Thursday, November 6, 2014

CIBER: Caltech rocket experiment finds surprising cosmic light

The entrance of the CIBER optics, showing two near-infrared wide-field cameras (top), an absolute spectrometer (lower left) and a Fraunhofer line spectrometer (lower right). 

Credit: Jamie Bock/Caltech

Using an experiment carried into space on a NASA suborbital rocket, astronomers at Caltech and their colleagues have detected a diffuse cosmic glow that appears to represent more light than that produced by known galaxies in the universe.

The researchers, including Caltech Professor of Physics Jamie Bock and Caltech Senior Postdoctoral Fellow Michael Zemcov, say that the best explanation is that the cosmic light originates from stars that were stripped away from their parent galaxies and flung out into space as those galaxies collided and merged with other galaxies.

This explanation is described in a paper published November 7 in the journal Science,

The discovery suggests that many such previously undetected stars permeate what had been thought to be dark spaces between galaxies, forming an interconnected sea of stars.

"Measuring such large fluctuations surprised us, but we carried out many tests to show the results are reliable," says Zemcov, who led the study.

Although they cannot be seen individually, "the total light produced by these stray stars is about equal to the background light we get from counting up individual galaxies," says Bock, also a senior research scientist at JPL.

Bock is the principal investigator of the rocket project, called the Cosmic Infrared Background Experiment (CIBER), which originated at Caltech and flew on four rocket flights from 2009 through 2013.

In earlier studies, NASA's Spitzer Space Telescope, which sees the universe at longer wavelengths, had observed a splotchy pattern of infrared light called the cosmic infrared background.

The splotches are much bigger than individual galaxies.

"We are measuring structures that are grand on a cosmic scale," says Zemcov, "and these sizes are associated with galaxies bunching together on a large-scale pattern."

Initially some researchers proposed that this light came from the very first galaxies to form and ignite stars after the Big Bang.

Others, however, have argued the light originated from stars stripped from galaxies in more recent times.

CIBER was designed to help settle the debate. "CIBER was born as a conversation with Asantha Cooray, a theoretical cosmologist at UC Irvine and at the time a postdoc at Caltech with [former professor] Marc Kamionkowski," Bock explains.

"Asantha developed an idea for studying galaxies by measuring their large-scale structure. Galaxies form in dark-matter halos, which are over-dense regions initially seeded in the early universe by inflation.

Furthermore, galaxies not only start out in these halos, they tend to cluster together as well. Asantha had the brilliant idea to measure this large-scale structure directly from maps.

Experimentally, it is much easier for us to make a map by taking a wide-field picture with a small camera, than going through and measuring faint galaxies one by one with a large telescope."

More information: On the Origin of Near-Infrared Extragalactic Background Light Anisotropy, Science,… 1126/science.1258168

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