photo: The "Cores to Disks" Spitzer Legacy team is using the two infrared cameras on NASA's Spitzer Space Telescope to search dense regions of interstellar molecular clouds (known as "cores") for evidence of star formation. Part of the study targeted a group of objects with no known stars to study the properties of such regions before any stars have formed. The first of these "starless cores" to be examined held a surprise: a source of infrared light appeared where none was expected.
The core is known as L1014, the 1,014th object in a list of dark, dusty "clouds" compiled by astronomer Beverly Lynds over 40 years ago. These have proved to be homes to a rich variety of molecules and are the birthplaces of stars and planets.
The Spitzer image is a 3.6 micron (blue), 8.0 micron (green) and 24.0 micron (red) composite image. The light seen in the infrared image originates from very different sources. The bright yellow object at the center of the image is the object detected in the "starless core". The red ring surrounding the object is an artifact of the reduced spatial resolution of the telescope at 24 microns.
At 3.6 microns the light comes mainly from the object at the heart of the core. At longer wavelengths, the light from the object becomes stronger, a signature that it is not a background star. Also in the longer wavelengths (8.0 to 24.0 microns), astronomers saw the glow from interstellar dust, glowing green to red in the Spitzer composite image. This dust consists mainly of a variety of carbon-based organic molecules known collectively as polycyclic aromatic hydrocarbons. The red color traces a cooler dust component.
No previous observations showed any hint of a source in L1014. For example, the visible light image is from the Digital Sky Survey and is a B-, R-, and I-band composite image (wavelengths ranging from 0.4 to 0.7 microns). The dark cloud in the center of the image is the core, completely opaque in the visible due to obscuration by dust.
The L1014 core lies in the direction of Cygnus. It is thought to be about 600 light years away, but the distance is somewhat uncertain.
Release: November 9, 2004
Two new results from NASA's Spitzer Space Telescope released today are helping astronomers better understand how stars form out of thick clouds of gas and dust, and how the molecules in those clouds ultimately become planets.
Two discoveries -- the detection of an oddly dim object inside what was thought to be an empty cloud, and the discovery of icy planetary building blocks in a system believed to resemble our own solar system in its infancy -- were presented today at the first Spitzer science conference in Pasadena, Calif. Since Spitzer science observations began less than one year ago, the infrared capabilities of the space observatory have unveiled hundreds of space objects too dim, cool or distant to be seen with other telescopes.
In one discovery, astronomers have detected a faint, star-like object in the least expected of places -- a "starless core." Named for their apparent lack of stars, starless cores are dense knots of gas and dust that should eventually form individual newborn stars. Using Spitzer's infrared eyes, a team of astronomers led by Dr. Neal Evans of the University of Texas at Austin probed dozens of these dusty cores to gain insight into conditions that are needed for stars to form.
Starless cores are fascinating to study because they tell us what conditions exist in the instants before a star forms. Understanding this environment is key to improving our theories of star formation, said Evans.
But when they looked into one core, called L1014, they found a surprise -- a warm glow coming from a star-like object. The object defies all models of star formation; it is fainter than would be expected for a young star. Astronomers theorize that the mystery object is one of three possibilities: the youngest "failed star," or brown dwarf ever detected; a newborn star caught in a very early stage of development; or something else entirely.
This object might represent a different way of forming stars or brown dwarfs. Objects like this are so dim that previous studies would have missed them. It might be like a stealth version of star formation, Evans said. The new object is located 600 light-years away in the constellation Cygnus.
In another discovery, Spitzer's infrared eyes have peered into the place where planets are born -- the center of a dusty disc surrounding an infant star -- and spied the icy ingredients of planets and comets. This is the first definitive detection of ices in planet-forming discs.
This disc resembles closely how we imagine our own solar system looked when it was only a few hundred thousand years old. It has the right size, and the central star is small and probably stable enough to support a water-rich planetary system for billions of years into the future, said Dr. Klaus Pontoppidan of Leiden Observatory in the Netherlands, who led the team that made this discovery.
Previously, astronomers had seen ices, or ice-coated dust particles, in the large cocoons of gas and dust that envelop young stars. But they were not able to distinguish these ices from those in the inner planet-forming portion of a star's disc. Using Spitzer's ultra-sensitive infrared vision and a clever trick, Pontoppidan and his colleagues were able to overcome this challenge.
photo: (Spitzer Spectrum of Ices in a Protoplanetary Disc)Astronomers have made the first clear detection of a variety of ices -- water, ammonium, and carbon dioxide -- in the inner planet-forming region near a young star about 120 light years away. Such an observation is only possible by combining the unique sensitivity of NASA's Spitzer Space Telescope with the fortunate alignment of this particular system.
Planet-forming discs are seen in a variety of orientations, ranging from edge-on (where the discs block the light of the star entirely) to face-on (where the disc is lost in the glare of the star). In this system, known to astronomers as CRBR 2422.8-3423, the disc lies at a unique angle. The light from the star just peeks out over the disc, like a distant sunrise, and contains clues about the disc material through which it has passed.
These observations use Spitzer's infrared spectrograph which acts much like a prism, spreading light out into its component parts, or spectrum. Astronomers study this infrared rainbow, measuring how much light from the star reaches us at different wavelengths. From this they can determine the composition of the disc.
Different ices in the disc each have their own unique infrared "colors" and will block the light in different parts of the star's spectrum. For example, the dip in the spectrum around 6 microns indicates the presence of water ice. The feature at 7 microns is caused by warmed ammonium ions and therefore must be close to the star, within the inner planet-forming region of the disc.
This result has given astronomers a new tool in probing the inner workings of planet-forming discs. By looking for other young stars with discs lined up at just the right angle, they can learn more about the stuff that formed our own solar system almost 5 billion years ago.
Their trick was to view a young star and its dusty disc at "dawn." Discs can be viewed from a variety of angles, ranging from the side or edge-on, where the discs appear as dark bars, to face-on, where the discs become washed out by the light of the central star. They found that if they observed a disc at a 20-degree angle, at a position where the star peeks out like our Sun at dawn, they could see the ices.
"We hit the sweet spot," said Pontoppidan. "Our models predicted that the search for ices in discs is a problem of finding an object with just the right viewing angle, and Spitzer confirmed that model."
In this system, astronomers found ammonium ions as well as components of water and carbon dioxide ice.
The Spitzer science conference, "The Spitzer Space Telescope: New Views of the Cosmos," is being held at the Sheraton Pasadena hotel.
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