Monday, October 1, 2012

Lonesome Stars Glow In The Background

An ethereal Cosmic Infrared Background Radiation (CIB) travels to Earth from all directions in Space, carrying with it marvelous clues about our Universe's "first fireworks". This lumpy, weak infrared glow, emitted by some mysterious and very ancient objects, first began an incredibly long journey to us in visible or even ultraviolet wavelengths. But, due to the expansion of the Universe, this ancient traveling light was stretched out to longer wavelengths that astronomers now observe as a faint infrared glow all over the entire sky.

The CIB was first discovered in 2005, and then studied more intensely about two years later, by astronomers using NASA's highly successful Spitzer Space Telescope that sees the sky with infrared vision. Spitzer is a remarkable piece of technology that has succeeded in obtaining precious scientific information about the Universe since its launch on August 25, 2003, from Cape Canaveral Air Force Base aboard a Delta II rocket. Spitzer ultimately drifted into a one-of-a-kind Earth-trailing orbit around the Sun, where it now observes an optically invisible Universe heavily cloaked by dust and stars. Glittering starlight is absorbed by dense veiling dust, that is re-emitted in the infrared, and therefore can be observed with Spitzer's infrared eyes. Spitzer is the fourth and final of NASA's Great Observatories program which includes the Hubble Space Telescope (HST), the Compton Gamma-Ray Observatory (CGRO), and the Chandra X-ray Observatory (CXO).

Spitzer has been able to look far back in time to see the lumpy, faint glow of the CIB, emitted by the very first objects dwelling in the ancient Universe. Whereas visible light reveals to astronomers the well-kept secrets of the beautiful incandescent stars that dwell within our Universe's billions and billions of galaxies, the far-infrared is emitted by cold dust that is hiding the newly formed stars like an impenetrable veil. Spotting this surprisingly great multitude of dusty galaxies has proven to be a difficult quest for astronomers. Space telescopes are necessary in order to observe far-infrared light sent forth from the very brightest of the objects that contribute to the infrared background.

In June 2012, astronomers using Spitzer reported that they may have detected these very first objects--our Universe's "first fireworks". The ancient objects may be huge stars--much larger than the familiar stars of today's Cosmos--or hungry black holes. The astronomers were quick to point out that the objects are so remote that they were extraordinarily difficult to resolve individually. However, Spitzer successfully obtained hints of what appears to be an overall pattern formed by their collective light. The observations helped to confirm the idea that these first objects were great in number, and that they burned with furious, brilliant fire.

Dr. Alexander (Sasha) Kashlinsky of NASA's Goddard Space Flight Center in Greenbelt, Maryland, lead author of a research paper discussing the findings that were published in the Astrophysical Journal, told the press on June 7, 2012 that "These objects would have been tremendously bright. We can't yet directly rule out mysterious sources for this light that could be coming from our nearby Universe, but it is now becoming increasingly likely that we are catching a glimpse of an ancient epoch. Spitzer is laying down a roadmap for NASA's upcoming James Webb Telescope, which will tell us exactly what and where these first objects were." The James Webb Space Telescope (JWST) is a large infrared-optimized space telescope currently set for a 2018 launch.

The June 2012 study was designed to improve on earlier observations by measuring the CIB out to scales approximately equal to two full Moons. This is considerably larger than what had been observed previously.

However, in October 2012, other astronomers proposed a different origin for the mysterious softly glowing CIB. This later study also used data from Spitzer, and suggests that the source of the bewitching glow comes from lonesome stars hovering beyond the edges of galaxies. These isolated stars are believed to have once been denizens of these galaxies before violent galaxy mergers tore them away and then hurled them ruthlessly into the empty, cold, dark space outside of their erstwhile homes.

Dr. Asantha Cooray of the University of California at Irvine, lead author of the research published in the journal Nature, explained in an October 24, 2012, Jet Propulsion Laboratory (JPL) Press Release that "The infrared background glow in our sky has been a huge mystery. We have new evidence this light is from the stars that linger between galaxies. Individually, the stars are too faint to be seen, but we think we are seeing their collective glow."

This later study is at variance with the earlier theory proposed by Kashlinsky and his colleagues, who argue that this mysterious glow is emanating from the very first stars and galaxies in the Universe.

In the later study, Cooray and co-workers looked at information gathered from a larger region of the sky, that covered an arc approximately equal to 50 full Moons. These observations, however, were not as sensitive as those from the Kashlinsky group, but the larger scale enabled the Cooray team to better scrutinize the pattern of the CIB light. They surveyed the larger region of the sky, called the Bootes field, for 250 hours.

The Cooray team ultimately reached the conclusion that the pattern of light, seen in the infrared glow, was inconsistent with those theories and computer simulations that suggested it came traveling to Earth from light emitted by the very first stars and galaxies in the Universe. They determined that the glow was too bright to be dispatched from the first galaxies, which were probably not as large or as numerous as the galaxies dwelling in today's Cosmos. Therefore, Cooray's team went on to explain the lumpy all-pervasive infrared glow based on existing theories of "intrahalo" or "intracluster" starlight.

These theories predict that there is a diffuse population of lonely stars dwelling beyond the outer limits of galaxies, as well as in the dark and relatively empty spaces between galaxies. Young galaxies were still growing in size during the Universe's early days, and as they grew, they tended to collide with one another, gaining increasingly more and more mass. As the growing galaxies crashed into one another, they became inextricably intertwined gravitationally, causing lovely ribbons of dazzling stars to be violently shredded, hurling the stars into space. In addition, galaxies also grow when they devour smaller dwarf galaxies, and this can be a very messy dinner. The mess can result in stray stars being thrown out of their galactic homes.

Cooray commented in the October 24, 2012 JPL Press Release that "A light bulb went off when reading some research papers predicting the existence of diffuse stars. They could explain what we are seeing with Spitzer."

More research is needed to determine the true origins of the CIB. Perhaps the keen vision of JWST will at long last solve the lingering mystery once and for all. Dr. Eric Smith, JWST's deputy program manager at NASA Headquarters in Washington, D.C. noted in the October 24, 2012 JPL Press Release that "The keen infrared vision of the James Webb Telescope will be able to see some of the earliest stars and galaxies directly, as well as the stray stars lurking between the outskirts of nearby galaxies. The mystery objects making up the background infrared light may finally be exposed."

I am a writer and astronomer whose articles have been published since 1981 in various journals, magazines, and newspapers. Although I have written on a variety of topics, I particularly love writing about astronomy because it gives me the opportunity to communicate to others the many wonders of my field. My first book, "Wisps, Ashes, and Smoke," will be published soon

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