(Spitzer) Telescope finds planet building blocks around brown space dwarfs

PASADENA, Calif. - A NASA telescope has detected for the first time the building blocks of planets around brown dwarfs, suggesting that such failed stars probably undergo the same planet-building process.

Until now, the microscopic crystal building blocks that eventually collide to form planets have only been seen around stars and comets - considered the remnants of the solar system.

NASA's Spitzer Space Telescope recently spotted the tiny crystals and dust grains circling five brown dwarfs located 520 light years away in the Chamaeleon constellation. The crystals, composed of a green mineral commonly found on Earth known as olivine, are thought to be the building blocks of planets.

Brown dwarfs, like stars, form from thick clouds of gas and dust. But they collapse under their own weight and are considered the older and dimmer cousins to stars.

"We are learning that the first stages of planet formation are more robust than previously believed," said Daniel Apai, an astronomer at the University of Arizona, Tucson.

Astronomers believe planets were born out of disks of dust that surround young stars and brown dwarfs. The particles that make up the disk eventually crystallize and clump together to form planets.

NASA's Spitzer Finds Failed Stars May Succeed in Planet Business

http://www.spitzer.caltech.edu/Media/releases/ssc2005-21/release.shtml

For Release: October 20, 2005

NASA's Spitzer Space Telescope has spotted the very beginnings of what might become planets around the puniest of celestial orbs -- brown dwarfs, or "failed stars."

The telescope's infrared eyes have for the first time detected clumps of microscopic dust grains and tiny crystals orbiting five brown dwarfs. These clumps and crystals are thought to collide and further lump together to eventually make planets. Similar materials are seen in planet-forming regions around stars and in comets, the remnants of our own solar system's construction.

The findings provide evidence that brown dwarfs, despite being colder and dimmer than stars, undergo the same initial steps of the planet-building process.

"We are learning that the first stages of planet formation are more robust than previously believed," said Dr. Dániel Apai, an astronomer at the University of Arizona, Tucson, and member of the NASA Astrobiology Institute's Life and Planets Astrobiology Center. "Spitzer has given us the possibility to study how planets are built in widely different environments."

The observations also imply that brown dwarfs might be good targets for future planet-hunting missions. Astronomers do not know if life could exist on planets around brown dwarfs.

Brown dwarfs differ from stars largely due to their mass. They lack the mass to ignite internally and shine brightly. However, they are believed to arise like stars, out of thick clouds of gas and dust that collapse under their own weight. And like stars, brown dwarfs develop disks of gas and dust that circle around them. Spitzer has observed many of these disks, which glow at infrared wavelengths.

Apai and his team used Spitzer to collect detailed information on the minerals that make up the dust disks of six young brown dwarfs located 520 light-years away, in the Chamaeleon constellation. The six objects range in mass from about 40 to 70 times that of Jupiter, and they are roughly 1 to 3 million years old.

The astronomers discovered that five of the six disks contain dust particles that have crystallized and are sticking together in what may be the early phases of planet assembling. They found relatively large grains and many small crystals of a mineral called olivine.

"We are seeing processed particles that are linking up and growing in size," said Dr. Ilaria Pascucci, a co-author also of the University of Arizona. "This is exciting because we weren't sure if the disks of such cool objects would behave the same way that stellar disks do."

The team also noticed a flattening of the brown dwarfs' disks, which is another sign that dust is gathering up into planets.

A paper on these findings appears online today in Science. Authors of the paper also include Drs. Jeroen Bouwman, Thomas Henning and Cornelis P. Dullemond of the Max Planck Institute for Astronomy, Germany; and Dr. Antonella Natta of the Osservatorio Astrofisico di Arcetri, Italy.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA's Science Mission Directorate. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spitzer's infrared spectrograph, which made the observations, was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck of Cornell. The NASA Astrobiology Institute, founded in 1997, is a partnership between NASA, 16 major U.S. teams and six international consortia.

For more information about the NASA Astrobiology Institute, visit http://nai.arc.nasa.gov/. For more information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/.

PRESS RELEASE
Date Released: Tuesday, April 8, 2003
Source: Royal Astronomical Society

Stellar Census Detects More Red and Brown Dwarfs

Astronomers are honing the skills they need to take a census of the most elusive stars in the Galaxy. A team from Keele University and Exeter University applied a relatively simple test to pick out objects they thought might be faint red dwarfs and their even dimmer cousins, brown dwarfs, belonging to a young star cluster in Orion.

Then, after much more detailed scrutiny, they found they had achieved a 90% hit rate. Their bounty consisted of 67 very low mass objects in the cluster, about half of which are brown dwarfs. Studies like this are very important for refining theories on how stars form and estimating how much of the material in a galaxy is in stars that are impossible to see individually very far beyond our own stellar neighbourhood. Mike Kenyon, a doctoral student from Keele, will present the team's results to date at the UK/Ireland National Astronomy Meeting in Dublin on 9 April.

Stars are born in clusters and the majority of stars are less massive than the Sun: that much is already understood. But when a cluster forms, what is the breakdown in numbers among stars of different masses? The answer to that critical question will help astronomers understand the stellar population of the Milky Way and other galaxies. However, taking the census of the least significant members of a stellar family is still a difficult task to complete. Low mass stars and brown dwarfs shine so weakly, detecting them at all is a real challenge.

With the aim of tackling this problem, Mike Kenyon, Rob Jeffries, and Joana Oliveira of Keele University and Tim Naylor of the University of Exeter observed a large sample of objects suspected of being low-mass members of an association of young stars surrounding the massive hot star, Sigma Orionis. From these, they chose a selection for further examination on the basis that their luminosities and colours hinted that they were likely cluster members. Using the William Herschel Telescope on the island of La Palma, they took spectra of 75 of these candidates.

From the spectra, the researchers could tell whether each object was indeed a cluster member, or an unrelated object that happens to lie in the direction of Sigma Orionis. The outcome was confirmation that at least 90% are cluster members. "We have discovered 67 low-mass members of Sigma Orionis, approximately half of which are brown dwarfs," said Mike Kenyon. "This validates our belief that surveys of colour and luminosity do a reasonable job of detecting cluster members. It gives us a way of counting low-mass stars without having to take detailed spectra, which is difficult and sometimes impossible for the faintest stars."

However, spectra are valuable because they can reveal intimate details of individual stars. "Three of the low-mass objects we have studied so far show very strong evidence that they are accreting matter from a circumstellar disk," says Mike Kenyon, and several may be binary systems. We have more work to do on this but one brown dwarf is a strong contender for being a binary system."

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