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TOPIC: Brown Dwarfs


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Date:
WD0137-349
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A distant world that escaped the likely fate of the Earth - being fried when the Sun grows old and dies - has been discovered by UK astronomers.

The brown dwarf withstood being swallowed by a red giant and is now locked in a perpetual dance with the remains of the larger star.
The two objects, of different colours, rotate around each other in two hours.
The findings, reported in Nature, suggest some planets might also survive the natural death throes of stars.
The fate of most stars is to grow old, run out of hydrogen fuel, then collapse under its own gravity.
The atmosphere becomes unstable and starts to expand, transforming the star into what is known as a red giant.
The dying core eventually turns into a white dwarf - a spherical body the size of the Earth, made up of carbon and oxygen.
The star then gradually fades away, becoming dimmer and dimmer until its light is finally extinguished.
If a star fails early its history, before it is fully born, it is known as a brown dwarf; a cold, dim body intermediate in size between a very large planet and a Sun-like star.
Until now, astronomers believed something as small, in relative terms, as a brown dwarf could not emerge unscathed from immersion in the fiery furnace of a dying star.

"We've discovered a small failed star called a brown dwarf lying next to another star called a white dwarf and the two are orbiting each other in a tiny orbit of two hours. We've found something 55 times more massive than Jupiter that has survived being swallowed by a red giant; can something smaller, like a known extrasolar planet, also survive?" - Dr Matt Burleigh, a co-author of the paper and an astronomer at the University of Leicester.

Dr Burleigh believes it is unlikely that something as small and rocky as Earth could escape the fate of incineration some four billion years from now.
But he believes one of the 200 or so extra-solar planets - a planet which orbits a star other than the Sun, and therefore belongs to a planetary system other than the Solar System - might just make it.

"My guess is that the Earth probably couldn't survive because it is so much less massive than a brown dwarf. But whether other big planets, Jupiter-size or bigger, could is an interesting question" - Dr Matt Burleigh.

The Leicester team, and colleagues at the Universities of Hertfordshire and Keele, think the brown dwarf survived being engulfed by the red giant because the envelope of the giant was ejected very rapidly.

"Prior to this discovery, you would expect the brown dwarf to be swallowed and crash into the core of the red giant but it seems it was able to eject the atmosphere of the red giant before it crashed into the core" - Dr Matt Burleigh.

The two objects have ended up separated by less than two-thirds of the radius of the Sun or only a few thousandths of the distance between the Earth and the Sun.
They rotate around each other in about two hours, the brown dwarf moving on its orbit at a speed of 800,000km/h.
Despite this temporary reprieve from destruction, it is not all good news for the brown dwarf. Einstein's General Theory of Relativity predicts that the gap between the two stars will slowly decrease.

"Thus, in about 1.4bn years, the orbital period will have decreased to slightly more than one hour. At that stage, the two objects will be so close that the white dwarf will work as a giant 'vacuum cleaner', drawing gas off its companion, in a cosmic cannibal act" - Ralf Napiwotzki, from the University of Hertfordshire.

WD0137349

The companion to the white dwarf goes under the official name of WD0137-349. It was found using the European Southern Observatory's (ESO's) New Technology Telescope at La Silla in Chile.

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-- Edited by Blobrana at 18:41, 2006-08-02

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RE: Brown Dwarfs
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Astronomers have discovered that the large disks of gas and dust around young stars will fragment if two young stars pass close to each other and form smaller brown dwarfs stars with disks of their own. The news was announced this week at the Canadian Astronomical Society in Calgary, Alta, by James Wadsley, assistant professor of Physics & Astronomy at McMaster University, and his student Sijing Shen.

"This is an exciting discovery because it may be the dominant way brown dwarfs are made. The challenge to theorists was to explain not only the origin of brown dwarfs but also the details telescopes are seeing: brown dwarfs with disks and the systems of many dwarfs orbiting a single regular star. We've done that" - James Wadsley.

Brown dwarf stars are as common in number as large stars but are no more than 8 percent of the mass of the Sun. Their low mass prevents nuclear fusion in their core so they don't shine like regular stars. Regular stars form from cold dense cores in giant molecular gas clouds. The natural mass of a core is expected to be large, closer to that of a regular star than a brown dwarf so something extra was required to understand the origin of brown dwarfs.

