Astrophysicists uncover secret origin of brown dwarfs

[David]

http://phys.org/news/2012-04-astrophysicists-uncover-secret-brown-dwarfs.html

Astrophysicists uncover secret origin of brown dwarfs
April 26, 2012

The origin of brown dwarfs is one of the great unsolved mysteries
facing astrophysicists today. In a new study published in The
Astrophysical Journal, Western’s Shantanu Basu and University of
Vienna’s Eduard Vorobyov present a new model of brown dwarf formation
that unites the best parts of existing theories and has far-reaching
implications for understanding the population of low mass objects in
the universe.

Brown dwarfs are astronomical objects that have too little mass to be
called stars and too much mass to be called planets. Only a
theoretical concept until discovered in the mid-1990s, several hundred
brown dwarfs have now been identified through infrared telescopes and
surveys.
“There could be significant mass in the universe that is locked up in
brown dwarfs and contribute at least part of the budget for the
universe’s missing dark matter,” said Basu, a professor in Western’s
Department of Physics and Astronomy. “And the common idea that the
first stars in the early universe were only of very high mass may also
need revision.”
One leading theory suggests that brown dwarfs form like stars through
the direct collapse of low mass interstellar gas cloud fragments while
another speculates that they are formed after the collapse of more
massive cloud fragments yield multiple bodies including brown dwarfs
that are ejected due to the mutual interaction of the bodies. Both
scenarios produce conceptual and theoretical problems and are equally
challenged and supported by scientists.
Employing numerical hydrodynamic simulations – carried out in part by
utilizing the high performance computing capabilities of Western's
SHARCNET – Basu and Vorobyov show the evolution of the swirling
nebular disc of gas around a newly formed protostar (or a star that is
still forming) is critical to brown dwarf formation. Such a disc of
gas has long been postulated to exist around the early Sun and the
planets in the Solar System are thought to have condensed out of such
a disc.
In the study, Basu and Vorobyov prove that the early life of a disc is
characterized by the formation of multiple fragments that orbit the
central protostar and that the interaction of fragments leads to the
ejection of some brown dwarf fragments that have yet to fully form.
The ejection speeds in this mechanism are much lower than in a model
where ejections occur only for fully formed brown dwarfs and provide a
more favorable comparison with observations that show that brown
dwarfs are present in close proximity to young stars.
Provided by University of Western Ontario (news : web)

[Andy Z]

My guess is that interstellar space is literally swarming with brown dwarf objects of all shapes ans sizes, mostly old and dark. These objects are likely to outnumber the stars in the galaxy many times over, and that this massive population of dark objects explains how the Sun was able to capture its own sub-brown dwarf object - in effect, it became a statistical probability that each star captures one or more of these objects eventually.
 
Anyhow, here's another item today that indicates how dwarf planets from the Kuiper Belt and beyond took part in a 'reorganisation' of the solar system some hundreds of millions of years after the Sun's formation.  Saturn's moon Phoebe appears to have been just such an object, captured by the gas giant into a retrograde orbit.  This seems entirely consistent with the Celestial Battle as described by Sitchin, an event likely to be coincident with the 'Late, Heavy Bombardment' 3.9 billion years ago:
 
News feature: 2012-119                                                                     April 26, 2012
Cassini Finds Saturn Moon has Planet-Like Qualities
The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-119&cid=release_2012-119
PASADENA, Calif. -- Data from NASA's Cassini mission reveal Saturn's moon Phoebe has more planet-like qualities than previously thought.
Scientists had their first close-up look at Phoebe when Cassini began exploring the Saturn system in 2004. Using data from multiple spacecraft instruments and a computer model of the moon's chemistry, geophysics and geology, scientists found Phoebe was a so-called planetesimal, or remnant planetary building block. The findings appear in the April issue of the Journal Icarus.
"Unlike primitive bodies such as comets, Phoebe appears to have actively evolved for a time before it stalled out," said Julie Castillo-Rogez, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Objects like Phoebe are thought to have condensed very quickly. Hence, they represent building blocks of planets. They give scientists clues about what conditions were like around the time of the birth of planets and their moons."
Cassini images suggest Phoebe originated in the far-off Kuiper Belt, the region of ancient, icy, rocky bodies beyond Neptune's orbit. Data show Phoebe was spherical and hot early in its history, and has denser rock-rich material concentrated near its center. Its average density is about the same as Pluto, another object in the Kuiper Belt. Phoebe likely was captured by Saturn's gravity when it somehow got close to the giant planet.
Saturn is surrounded by a cloud of irregular moons that circle the planet in orbits tilted from Saturn's orbit around the sun, the so-called equatorial plane. Phoebe is the largest of these irregular moons and also has the distinction of orbiting backward in relation to the other moons. Saturn's large moons appear to have formed from gas and dust orbiting in the planet's equatorial plane. These moons currently orbit Saturn in that same plane.
"By combining Cassini data with modeling techniques previously applied to other solar system bodies, we've been able to go back in time and clarify why it is so different from the rest of the Saturn system," said Jonathan Lunine, a co-author on the study and a Cassini team member at Cornell University, Ithaca, N.Y.
analyses suggest that Phoebe was born within the first 3 million years of the birth of the solar system, which occurred 4.5 billion years ago. The moon may originally have been porous but appears to have collapsed in on itself as it warmed up. Phoebe developed a density 40 percent higher than the average inner Saturnian moon.
Objects of Phoebe's size have long been thought to form as "potato-shaped" bodies and remained that way over their lifetimes. If such an object formed early enough in the solar system's history, it could have harbored the kinds of radioactive material that would produce substantial heat over a short timescale. This would warm the interior and reshape the moon.
“From the shape seen in Cassini images and modeling the likely cratering history, we were able to see that Phoebe started with a nearly spherical shape, rather than being an irregular shape later smoothed into a sphere by impacts," said co-author Peter Thomas, a Cassini team member at Cornell.
Phoebe likely stayed warm for tens of millions of years before freezing up. The study suggests the heat also would have enabled the moon to host liquid water at one time. This could explain the signature of water-rich material on Phoebe's surface previously detected by Cassini.
The new study also is consistent with the idea that several hundred million years after Phoebe cooled, the moon drifted toward the inner solar system in a solar-system-wide rearrangement. Phoebe was large enough to survive this turbulence.
More than 60 moons are known to orbit Saturn, varying drastically in shape, size, surface age and origin. Scientists using both ground-based observatories and Cassini's cameras continue to search for others.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for the agency's Science Mission Directorate in Washington. The California Institute of Technology in Pasadena manages JPL for NASA.
For more information on the Cassini mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .
Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jcc...@jpl.nasa.gov
Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne....@nasa.gov

 



Many thanks,

Andy Lloyd

Author and artist,

http://www.darkstar1.co.uk

http://cheltenham-art.com/andylloyd.htm
 
http://www.andylloyd.org

http://www.modelmayhem.com/member.php?id=440880



 

> Date: Thu, 26 Apr 2012 11:01:15 -0700
> Subject: Astrophysicists uncover secret origin of brown dwarfs
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