now, according to a new study in Astrophysical Journal Letters.
The study, from astrophysicists at the Niels Bohr Institute and the Centre for Star and Planet Formation at the University of Copenhagen in Denmark, has revealed some new details about the mechanics behind star formation.
"We studied the chemistry of the gas and dust cloud surrounding the early protostar (an early stage of star formation),” explained study author Jes Jørgensen, an associate professor of astrophysics at the Niels Bohr Institute.
Stars form when a large cloud of gas and dust collects and becomes so dense that it collapses into a ball. The pressure within this dense cluster heats condensed gas and dust, leading to the creation of a glowing ball of light.
“In this dense cloud, a chemical reaction takes place that enables the formation of several kinds of complex molecules, including methanol,” Jørgensen said. “One would expect that all of the molecules would be near the star, but with one of them we saw a clear ring structure. Something had removed a certain molecule, HCO+, from a wide area around the protostar.”
HCO+ is an important signifier molecule in star formation because it is particularly sensitive to water vapor, which can quickly dissolve the molecule. The nonexistence of HCO+ molecule can be used to learn the process behind star formation, Jørgensen said.
At the start of the star formation process, the raw materials of gas and dust are extremely cold. Eventually, simple molecules such as carbon monoxide and water aggregate on the grains of dust and freeze into ice. When these simple molecules become close to each other, they react to form more complex molecules like methanol, ethanol, and simple sugars. As the gravity of the early protostar draws together the surrounding gas and dust cloud, it slows these raw materials down and the energy released by this slowing is converted into heat. This heat melts any ice, which turns into water vapor.
"From the area where the HCO+ molecule has been dissolved by water vapor we can now calculate how bright the young star has been,” Jørgensen explained. “It turns out that that the area is much greater than expected compared to the star's current brightness. The protostar has been up 100 times brighter than the star is now. From the chemistry we can also say that this change happened within the last 100-1000 years – that is to say, very recently from an astronomical point of view.”
The Danish astrophysicist said several bursts of light and heat radiation probably occurred during the formation process.
"One of the major questions if we take a long view, is whether this is a common phenomenon – whether all young stars undergo similar 'eruptions' and if so, how often," Jørgensen said.