Using SHARCNET (Shared Hierarchical Academic Research Computing Network) parallel computing facilities at McMaster, Shen and Wadsley simulated several encounters between young stars with disks at unprecedented resolution, seeing gas pile-ups, drawn-out tidal arms and huge masses of gas driven closer to the stars. Amid this chaos several small objects were seen to form, from Jupiter-sized objects up to brown dwarfs. Reports from lower resolution simulations by other groups had shown no indication of disks. However, in every case, the new objects had disks with sizes ranging up to 18 astronomical units (the size of Saturn's orbit). As these rapidly spinning disks evolve they should produce jets of gas and even result in the formation of planets orbiting the brown dwarfs. Both these things have been observed in nature.

"We had no idea the simulated results would be so beautiful and complex, and then we found out that observations were revealing brown dwarfs with disks that matched what we were seeing " - Sijing Shen, who is studying for her PhD in Physics & Astronomy at McMaster.

The simulated objects would either leave the stars on their own or in groups, or remain as multiple brown dwarf companions to a star. Telescopes have detected up to three brown dwarfs orbiting a regular star. Thus the brown dwarfs and planets in the simulations are remarkably similar to what is observed. However, it remains to be determined exactly how often such encounters occur in nature and what fraction of those encounters reliably produce brown dwarfs. For this, Shen and Wadsley are planning a much larger set of encounter simulations using SHARCNET's new supercomputers.

Source: McMaster University

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Date:
SCR 1845-6357
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The Sun's New Exotic Neighbour: A Very Cool Brown Dwarf

Using the European Southern Observatory's Very Large Telescope in Chile, an international team of researchers discovered a brown dwarf belonging to the 24th closest stellar system to the Sun. Brown dwarfs are intermediate objects that are neither stars nor planets. This object is the third closest brown dwarf to the Earth yet discovered, and one of the coolest, having a temperature of about 750 degrees Centigrade. It orbits a very small star at about 4.5 times the mean distance between the Earth and the Sun. Its mass is estimated to be somewhere between 9 and 65 times the mass of Jupiter.

At a time when astronomers are peering into the most distant Universe, looking at objects as far as 13 billion light-years away, one may think that our close neighbourhood would be very well known. Not so. Astronomers still find new star-like objects in our immediate vicinity. Using ESO's VLT, they just discovered a brown dwarf companion to the red star SCR 1845-6357, the 36th closest star to the Sun.


Position(2000): RA = 18h 45m 02.6s Dec = −45° 01′06″
Three-colour image of SCR1845-6357AB generated from the SDI filter images (blue=1.575 micron, green=1.600 micron, red=1.625 micron). Since the T-dwarf fades away towards the longer wavelengths, it appears quite blue in this image. It is roughly 50 times fainter than the star and is separated from it by an angle of 1.17 arcsecond on the sky (4.5 times the Earth-Sun distance).

"This newly found brown dwarf is a valuable object because its distance is well known, allowing us to determine with precision its intrinsic brightness. Moreover, from its orbital motion, we should be able in a few years to estimate its mass. These properties are vital for understanding the nature of brown dwarfs" - team member Markus Kasper (ESO).

To discover this brown dwarf, the team used the high-contrast adaptive optics NACO Simultaneous Differential Imager (SDI) on ESO's Very Large Telescope, an instrument specifically developed to search for extrasolar planets. The SDI camera enhances the ability of the VLT and its adaptive optics system to detect faint companions that would normally be lost in the glare of the primary star. In particular, the SDI camera provides additional, often very useful spectral information which can be used to determine a rough temperature for the object without follow-up observations.

Located 12.7 light-years away from us, the newly found object is nevertheless not the closest brown dwarf. This honour goes indeed to the two brown dwarfs surrounding the star Epsilon Indi, located 11.8 light years away.

However, this newly discovered brown dwarf is unique in many aspects.

"Besides being extremely close to Earth, this object is a T dwarf - a very cool brown dwarf - and the only such object found as a companion to a low-mass star. It is also likely the brightest known object of its temperature because it is so close" - Beth Biller, a graduate student at the University of Arizona and lead author of the paper reporting the discovery.

