Thursday, November 26, 2015         

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UH astrophysicist helps discover infant black holes

By Gregg K. Kakesako


A team of astrophysicists, including one from the University of Hawaii, has found the first evidence of baby black holes created at the dawn of the universe.

"Until now, we had no idea what the black holes in these early galaxies were doing, or if they even existed," said Ezequiel Treister of UH, lead author of the study appearing in today's issue of the journal Nature. "Now we know they are there, and they are growing like gangbusters."

The astrophysicists used NASA's orbiting Chandra X-Ray Observatory and found the first direct evidence that massive black holes were common in the early universe, according to a NASA news release. No one knows how the first black holes were formed after the Big Bang, the initial explosion that created our universe, but they occur when stars implode, creating a gravitation collapse that collects and compresses mass in such a way that no light waves can escape.

Scientists believe that the black holes are growing in connection with the galaxies where they were found and that very young black holes grew more aggressively than previously thought, in tandem with the growth of their host galaxies.

A population of young black holes in the early universe had been predicted, but not yet observed. Detailed calculations show that the total amount of black hole growth observed by this team is about a hundred times higher than recent estimates, NASA said.

<t-7>Because these black holes are nearly all enshrouded in thick clouds of gas and dust, optical telescopes frequently cannot detect them. However, the high energies of X-ray light can penetrate these veils, allowing the black holes inside to be studied.<t$>

Treister said at the news conference, "We found evidence of a very large number of massive black holes when the universe was less than a billion light-years old."

Scientists estimate the universe is 13.7 billion years old.

The supersized growth means that the black holes in the CDFS are less extreme versions of quasars — luminous, rare objects powered by material falling onto supermassive black holes, NASA said. However, the sources in the CDFS are about a hundred times fainter and the black holes are about a thousand times less massive than the ones in quasars. The observations found that between 30 percent and 100 percent of the distant galaxies contain growing, supermassive black holes. Extrapolating these results from the small observed field to the full sky, there are at least 30 million supermassive black holes in the early universe. This is 10,000 times larger than the estimated number of quasars in the early universe.

Treister said the "most exciting" thing about his team's finding was that "we found about 100 times more growth in black hole growth in the universe" than what was known before.

Chandra is capable of detecting extremely faint objects at vast distances, but these black holes are so obscured that relatively few photons can escape and hence they could not be individually detected. Instead, the team used a technique that relied on Chandra's ability to accurately determine the direction from which the X-rays came to add up all the X-ray counts near the positions of distant galaxies and find a statistically significant signal.

Treister said, "This is a big step, not a baby step, in getting closer to understand where the black holes were formed and when they were created and when they started. That was very exciting."

The news conference to discuss the study was held at NASA's Washington, D.C., headquarters, and Treister appeared with other scientists on the project.

Treister is an astrophysicist for the Institute for Astronomy at the University of Hawaii at Manoa. He has a doctorate in astronomy from the Universidad de Chile, two master's degrees in astronomy from Yale University and a bachelors in physics, also from Universidad de Chile.

Chandra was launched in 1999 aboard the space shuttle Columbia. The Chandra X-Ray Observatory is part of NASA's fleet of "Great Observatories" along with the Hubble Space Telescope; the Spitzer Space Telescope, launched in 2003; and the Compton Gamma Ray Observatory, which orbited Earth from 1991-2000.

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