* Astronomy

New observations from NASA's Spitzer Space Telescope strongly suggest that infrared light detected in a prior study originated from clumps of the very first objects of the Universe. The recent data indicate this patchy light is splattered across the entire sky and comes from clusters of bright, monstrous objects more than 13 billion light-years away.

"We are pushing our telescopes to the limit and are tantalisingly close to getting a clear picture of the very first collections of objects. Whatever these objects are, they are intrinsically incredibly bright and very different from anything in existence today" - Dr. Alexander Kashlinsky of NASA's Goddard Space Flight Centre, Greenbelt, Md., lead author on two reports to appear in the Astrophysical Journal Letters.

Astronomers believe the objects are either the first stars -- humongous stars more than 1,000 times the mass of our sun -- or voracious black holes that are consuming gas and spilling out tons of energy. If the objects are stars, then the observed clusters might be the first mini-galaxies containing a mass of less than about one million suns. The Milky Way galaxy holds the equivalent of approximately 100 billion suns and was probably created when mini-galaxies like these merged.
This study is a thorough follow-up to an initial observation presented in Nature in November 2005 by Kashlinksy and his team. The new analysis covered five sky regions and involved hundreds of hours of observation time.
Scientists say that space, time and matter originated 13.7 billion years ago in a tremendous explosion called the Big Bang. Observations of the cosmic microwave background by a co-author of the recent Spitzer studies, Dr. John Mather of Goddard, and his science team strongly support this theory. Mather is a co-winner of the 2006 Nobel Prize for Physics for this work. Another few hundred million years or so would pass before the first stars would form, ending the so-called dark age of the universe.
With Spitzer, Kashlinsky's group studied the cosmic infrared background, a diffuse light from this early epoch when structure first emerged. Some of the light comes from stars or black hole activity so distant that, although it originated as ultraviolet and optical light, its wavelengths have been stretched to infrared wavelengths by the growing space-time that causes the universe's expansion. Other parts of the cosmic infrared background are from distant starlight absorbed by dust and re-emitted as infrared light.

"There's ongoing debate about what the first objects were and how galaxies formed. We are on the right track to figuring this out. We've now reached the hilltop and are looking down on the village below, trying to make sense of what's going on" - Dr. Harvey Moseley of Goddard, a co-author on the papers.

The analysis first involved carefully removing the light from all foreground stars and galaxies in the five regions of the sky, leaving only the most ancient light. The scientists then studied fluctuations in the intensity of infrared brightness, in the relatively diffuse light. The fluctuations revealed a clustering of objects that produced the observed light pattern.

"Imagine trying to see fireworks at night from across a crowded city. If you could turn off the city lights, you might get a glimpse at the fireworks. We have shut down the lights of the universe to see the outlines of its first fireworks" - Dr. Alexander Kashlinsky.

Read more

A team of astronomers has uncovered new evidence about the stars whose formation ended the cosmic "Dark Ages" a few hundred million years after the Big Bang.

In a presentation at the 2006 annual winter meeting of the American Astronomical Society (AAS), California Institute of Technology graduate student George Becker discussed his team's investigation of several faraway quasars and the gas between the quasars and Earth. The paper on which his lecture is based will be published in the Astrophysical Journal in March.

One quasar in the study seems to reveal numerous patches of "neutral" gas, made up of atoms where the nucleus and electrons cling together, floating in space when the universe was only about 10 percent of its present age. This gas is thought to have existed in significant quantities only within a certain time-frame in the early universe. Prior to the Dark Ages, all material would have been too hot for atomic nuclei to combine with their electrons; after, the light from newly-formed stars would have reached the atoms and stripped off the electrons.

"There should have been a period when most of the atoms in the universe were neutral. This would have continued until stars and galaxies began forming" - George Becker.

In other words, the universe went from a very hot, very dense state following the Big Bang where all atomic nuclei and electrons were too energetic to combine, to a less dense and cooler phase-albeit a dark one-where the nuclei and the electrons were cool enough to hold onto each other and form neutral atoms, to today's universe where the great majority of atoms are ionised by energetic particles of light.
Wallace Sargent, who coined the term Dark Ages in 1985 and who is Becker's supervising professor, adds that analysing the quasars to learn about the early universe is akin to looking at a lighthouse in order to study the air between you and it. During the Dark Ages, neutral atoms filling the universe would have acted like a fog, blocking out the light from distant objects. To end the Dark Ages, enough stars and galaxies needed to form to burn this "cosmic fog" away.

"We may have detected the last wisps of the fog" - Wallace Sargent, Bowen Professor of Astronomy at Caltech.

The uniqueness of the new study is the finding that the chemical elements of the cool, un-ionised gas seem to have come from relatively ordinary stars. The researchers think this is so because the elements they detect in the gas- oxygen, carbon, and silicon-are in proportions that suggest the materials came from Type II supernovae.
These particular explosions are caused when massive stars collapse and then rebound to form a gigantic explosion. The stars needed to create these explosions can be more than ten times the mass of the sun, yet they are common over almost the entire history of the universe.
However, astronomers believe that the very first stars in the universe would have been much more massive, up to hundreds of times the mass of the sun, and would have left behind a very different chemical signature.

"If the first stars in the universe were indeed very massive stars, then their chemical signature was overwhelmed by smaller, more typical stars very soon after"- George Becker.

Becker and his colleagues believe they are seeing material from stars that was blown into space by the supernovae explosions and mixed with the pristine gas produced by the Big Bang. Specifically, they are looking at the spectra of the light from quasars as it is absorbed during its journey through the mixed-up gas.
The quasars in this particular study are from the Sloan Digital Sky Survey, an ongoing mapping project that seeks, in part, to determine the distances of 100,000 quasars. The researchers focused on nine of the most distant quasars known, with redshifts greater than 5, meaning that the light we see from these objects would have been emitted when the universe was at most 1.2 billion years old.
Of the nine, three are far enough away that they may have been at the edge of the dark period. Those three have redshifts greater than 6, meaning that the universe was less than 1 billion years old when they emitted the light we observe. By comparison, the present age of the universe is believed to be about 13.7 billion years.

The study in part promises a new tool to investigate the nature of stars in the early universe.

"Now that we've seen these systems, it's reasonable to ask if their composition reflects the output of those first very massive stars, or whether the mix of chemicals is what you would expect from more ordinary stars that ended in Type II supernovae. It turns out that the latter is the case. The chemical composition appears to be very ordinary"- George Becker.

Thus, the study provides a new window into possible transitions in the early universe.

"The relative abundance of these elements gives us in principle a way of finding out what the first stars were. This gives us insight into what kind of stars ended the Dark Ages" - Wallace Sargent.

Source