The discovery of this brown dwarf hints that, at least close to the Sun, cool brown dwarfs prefer to be part of a couple with a star or another brown dwarf, rather than wandering alone in the cosmic emptiness. Indeed, of the seven cool brown dwarfs that reside within 20 light years of the Sun, five have a companion.

"This has wide-ranging implications for theories of brown dwarf formation, which, until now, tend to favour the production of single brown dwarfs" - team member Laird Close (University of Arizona).

The work presented here will appear as a Letter to the Editor in the Astrophysical Journal ("Discovery of a Very Nearby Brown Dwarf to the Sun: A Methane Rich Brown Dwarf Companion to the Low Mass Star SCR 1845-6357", by B. Biller et al.).

Source




Title: Discovery of a Very Nearby Brown Dwarf to the Sun: A Methane Rich Brown Dwarf Companion to the Low Mass Star SCR 1845-6357
Authors: B.A. Biller, M. Kasper, L.M. Close, W. Brandner, S. Kellner

We present VLT/NACO SDI images of the very nearby star SCR 1845-6357 (hereafter SCR 1845). SCR 1845 is a recently discovered (Hambly et al. 2004) M8.5 star just 3.85 pc from the sun (Henry et al. 2006). Using the capabilities of the unique SDI device, we discovered a substellar companion to SCR 1845 at a separation of 4.5 AU (1.170''±0.003'' on the sky) and fainter by 3.57±0.057 mag in the 1.575 um SDI filter. This substellar companion has an H magnitude of 13.16+0.31-0.26 (absolute H magnitude of 15.30+0.31-0.26), making it likely the brightest mid-T dwarf known. The unique Simultaneous Differential Imager (SDI) consists of 3 narrowband filters placed around the 1.6 um methane absorption feature characteristic of T-dwarfs (Teff < 1200 K). The flux of the substellar companion drops by a factor of 2.7+-0.1 between the SDI F1(1.575 um) filter and the SDI F3(1.625 um) filter, consistent with strong methane absorption in a substellar companion. We estimate a spectral type of T5.5±1 for the companion based on the strength of this methane break.
The chances that this object is a background T dwarf are vanishing small -- and there is no isolated background T-dwarf in this part of the sky according to 2MASS. Thus, it is a bound companion, hereafter SCR 1845-6357B. For an age range of 100 Myr - 10 Gyr and spectral type range of T4.5-T6.5, we find a mass range of 9 - 65 MJup for SCR 1845B from the Baraffe et al. 2003 COND models. SCR 1845AB is the 24th closest stellar system to the Sun (at 3.85 pc); the only brown dwarf system closer to the Sun is Eps Indi Ba-Bb (at 3.626 pc). In addition, this is the first T-dwarf companion discovered around a low mass star.

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Posts: 131433
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2MASS J05352184–0546085
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The eclipsing binary brown dwarfs 1,400 light-years away in the Orion nebula, have masses of 55 times Jupiter's mass, and 35 times Jupiter's mass (with a 10 percent margin of error).



The astronomers also measured the light spectrum variations and determined the dwarfs' surface temperatures. The heavier of the two has a temperature of 2,650 degrees Kelvin and the smaller, 2,790 degrees K.


Position (2000): R.A. = 05 h 35 m 21 s.84 Dec. = -05° 46 ' 08 ".5

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The discovery of the paired brown dwarfs 1,400 light-years away in the Orion nebula, and the critical measurements are reported today in the scientific journal Nature by a team of astronomers: Jeff Valenti of the Space Telescope Science Institute (STScI), Robert Mathieu of the University of Wisconsin-Madison, and Keivan Stassun of Vanderbilt University.

One dwarf is 55 times Jupiter's mass; the other is 35 times heftier than Jupiter (with a 10 percent margin of error). To qualify as a star and burn hydrogen through nuclear fusion, the dwarfs would have to be 80 times more massive than Jupiter.

The brown dwarf pair orbits each other so closely that they look like a single object (2MASS J05352184–0546085) when viewed from Earth. Because their racetrack orbit is edge-on, the two objects periodically pass in front of, or eclipse, each other. These eclipses cause regular dips in the brightness of the combined light coming from both objects. By precisely timing these occultations the astronomers were able to determine the orbits of the two objects. With this information, the astronomers used Newton's laws of motion to calculate the mass of the two dwarfs.

