July 11, 2013
Monstrous Stellar Collisions Not Expected To Occur Anytime Soon
Lee Rannals for redOrbit.com - Your Universe Online
Astrophysicists from the Astronomical Observatory of the Faculty of Physics at the University of Warsaw say the next collision of monstrous stars will not occur until billions of years from now.
Three years ago, scientists discovered that the Magellanic Clouds host gigantic stars with between 200 and 300 times the solar massÂ of our own Sun. Before then, astronomers believed that the biggest stars in the Universe did not exceed 150 solar masses. This discovery made astrophysicists wonder what would happen if these behemoth stars collided.
Astronomers theorized that the gravitational waves resulting from such a collision would be powerful enough that even our current detectors could sense them, even at distances much larger than for typical stellar black holes.
"But we cannot count on detecting any such spectacular collision," says Dr. Krzysztof Belczynski of the Astronomical Observatory of the Faculty of Physics at the University of Warsaw.
Scientists used computer modeling to demonstrate that some super-massive stars could form black holes. The universe might play host to binary systems of super-massive stars which later evolve or transform into systems of two black holes with masses much larger than typical black holes.
Objects orbiting in a tight binary system composed of neutron stars or ordinary black holes lose their energy over time, which leads them to closer and closer orbits, eventually causing a collision. The collision of black holes produced by super-massive stars would create gravitational waves strong enough that they might be detected in the near future. However, a collision like this is not taking place any time soon.
"We know that the components of such a system must be formed at a relatively large distance from each other. We also know that super-massive stars do not expand, so there cannot be a common envelope phase. This means that there is no physical mechanism that would effectively cause the orbit to tighten," said Belczynski.
The only process that allows for a gradual loss of energy by the remnants of super-massive stars in a binary system is the emission of gravitational waves. The gravitational waves emitted by such a system of widely separated stars or black holes are weak and the energy loss is slow.
"It will take many tens of billions of years, perhaps hundreds of billions of years, for the black holes to collide. That is many times longer than the amount of time which has passed since the Big Bang, so we stand practically no chance of detecting the gravitational waves from such a collision in the heavens," said Dr. Daniel Holz of the University of Chicago.
The scientists say that unless the current models of stellar evolution and the formation of binary stars in dust clouds of matter are wrong, then the observation of such a collision is not feasible for years to come.