Supermassive black holes spend half their lives veiled in dust

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Washington, March 26 (ANI): A new study by astronomers at Yale University and the University of Hawaii has determined that after undergoing huge growth spurts as a result of galactic collisions, supermassive black holes spend half their lives veiled in dust.

As massive, gas-rich galaxies in the distant universe collide, the central black hole feeds on gas that is funneled to the center of the merger.

"As a result of the violent, messy collision, the black hole also remains obscured behind a 'veil' of dust for between 10 million and 100 million years," said Priyamvada Natarajan, professor of astronomy at Yale and one of the study paper's authors.

After that time, the dust is blown away to reveal a brightly shining quasar-the central region of a galaxy with an extremely energetic, supermassive black hole at its center-that lasts for another 100 million years, the team found.

Until now, astronomers were unsure how long the quasars spent behind the dust cloud.

While unobscured quasars, which are the brightest optical objects in the early universe, were discovered in the late 1950s, examples of quasars obscured by dust were more difficult to detect, and were only discovered in the late 1990s.

"For many years, astronomers believed that these sources were very rare. Now we are seeing them everywhere," said Ezequiel Treister of the University of Hawaii, lead author of the study.

The team used observations from the Hubble, Chandra and Spitzer space telescopes to identify a large number of obscured, dust-enshrouded quasars up to 11 billion light years away, when the universe was only about one-fifth its current age.

"We detected a signature of very hot dust at infrared and X-ray wavelengths to find these obscured sources," Treister said.

"Once they had been identified, we used Hubble's new Wide Field Camera 3-which astronauts installed last year during the final servicing mission-to confirm that these distant quasars were actually the result of mergers," said Kevin Schawinski, another Yale co-author.

The astronomers coupled the telescope observations with estimated galaxy merger rates and theoretical models to come up with the amount of time it takes for the black hole to blow away the surrounding dust and gas and reveal the naked, bright quasar.

"We found that these growing black holes spend about half their lives veiled in dust, and half their lives unveiled," Natarajan said.

"That means that, until now, we have likely been missing half of the actively growing black holes in the early universe," she added. (ANI)

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