Brown Dwarfs are Black-Sheep of the Family

University of Colorado at Boulder; July 2, 2001; Press Release: "Brown Dwarfs are stellar embryos evicted by siblings, according to study" 

European Southern Observatory; June 7, 2001; Press Release: "NTT Observations Indicate that Brown Dwarfs Form Like Stars" 

Chart of Brown Dwarfs in Trapezium area of the Orion Nebula.  ESO.

Brown Dwarfs are the runts of the stellar litter. That's the conclusion that University of Colorado at Boulder astronomer Bo Reipurth and Cathie Clarke of the Institute of Astronomy in Cambridge, England, reached in a paper published in The Astronomical Journal for July 2001. This research is another piece of evidence that the mysterious Brown Dwarfs, recently discovered to inhabit the Orion Nebula in great number, begin life evolving like stars, as opposed to forming like gas giant planets.

Stars are formed in clouds of gas, composed of material falling inward toward the core, under the force of gravity. Embryonic stars form in the cores; those in the center accrete and grow rapidly. This often results in multi-star systems. "Most stars in our Milky Way Galaxy began either as binary or multiple-star systems, and soon after birth a tug-of-war starts between stellar embryos over which ones can accumulate the most star-forming material," explains Reipurth.

Brown Dwarfs are objects that did not accrete enough material to cause the gravitational compression required for nuclear reactions to commence -- in essence they are failed stars. A body must attain about 8% the mass of our Sun in order to start the nuclear ignition process. While tiny, compared to the Sun, Brown Dwarfs can reach the size range of 10 to 70 Jupiters. The only light they give off is heat radiation in the infrared -- at most this light is 100-times fainter than our Sun. Many Brown Dwarfs have been discovered "free-floating" in the Milky Way recently, and astronomers have wondered why the Brown Dwarfs are not found in association with normal stars.

The new research explains why: "Amazingly, calculations show that the gravitational horseplay between stellar embryos almost always end up with the lightest member being violently flung out of the little group," says Reipurth. So, the Brown Dwarf not only suffer from "not getting enough to eat" but the added indignation of being flung out from its group of siblings: it is the 'runt' of the litter. Dwarfs are constantly flung away from their accreting family members and usually end-up drifting completely out of the system.

This paper and recent observational evidence creates a distinction between giant extrasolar planets and Brown Dwarfs. Unlike the Dwarfs, the identified giant exo-planets are frequently close companions of a star, indicating that they evolved in the protoplanetary disk around a star and not at the disk center like a star.

Infrared-sensitive instrument at the European Southern Observatory (ESO), 3.5-m, New Technology Telescope at the La Silla Observatory have detected Brown Dwarf candidates in the Trapezium cluster, at the center of the Orion Nebula. Protoplanetary disks surrounding many of the suspected Brown Dwarfs confirm they are newly formed and indicate that these objects initially form like stars. This is the largest population of Brown Dwarfs known so far.  At left is a chart of the Trapezium area of the Orion Nebula, indicating the location of Brown Dwarfs.  Those with protoplanetary disks are indicated by double open circles, those without disk have a single circle.  Click chart to see surrounding area and comparison infrared image.  Chart supplied by ESO.

Holy 'Sat' Tax!

Reuters; July 11, 2001; Newswire: "Los Angeles tries to tax satellites"

"My job is to make sure all property that's taxable gets assessed and I'm going to follow the law. If the law says its not taxable it's not taxable. If it is taxable I will assess it," states Los Angeles County Assessor Rick Auerbach. So when Auerbach determined that Huges Electronics Corporation, based in Los Angeles, had eight previously un-assessed items of property -- valued at $100-million each -- he tried to slap a property tax on them.

George Jamison, a Hughes vice president, was not amused. "It's ludicrous, absolutely," he said. "It's the type of issue, quite frankly, that causes the company to consider relocating its base of operations to a more business-friendly environment."

So, is this just another example of a big corporation flexing its economic muscles to avoid paying taxes? Maybe not. For the properties that Auerbach wants to tax are 35,890-km above the Earth, in geostationary orbit: County Assessor Auerbach wants to tax Huges' communications satellites. After researching the issue, he concluded that the satellites are taxable as "movable property," currently out of state, just like construction equipment.

