Saturday, June 20, 2015

Galactic Crashes Fuel Quasars, Study Finds

[Top Row] This is a selection of photos from a Hubble Space Telescope survey of 11 ultra-bright quasars that existed at the peak of the universe's star-formation era, which was 12 billion years ago. The quasars (powered by supermassive black holes) are so compact and bright they make a diffraction-spike pattern in the telescope's optics — an optical artifact typically only produced by bright nearby stars. Despite their brightness, the quasars are actually dimmed by dusty gas around them. The infrared capability of Hubble's Wide Field Camera 3 was able to probe deeply into the material around the quasars.  [Bottom Row]  When the glare of the quasar is subtracted, researchers see evidence for collisions between galaxies. The collisions and mergers gave birth to the quasars by fueling the supermassive black hole at the core of the galaxies. The new images capture the dust-clearing transitional phase in the merger-driven quasar birth. These observations show that the brightest quasars in the universe live in merging galaxies. Credit: NASA, ESA, and E. Glikman (Middlebury College, Vermont)

When galaxies collide, bright things happen in the universe. Using the Hubble Space Telescope’s infrared vision, astronomers have unveiled some of the previously hidden origins of quasars, the brightest objects in the universe. A new study finds that quasars are born when galaxies crash into each other and fuel supermassive, central black holes. “The Hubble images confirm that the most luminous quasars in the universe result from violent mergers between galaxies, which fuels black hole growth and transforms the host galaxies,” said C. Megan Urry, the Israel Munson Professor of Astronomy and Astrophysics at Yale University, and co-author of the study published online June 18 in The Astrophysical Journal.

“These mergers are also the sites of future black hole mergers, which we hope will one day be visible with gravitational wave telescopes,” Urry said.

Discovered in the 1960s, quasars emit a light as bright as that of one trillion stars. Over the past two decades, researchers have concluded that the energy for quasars comes from supermassive black holes inside the cores of distant galaxies.

But where do the supermassive black holes get their fuel? It had been theorized previously that such energy could come from the merger of two galaxies. The new study confirms it by using Hubble’s sensitivity at near-infrared wavelengths of light to see past the intense glow of the quasar, to the host galaxies themselves.

“The Hubble observations are telling us that the peak of quasar activity in the early universe is driven by galaxies colliding and then merging together,” said Eilat Glikman of Middlebury College in Vermont, lead author of the study and a former Yale postdoctoral researcher. “We are seeing the quasars in their teenage years, when they are growing quickly and all messed up.”

Glikman decided to look for “dust reddened quasars” in several ground-based infrared and radio sky surveys. These quasars are enveloped in dust, dimming their visible light.

Using Hubble’s Wide Field Camera 3, Glikman looked at 11 such quasars from the peak of the universe’s star-formation era, 12 billion years ago. “The new images capture the dust-clearing transitional phase of the merger-driven black hole scenario,” Glikman said. “The Hubble images are both beautiful and descriptive.”

"We've been trying to understand why galaxies start feeding their central black holes, and galaxy collisions are one leading hypothesis. These observations show that the brightest quasars in the universe really do live in merging galaxies," said co-investigator Kevin Schawinski of the Swiss Federal Institute of Technology in Zurich.

Other authors of the study were Brooke Simmons of Oxford University, a former graduate student at Yale; Madeline Mailly of Middlebury College and M. Lacy of the National Radio Astronomy Observatory in Charlottesville, Va.

1 comment:

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