In addition, the astronomers calculated the size of the two dwarfs by measuring the duration of the dips in their light curve. Because they are so young, the dwarfs are remarkably large for their mass.
An analysis of the light coming from the dwarf pair indicates that the dwarfs have a reddish cast. Current models also predict that brown dwarfs should have "weather" — cloud-like bands and spots similar to those visible on Jupiter and Saturn.

By measuring variations in the light spectrum coming from the pair, the astronomers also determined the dwarfs' surface temperatures. Theory predicts that the more massive member of a pair of brown dwarfs should have a higher surface temperature. But they found just the opposite. The heavier of the two has a temperature of 2,650 degrees Kelvin and the smaller, 2,790 degrees K.

Position (2000): R.A. = 05 h 35 m 21 s.84 Dec. = -05° 46 ' 08 ".5

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Astronomers have made the first direct measurements of the mass of a pair of brown dwarfs in the Orion Nebula. They used precise timings of the orbital period during which one eclipsed the other, dimming their collective brightness to weigh the failed stars.

Brown dwarfs have a masses between 13 to 75 times the mass of Jupiter.
Scientists believe brown dwarfs form through the collapse of clouds of interstellar gas and dust, like stars. But they lack the mass needed to initiate the nuclear reactions that convert hydrogen to helium in stars.


The I-band light curve of 2MASS J05352184–0546085. In total, 1590 individual flux measurements were obtained on 280 separate nights over 10 years, with an average cadence of 5-6 measurements per night. The typical uncertainty on the measurements is 2%. A time-series analysis reveals a period of P = 9.779621 ± 0.000042 days. The data here are phased relative to the time of periastron passage, as determined from the orbit solution

"If we want to understand how stars like the Sun come to be, we need to also understand when and under what circumstances they fail to be born" - Keivan Stassun at Vanderbilt University in Nashville, Tennessee, US.

Keivan Stassun and Robert Mathieu of University of Wisconsin-Madison and Jeff Valenti of the Space Telescope Science Institute in Baltimore, Maryland, both in the US using the 0.9-metre telescope at Kitt Peak National Observatory and a trio of telescopes at the Cerro Tololo Inter-American Observatory in the Chilean Andes, found that the eclipsing binary brown dwarfs to be about 5% and 3.5% the mass of the Sun, respectively. It is the first time scientists have directly measured a brown dwarf's mass.

The researchers made more than 1500 measurements of the brown dwarfs located in the stellar nursery of the Orion Nebula, over 280 nights between 1994 and 2005.

"The reason that is ultimately important is that these two brown dwarfs now serve as a kind of Rosetta Stone" - Keivan Stassun.

Since the researchers measured the diameter, brightness, surface temperature and mass of each dwarf in the pair, they hope to use the results to evaluate suspected brown dwarfs for which a mass cannot be directly determined.
The observations agree with brown dwarf theory. The newly found brown dwarfs have nearly the same diameter as the Sun and are thought to be only a few million years old.
They are expected to collapse down over a couple hundred million years to become more planet-sized.

But the authors admit that theory and observation did not line up perfectly. Although theory predicts more massive brown dwarfs will be hotter. Surprisingly, the more massive brown dwarf in this system is found to be cooler than its lower-mass companion. This may indicate a younger age for the more massive brown dwarf, which would suggest that these brown dwarfs were not born together

The team suggests several possible explanations for the unexpected result. It could be that the more massive brown dwarf is a bit older, and therefore farther along in the shrinking and cooling process. In that case, the two brown dwarfs would not have been born together.

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Date:
L1521F
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Expand (698kb, 2475 x 1854)
L1521F is a dense “core” in Taurus that may contain a brown dwarf.
CreditPhilip Myers, Harvard-Smithsonian CfA/NASA/JPL-Caltech (SSC)


Expand (327kb, 2100 x 1500)
Blue dots are Spitzer observations in mid-infrared of the lowest-mass brown dwarfs studied (~ 10 Jupiter masses). The black curve is the predicted model of the brown dwarf emission. The green curve is the model of emission of a disk-surrounded brown dwarf — which the data fit.
Credit Katelyn Allers, UT-Austin/NASA/JPL-Caltech (SSC)

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Very Low Luminosity Objects
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A group of astronomers led by Neal Evans of The University of Texas at Austin has used NASA’s Spitzer Space Telescope to show that brown dwarfs form like stars — by pulling in matter from a collapsing gas cloud and forming disks of potentially planet-forming material around themselves — and that such disks are common around young brown dwarfs.
The formation process that creates brown dwarfs has long been a mystery.

