When Massive Stars Collide, Monsters Are Formed
August 7, 2012

Astronomers Crack The Code Of Mysterious Monster Stars

Lee Rannals for redOrbit.com - Your Universe Online

Astronomers now believe the "monster stars" located in the nearby galaxy the Large Magellanic Cloud (LMC) were formed through the merger of lighter stars.

The team wrote in the journal Monthly Notices of the Royal Astronomical Society that the group of stars may have formed while smaller stars were in a tight binary system.

In 2010, scientists discovered these supermassive stars, one of which is more than 300 times the mass of the Sun. These objects have never been found anywhere else in the universe, so far.

The galaxy the stars reside in sits 160,000 light years away from Earth, and is the third nearest satellite of the Milky Way galaxy.

LMC has many star forming regions, with the most active being the 1,000 light-year diameter "Tarantula Nebula," where the four supermassive stars can be found.

Until astronomers found the monster stars, they believed the stars with the largest mass were about 150 times the mass of the Sun.

"Not only the upper mass limit but the whole mass ingredient of any newborn assembly of stars appears identical irrespective of the stellar birthplace", Prof. Dr Pavel Kroupa of the University of Bonn, a co-author on the new paper, said. "The star birth process seems to be universal".

The team modeled the interactions taking place between the stars located in the Tarantula Nebula. They assembled the model cluster star by star, to resemble the real cluster as closely as possible. This created a cluster of over 170,000 stars packed tightly together.

To compute how even this basic system changes over time, the model had to solve 510,000 equations many times over. This simulation, complicated by the effect of the nuclear reactions, lead to energy being released by each star, making stars collide.

The star-by-star calculations known as "direct N-body simulations" are the most reliable and accurate way to model clusters of stars.

"With all these ingredients, our R136 models are the most difficult and intensive N-body calculations ever made", the team wrote in a statement regarding their study.

Dr. Sambaran Banerjee said that once these calculations were done, it became clear that the stars were no mystery.

"They start appearing very early in the life of the cluster," Banerjee said. "With so many massive stars in tight binary pairs, themselves packed closely together, there are frequent random encounters, some of which result in collisions where two stars coalesce into heavier objects."

He said imagine two stars closely circling each other, but as they are stretched by the gravitational attraction from their neighboring stars, they smash into each other as they pass and make a single supermassive star.

"Although extremely complicated physics is involved when two very massive stars collide, we still find it quite convincing that this explains the monster stars seen in the Tarantula", Banerjee said in the release.