Huges complained to the California State Board of Equalization about the tax. After presentations by Huges and Auerbach, the board sided with Huges and voted 5-0 to "fast track" a rule that satellites cannot be taxed. "We think the ruling is important," Jamison said. "These spacecraft are not to be in the state of California, have never been in the state of California during their useful lives and will never be in the state of California in the future."

Auerbach is not deterred by the ruling and is ready to take his argument to the highest court in the land. "I'll have to see what basis they have for the rule," Auerbach said. "If I believe it's improper (under the) U.S. Constitution and state statutes my option is to go to Superior Court."

Moon Chips, Anyone?

Observatoire de la Cote d'Azur; July 10, 2001; Press Release: "The Irregular Satellites: Chips Off Older Blocks" 

CNN.com; July 11, 2001; Space: "Saturn hangs on to title as moon king"

Saturn irregular moon S/2000 S2 is arrowed in this multi-image photo.  ESO image.

 As previously reported in the NewsNotes (01.15.01: "New Moons Rise") Brett Gladman, of the Observatoire de la Cote d'Azur in Nice, France, and his international team uncovered a dozen previously unknown "irregular" moons around Saturn at the end of last year. These moons are considered irregular because their sizes and orbits (5-40-km diameter, with distant, non-circular orbits highly-inclined to the planet) indicate they were not part of the Saturnian system when the planet initially formed. The team has now had time to track these moons and use their newly determined orbits to speculate on their origins. Their theory of irregular moon formation is valid for the gas giant planets.

When parameters for the moons are examined, their orbits are found to fall into related groups. Relative orbital speed differences between the single largest and related smaller moons indicate that the latter are "chips" of the former. This evidence, published in the July 12 issue of Nature, is used to assert the following irregular moon formation theory:

When the gas giant planets formed 4.5-billion years ago, a huge "cocoon" of gas enveloped them.
Small bodies, in orbit around the Sun, were slowed by passage through this cocoon. The smallest objects were slowed enough to spiral into the planet. Large bodies had enough momentum to continue on without getting captured. As a result, moons in the 10 to 100-km range were favored to remain in orbit around the planet.
Eventually the cocoon dissipated and no new moons could be captured by this method.
Passing comets and asteroids broke-up the captured bodies into smaller moons. Because the cocoon has dissipated, small moons did not suffer the fate of spiraling into the parent planet.

Currently, Saturn reigns supreme in our Solar System with 30 moons total. The moon scores for the other gas giant planets has Jupiter at 28, Uranus 21, and Neptune at just 8.  The Gladman team may soon reveal more moons around these planets when they resume observations this August.  Gladman thinks Jupiter will eventually surpass Saturn in the standings: "Because Jupiter is closer we can see smaller moons.  So I think Jupiter is going to win in sheer number because you can see a lot of little ones that are invisible at Saturn."

Something Was Rotten in the Solar System

Geological Society of America; June 27, 2001; Press Release: "A disturbance in the 'force' caused the K-T impact?"

The theory that something whacked the Earth 65-million years ago and wiped out the dinosaurs (along with most other living things) has generally come to be accepted. The evidence for a worldwide calamity is in the geologic record, revealed in a layer of clay at the Cretaceous/Tertiary (K-T) boundary of sedimentary deposits. Now, one group of UCLA researchers thinks the catastrophe was part of a Solar System-wide event.

According to Bruce Runnegar, Director of UCLA's Center for Astrobiology: "In order to better understand the history of the inner Solar System over hundreds of millions of years, we carried out several accurate, long-term, numerical simulations of the orbits of the nine major planets using physical models with increasing complexity. Our best calculations show that the dynamical state of the inner Solar System changed abruptly about 65 million years ago."

This unexplained disturbance changed the orbits of the inner planets and perturbed asteroids into Earth-crossing orbits. While scientists don't yet know exactly what the colliding body was composed of, this evidence of an abrupt change in Solar System dynamics might help deduce the composition of the body.

These findings were presented at the Earth Systems Processes conference, Edinburgh, Scotland, last June.