Spitzer picks up glow of Universe's first objects

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

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.

Image Credit: NASA/JPL-Caltech/A. Kashlinsky (GSFC)
High resolution image (1.8 MB)

The right panel is an image from Spitzer Space Telescope of stars and galaxies in the Ursa Major constellation. This infrared image covers a region of space so large that light would take up to 100 million years to travel across it. The left panel is the same image after stars, galaxies and other sources were masked out. The remaining background light is from a period of time when the universe was less than one billion years old, and most likely originated from the universe's very first groups of objects -- either huge stars or voracious black holes. Darker shades in the image on the left correspond to dimmer parts of the background glow, while yellow and white show the brightest light.




Image Credit: NASA/JPL-Caltech/A. Kashlinsky (GSFC)
High resolution image (1.4 MB)

This artist's timeline chronicles the history of the universe, from its explosive beginning to its mature, present-day state.

Our universe began in a tremendous explosion known as the Big Bang about 13.7 billion years ago (left side of strip). Observations by NASA's Cosmic Background Explorer and Wilkinson Anisotropy Microwave Probe revealed microwave light from this very early epoch, about 400,000 years after the Big Bang, providing strong evidence that our universe did blast into existence. Results from the Cosmic Background Explorer were honored with the 2006 Nobel Prize for Physics.

A period of darkness ensued, until about a few hundred million years later, when the first objects flooded the universe with light. This first light is believed to have been captured in data from Spitzer Space Telescope. The light detected by Spitzer would have originated as visible and ultraviolet light, then stretched, or redshifted, to lower-energy infrared wavelengths during its long voyage to reach us across expanding space. The light detected by the Cosmic Background Explorer and the Wilkinson Anisotropy Microwave Probe from our very young universe traveled farther to reach us, and stretched to even lower-energy microwave wavelengths.

Astronomers do not know if the very first objects were either stars or quasars. The first stars, called Population III stars (our star is a Population I star), were much bigger and brighter than any in our nearby universe, with masses about 1,000 times that of our sun. These stars first grouped together into mini-galaxies. By about a few billion years after the Big Bang, the mini-galaxies had merged to form mature galaxies, including spiral galaxies like our own Milky Way. The first quasars ultimately became the centers of powerful galaxies that are more common in the distant universe.

Hubble Space Telescope has captured stunning pictures of earlier galaxies, as far back as ten billion light-years away.

"There's ongoing debate about what the first objects were and how galaxies formed," said Dr. Harvey Moseley of Goddard, a co-author on the papers. "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."

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," said Kashlinsky. "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."

Mather, who is senior project scientist for NASA's future James Webb Space Telescope, said, "Spitzer has paved the way for the James Webb Space Telescope, which should be able to identity the nature of the clusters."

This analysis was partially funded through the National Science Foundation. Science support to NASA Goddard is supplied by Science Systems and Applications, Inc. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. The observations were made by Spitzer's infrared array camera, which was built by NASA's Goddard Space Flight Center, Greenbelt, Md. The instrument's principal investigator is Dr. Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

Jet Propulsion Laboratory News Release