"Brown dwarfs are found in the ‘no-man’s land’ between stars and planets. They have masses too small to be a star, but too large to be a planet" - Neal Evans.

Two lines of evidence point to a star-like formation process for brown dwarfs: the presence of disks found around brown dwarfs, and the discovery of extremely dim objects forming inside clouds of gas and dust — objects too dim to be protostars.
Both lines of evidence come from Spitzer observations by Evans’ team, a group of about 60 astronomers from various institutions, called the “Cores to Disks” or “c2d” Spitzer Legacy Project.

"None of these objects could have been found without the unprecedented sensitivity of the instruments on the Spitzer Space Telescope" - Neal Evans.

First, the new c2d Spitzer observations, combined with supporting observations from a number of ground-based telescopes, show that a substantial number of brown dwarfs are surrounded by disks of dusty material, similar to those found around forming stars.
C2d team members Katelyn Allers, Jacqueline Kessler-Silacci, Daniel Jaffe, and Lucas Cieza of The University of Texas at Austin found about a dozen disk-surrounded brown dwarfs in the southern-hemisphere constellations Chamaeleon, Lupus, and Ophiuchus. Some of the brown dwarfs have a mass of five to 10 Jupiters, and are only a few million years old — young, astronomically speaking.

The disk discoveries were made by comparing observations of these objects at different wavelengths. The brown dwarfs were first studied in near-infrared light using the four-meter Blanco Telescope at the National Science Foundation’s Cerro Tololo Interamerican Observatory in Chile.
Astronomers used the near-infrared information to predict how much mid-infrared light they should give off. The Spitzer observations showed that the objects gave off much more mid-infrared light than expected. This can be explained by the presence of a disk around the brown dwarf. Disks are made up of dust, which absorbs light radiated from the brown dwarf and re-emits it at lower energies — that is, in the particular mid-infrared wavelengths detectable by Spitzer.

The group also found these objects are less massive than the smallest stars.

"You can’t weigh these brown dwarfs directly. We used theoretical models to figure out that they may have masses as low as five to 10 Jupiter masses. The disks around the brown dwarfs are analogous to the disks around very young Sun-like stars; disks that we believe provide the raw materials for planets" - Katelyn Allers.

Daniel Apai of the University of Arizona and his collaborators announced in October 2005 that they had found evidence that disks around more massive brown dwarfs might form planets.
Allers’ discoveries broaden the original finding of a disk around the more massive brown dwarf OTS 44 by Kevin Luhman of Penn State, announced in February 2005, and his more recent discovery of a less massive disk-surrounded brown dwarf. The c2d announcement shows these are part of a wide-spread phenomenon — not oddballs, but the norm.

The presence of these disks around brown dwarfs challenges one idea for their formation, namely ejection caused by gravitational interactions inside a region of star formation densely packed with stars. These results conflict with that theory in three ways: First, computer models show that it would be difficult for ejected brown dwarfs to keep their disks. Second, one of Allers’ brown dwarfs is in a wide binary system, which is difficult for the ejection model to produce. Finally, neither Lupus nor Chamaeleon are forming stars in the dense clusters the ejection model requires.

The discovery of a substantial number of disks around even very low mass brown dwarfs increases the likelihood that the alternative formation scenario applies: that brown dwarfs form more or less like stars do, by accreting matter from a collapsing cloud of gas and dust — or, in the jargon of star-formation researchers, a “core.”

"These results suggest an origin for brown dwarfs similar to that of stars: a collapsing ‘core’ of gas and dust. If this is right, we should see evidence for very low mass objects in cores" - Neal Evans

Mass is hard to measure in the very early stages of brown-dwarf formation. But astronomers know that forming objects give off light in amounts related to their mass and the rate at which they are accreting new material onto themselves. So a low mass, accreting object would be very faint.

