New quasar

Print edition : December 28, 2012

Quasar,750 million years after the Big Bang.-

AS far back in time as astronomers have been able to see until now, the universe has had some trace of heavy elements, such as carbon and oxygen. These elements churned from the explosion of massive stars formed the building blocks for planetary bodies and eventually for life on the earth.

Researchers at the Massachusetts Institute of Technology (MIT), the California Institute of Technology, and the University of California at San Diego have peered far back in time, to the era of the first stars and galaxies, and found matter with no discernible trace of heavy elements. To make this measurement, the team analysed light from the most distant known quasar, a galactic nucleus, more than 13 billion light years from the earth.

These quasar observations provide a snapshot of our universe during its infancy, a mere 750 million years after the initial explosion that created it. Analysis of the quasars light spectrum provided no evidence of heavy elements in the surrounding gaseous clouda finding which suggests that the quasar dates to an era nearing that of the universes first stars.

Robert Simcoe of the MIT and his colleagues have published the results from their study in Nature.

An artist's conception of the most distant quasar found to date.-

On the basis of numerous theoretical models, most scientists agree on a general sequence of events during the universes early development: Nearly 14 billion years ago, the Big Bang threw off massive amounts of matter and energy, creating a rapidly expanding universe. In the minutes following the explosion, protons and neutrons collided in nuclear fusion reactions to form hydrogen and helium. Eventually, the universe cooled to a point where fusion stopped generating these basic elements, leaving hydrogen as the dominant constituent. Carbon and oxygen would not form until the first stars appeared.

Astronomers have attempted to identify the point at which the first stars were born by analysing light from more distant bodies. (The farther away an object is in space, the older it is.) Until now, scientists have only been able to observe objects that are less than about 11 billion years old. These objects exhibit heavy elements, suggesting that stars were already plentiful, or at least well established, at that point in the universes history.

The quasar in question, discovered in August 2011, is the most distant of its kind. To study such distant objects, Simcoe and his colleagues built an infrared spectrometer, which they fitted on to the Magellan Telescope, a massive ground-based telescope in Chile. In January 2012, the team trained the telescope on the newly discovered quasar and collected data from its light.

The spectrometer split the incoming light into different wavelengths, which the team plotted on a graph. It then looked for tell-tale dips in the data, correlating various wavelengths with the light absorbed by different chemicals. Each chemical has its own fingerprint. The chemical composition is inferred from the pattern of absorbed light. The group found evidence of hydrogen, but no oxygen, silicon, iron or magnesium in the light data.

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