black hole growth
August 12, 2014

Scientists Develop Model To Explain Ancient Black Hole Formation

redOrbit Staff & Wire Reports - Your Universe Online

Several processes typically limit how quickly black holes can grow, so how did those located at the ends of the universe come to have masses equal to several billion suns? Researchers from the Wiezmann Institute of Science and Yale University have proposed a potential solution in the latest edition of the journal Science.

These enormous black holes, the study authors noted in a statement, consume large quantities of interstellar gas on a constant basis. It is through the light that they emit while swallowing up this gas that we can detect them during their formational period, as they appear to us as they were less than one billion years after the Big Bang.

Typically, black holes form when a massive star runs out of nuclear fuel and explodes. Without this fuel at its core resisting gravity, the star collapses and ejects much of its material outwards in a supernova. The remaining material falls inward, forming a black hole that is approximately 10 solar masses in size. The discovery of these ancient quasars, however, has led scientists to wonder how the process could have happened so quickly.

“Several processes tend to limit how fast a black hole can grow,” the Weizmann Institute explained. “For example, the gas normally does not fall directly into the black hole, but gets sidetracked into a slowly spiraling flow, trickling in drop by drop. When the gas is finally swallowed by the black hole, the light it emits pushes out against the gas. That light counterbalances gravity, and it slows the flow that feeds the black hole.”

In order to solve the mystery behind these ancient black holes, Professor Tal Alexander, Head of the Particle Physics and Astrophysics Department at the Weizmann Institute and Professor Priyamvada Natarajan of Yale University, developed a model starting with the formation of a tiny black hole in the earliest days of the universe.

“At that time, cosmologists believe, gas streams were cold, dense, and contained much larger amounts of material than the thin gas streams we see in today’s cosmos,” the Institute said. “The hungry, newborn black hole moved around, changing direction all the time as it was knocked about by other baby stars in its vicinity.”

“By quickly zigzagging, the black hole continually swept up more and more of the gas into its orbit, pulling the gas directly into it so fast, the gas could not settle into a slow, spiraling motion,” it added. “The bigger the black hole got, the faster it ate; this growth rate, explains Alexander, rises faster than exponentially.”

After a period of approximately 10 million years, the black hole would have expanded to a size of roughly 10,000 solar masses, the study authors said. At that point, the growth rate of the quasar would have slowed down, but by this time the black hole would have been well on its way to an eventual weight of at least one billion solar masses.

“Black holes don't actively suck in matter – they are not like vacuum cleaners,” Alexander told on Sunday. “A star or a gas stream can be on a stable orbit around a black hole, exactly as the Earth revolves around the sun, without falling into it.”

“It is actually quite a challenge to think of efficient ways to drive gas into the black hole at a high enough rate that can lead to rapid growth,” he continued, adding that the “theoretical result” of their research “shows a plausible route to the formation of supermassive black holes very soon after the Big Bang.”

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