“Lighting Up the Universe” –Black-Hole Creation Triggered By Colliding Galaxies

 

 

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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.

The composite Hubble image below shows what was happening in the universe 12 billion years ago, when the cosmos was smaller and so crowded that galaxies collided with each other much more frequently than today. Hubble astronomers looked at dusty quasars where their glow was suppressed by dust, allowing a view of the quasar's surroundings.

 

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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."

 

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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."

The image at the top of the page shows a galaxy that is not only the farthest one till date, but also exceptionally luminous. According to Yale researchers, the galaxy was formed when the universe was only 5 per cent of its current age.
The galaxy was originally identified based on its particular colors in images from NASA’s Hubble and Spitzer space telescopes. It is one of the brightest and most massive objects in the early universe.

“One of the most dramatic discoveries from Hubble and Spitzer in recent years is the unexpected number of these very bright galaxies at early times close to when the first galaxies formed. We still don’t fully understand what they are and how they relate to the very numerous fainter galaxies,” said coauthor Garth Illingworth, professor of astronomy and astrophysics at UC Santa Cruz.

“It has already built more than 15% of the mass of our own Milky Way today,” said Pascal Oesch, a Yale astronomer. “But it had only 670 million years to do so. The universe was still very young then.” The new distance measurement also enabled the astronomers to determine that EGS-zs8-1 is still forming stars rapidly, about 80 times faster than our galaxy.

The new observations establish EGS-zs8-1 at a time when the universe was undergoing an important change: The hydrogen between galaxies was transitioning from a neutral state to an ionized state. “It appears that the young stars in the early galaxies like EGS-zs8-1 were the main drivers for this transition, called reionization,” said Rychard Bouwens of the Leiden Observatory, co-author of the study.

Taken together, the new Keck Observatory, Hubble, and Spitzer observations also pose new questions. They confirm that massive galaxies already existed early in the history of the universe, but they also show that those galaxies had very different physical properties from what is seen around us today. Astronomers now have strong evidence that the peculiar colors of early galaxies — seen in the Spitzer images — originate from a rapid formation of massive, young stars, which interacted with the primordial gas in these galaxies.

The Daily Galaxy via Yale University

 

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