First stars in the Universe might have been “dark stars” with no twinkle

December 3rd, 2007 - 1:07 pm ICT by admin  

Washington, Dec 3 (ANI): The first stars in the beginning of the universe might have been invisible “dark stars”, which were powered by the presence of dark matter, a new study has indicated.
A dark star is a theoretical object under Newtonian mechanics that, due to its large mass, has a surface escape velocity that equals or exceeds the speed of light. Any light emitted at the surface of a dark star would thus be trapped by the star’s gravity rendering it dark, hence the name.
Such objects in modern understanding would be more properly described as black holes.
The new study, which point to these objects as being the first stars in the universe, was conducted by astrophysicist Paolo Gondolo, associate professor of physics at the University of Utah.
It was also calculated by the study that how the birth of the first stars almost 13 billion years ago might have been influenced by the presence of dark matter, which is the unseen, yet-unidentified stuff that scientists believe makes up most matter in the universe and is even helping it to expand further.
Scientists generally believe that the universe came into being 13 billion years ago in a sudden expansion or “inflation” of time and space known as the “big bang.”
The afterglow of that explosion, known as the cosmic microwave background radiation, developed small fluctuations in temperature that caused some of the earliest matter to begin clumping together, a process accelerated by gravity and that produced the first stars and galaxies. The matter was mostly dark matter but also included normal matter in the form of hydrogen and helium gas.
Scientists know dark matter exists because galaxies rotate faster than can be explained by the visible matter within them. Also, observations by satellites, balloons and telescopes have led to the estimate that all the visible matter represents only 4 percent of the universe, which also is made of 23 percent dark matter and 73 percent “dark energy”.
For the new study about the “dark stars”, the astrophysicists calculated how dark matter would have affected the temperature and density of gas that clumped together to form the first stars.
The findings suggest that dark matter neutralinos interacted so they “annihilated” each other, producing subatomic particles called quarks and their antimatter counterparts, antiquarks. That generated heat. As a proto-stellar cloud of hydrogen and helium tried to cool and shrink, the dark matter would keep it hot and large, preventing fusion from igniting the star.
“The heating can counteract the cooling, and so the star stops contracting for a while, forming a dark star some 80 million to 100 million years after the big bang,” said Gondolo. “This is our main result,” he added.
The study also points out that dark stars have some important implications for astrophysics.
For example, their possible existence could aid the search to find and identify dark matter. That is because gamma rays, neutrinos and antimatter have characteristic energy signatures if they come from dark matter.
Also, they could improve understanding of how heavy elements formed. The first stars supposedly were the cradle of elements as heavy or heavier than carbon, producing them via nuclear fusion. But if dark stars existed and did not later evolve into normal stars, they didn’t make carbon. “Maybe carbon came from other stars perhaps conventional stars that formed where there was no dark matter nearby,” said Gondolo.
The existence of dark stars might also explain why black holes formed much faster than expected. The new study says that black holes existed only a few hundred million years after the big bang, yet current theories say they took longer to form. “These dark stars may help. They could collapse into black holes very early because they are very short-lived and formed when the universe was young, at least in one scenario,” said Gondolo.
According to Gondolo, dark stars would contain mostly normal matter, mostly in the form of hydrogen molecules and helium. “But they would be vastly larger and fluffier than the sun and other stars. They would have glowed infrared, which is heat,” he said.
“They are much bigger than the sun, with diameters ranging from about 4 astronomical units (372 million miles, or four times the average distance between the sun and Earth) to 2,000 astronomical units, that is big enough to swallow 15,000 solar systems like our own,” said Gondolo. It is conceivable that gigantic dark stars may exist today, and although they do not emit visible light, they could be detected because they should spew gamma rays, neutrinos and antimatter and be associated with clouds of cold, molecular hydrogen gas that normally wouldn’t harbor such energetic particles. (ANI)

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