Evidence for such tiny, dim objects exists. The first discovery of a very dim object (called L1014-IRS) forming inside what was previously thought to be a “starless core” in early Spitzer images was made by c2d team member Chadwick Young of Nicholls State University, and collaborators and announced in November 2004. Now, c2d team members have found about a dozen very faint objects that may be brown dwarfs in this earlier disk phase, embedded in cores of gas and dust. Once again, this shows that L1014-IRS, like OTS 44, is not an oddball, but the norm.

The new examples were found by c2d team members Tyler Bourke, Tracy Huard, and Philip Myers of the Harvard-Smithsonian Centre for Astrophysics; Michael Dunham of UT-Austin; and Jens Kauffmann of the Max-Planck-Institut für Radioastronomie. These findings suggest a new class of objects is emerging. Dubbed “Very Low Luminosity Objects,” or “VeLLOs,” they have less than one-tenth the Sun’s luminosity.

These are unlikely to be stars in a very early stage of formation.

"Accreting protostars are much more luminous than they will be when they become stars. So finding such a low luminosity in these objects is surprising. It implies that the product of the current mass and the rate at which mass is being added is unusually low"- Neal Evans

These studies show that the VeLLOs embedded in what were thought of as “starless cores” may be earlier stages of the disk-surrounded brown dwarfs found by Katelyn Allers and her c2d collaborators. In fact, further studies by Bourke and Huard show strong evidence for a disk around L1014-IRS, as announced in October 2005.
Cores to Disks” is one of six Spitzer Legacy Science Projects selected in November 2000 to complete major surveys with Spitzer. The c2d team was awarded 400 hours of Spitzer observations, and produces data freely available to all astronomers.

Source

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Posts: 131433
Date:
RE: Brown Dwarfs
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Edge-on Disk around a Brown Dwarf.

Researchers have recently discovered a young brown dwarf in the Taurus star-forming region that exhibits several characteristics (very faint for its spectral type, forbidden emission lines, anomalous near-IR colours) that are often observed in stars occulted by edge-on circumstellar disks.

The researchers propose to determine if an edge-on disk is indeed present by obtaining high-resolution images of this brown dwarf with ACS/HRC on the Hubble Space Telescope. If the disk is detected, they will constrain its physical properties, particularly its diameter, by fitting the images with the predictions of their models of brown dwarfs occulted by circumstellar disks.
These observations could potentially provide the first direct measurement of the size of a disk around a brown dwarf, which would comprise a fundamental test of models for the formation of these objects (e.g., embryo ejection).

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The 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. Spitzer has given us the possibility to study how planets are built in widely different environments" - Dr. Dániel Apai, astronomer at the University of Arizona, Tucson, and member of the NASA Astrobiology Institute's Life and Planets Astrobiology Centre.

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. This is exciting because we weren't sure if the disks of such cool objects would behave the same way that stellar disks do" - Dr. Ilaria Pascucci, co-author also of the University of Arizona.

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


This graph of data from NASA's Spitzer Space Telescope shows the spectra (middle four lines) of dusty disks around four brown dwarfs, or "failed stars," located 520 light-years away in the Chamaeleon constellation. The data suggest that the dust in these disks is crystallizing and clumping together in what may be the birth of planets.

Spectra are created by breaking light apart into its basic components, like a prism turning sunlight into a rainbow. Their bumps represent the "fingerprints" or signatures of different minerals.
Here, the light green vertical bands highlight the spectral fingerprints of crystals made up primarily of a green silicate mineral found on Earth called olivine. As the graph illustrates, three of the four brown dwarfs possess these microscopic gem-like particles. For comparison, the spectra of dust between stars (top) and the comet Hale-Bopp (bottom) are shown. The comet has the tiny crystals, whereas the interstellar dust does not.
The broadening of these spectral features or bumps -- seen here as you move down the graph -- indicates silicate grains of increasing size.
Another analysis of this same data shows that some of the brown dwarfs' dusty disks flare in their outer regions, while others are flattened. This flattening is correlated with increasing grain size, and probably occurs because the heavier dust grains are settling downward.

Together, these observations -- of crystals, growing dust grains and flattened disks -- provide strong evidence that the dust around these brown dwarfs is evolving into what might become planets. Prior to the findings, these first steps of planet formation were seen only in disks around stars, the brighter and bigger cousins to brown dwarfs.

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.

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