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Posted on 08/21/2002 1:46:27 AM PDT by Snow Bunny
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Hi everyone, thank you for your fantastic support of the Canteen. God bless you all and your families.
Thank you too for your support of our troops and their families.
Thank you Veterans!!!
Evolution of a Single, Low Mass Star from Molecular Cloud to Fusion and Planetary Accretion
Although dust and gases are found throughout interstellar space, star formation is a relatively rare event with perhaps only 10 percent of interstellar medium actually being converted into stellar mass. Interstellar space contains roughly about 10 hydrogen atoms per cubic meter at approximately 100 to 106 K. In pockets of non-homogeneous molecular gas and dust, the densities of matter may be as high as 104 to 106atoms per cubic meter (contrast this with atmospheric air at STP approximately 5.3 x 1025 atoms per cubic meter). Particulate matter within these regions is thought to include not only atomic and molecular hydrogen (H2), but also helium, carbon monoxide (CO), water ice (H2O), alcohols, ammonia (NH3), formaldehyde (HCHO), formic acid (HCOOH), methane (CH4), and other organics such as aliphatic hydrocarbons. Dust particles effectively block ultraviolet radiation from nearby stars, thus decreasing temperatures within these regions to only about 10 to 20 K.
Radio astronomers use CO emissions at 1.3 and 2.6 mm to identify molecular hydrogen (H2) in these cold molecular clouds. H I regions consist primarily of neutral atomic hydrogen (H) gas with densities of up to 107 atoms per cubic meter at temperatures around 100 K, and are detected from 21-cm emissions generated by the quantum spin flip of individual hydrogen electrons. H I regions may also be detected by Alpha Lyman H-absorption bands. In contrast, very hot H II and He III regions (up to 10,000 K) within glowing emission nebulae close to O and B spectral type stars (such as the Lagoon Nebula) are detected via infrared radiation
The accepted view of star formation requires that an influx of non-thermal energy (shock wave or turbulence) initiate the collapse of molecular clouds. However, some researchers believe that these clouds can become stellar nurseries simply because cooler temperatures allow matter to move more slowly, allowing tiny gravitational and ionic forces between atoms to form complex molecules, leading to gravitational collapse.
Irrespective of the initial mechanism, areas of accumulated matter grow and coalesce, eventually forming a center of mass around which particulate matter and gases orbit, often colliding with other particles or the center of mass itself. As the mass contracts under continuing gravitational attraction, the core begins to heat and infrared radiation is released. Rotational velocity also increases, conserving outward angular momentum while allowing a continuous inward flow of material. The orbiting mass begins to take on a flattened disk-like shape about the core, which is now more appropriately referred to as a prestellar core or protostar. The protostar may have densities of up to 107 atoms per cubic meter at this stage in its evolution (newly formed stars have observed densities of about1022 atoms per cubic meter). Interior core temperatures may reach 150,000 K, with surface temperatures of about 3500 K as outward thermal pressure increases to compensate for the inward pull of gravity. At this point, the protostar will appear on a Hertzsprung-Russell diagram as a cool but bright star, as luminosity is still dependant upon gravitational collapse.
As contraction continues, particles that are outside the accretion disk, but still under the influence of gravitational attraction from the protostar, will be drawn into more extreme sinusoidal orbits in and out of the plane of the accretion disk. The chance that these extra accretion disk particles will collide with particles within the disk increases not only with increased density and thickness of the disk, but also with a decreased angle of incidence relative to the plane of the disk. Most particles will ultimately become part of the protostar, but some will enter into a variety of orbits within the accretion disk plane depending on their relative velocities, often forming additional regions or bands of increased density from which protoplanets may later accrete.
While the protostar stage of development may only take a few years, the pre-main sequence stage may take tens of millions of years because continued contraction, accretion and heating of the stellar core proceeds slowly.
Early pre-main sequence stars are often referred to as T Tauri stars. In these very young stars, an excess of ultraviolet radiation is released as dipolar magnetospheric accretion columns form, slowing the rotational velocity of the star in relation to the disk, and transferring mass directly from the disk to the poles of the young star. Accretion rates for these stars have been estimated to be from about 2 x 10-8 to 10-7 the mass of our Sun per year. However, mass is also simultaneously ejected from these stars perpendicular to the circumstellar disk along magnetic field lines in very narrow bipolar jets or pulses of material, possibly a mechanism for reducing excess angular momentum. T Tauri stars are hotter but not as bright as protostars, and will appear on a Hertzsprung-Russell diagram closer towards the main sequence as late F through early K spectral types.
Once the internal temperatures of the young star reach about 1 million Kelvin, the proton-proton chain reaction begins, first fusing two protons into one deuterium plus a positron and a neutrino [equation 1].
[1] 1 H + 1 H yield 2 H + positron (e+) + neutrino
The positron almost immediately encounters an electron, and the particles annihilate each other, producing two gamma rays. These gamma rays will ultimately migrate to the stellar surface where they will each be emitted as about 200,000 photons of visible light [equation 2].
[2] e+ + e- yield 2 gamma rays
Deuterium created via the reaction represented by equation 1 reacts with a proton to create one helium-3 plus another gamma ray [equation 3].
[3] 2 H + 1 H yield 3 He + gamma ray
When stellar core temperatures reach 10 million Kelvin, two helium-3 atoms will be fused into one helium-4 atom plus two protons [equation 4], an event that marks the transition to the main-sequence phase of stellar evolution, when energy produced is no longer due to gravitational collapse, but by nuclear fusion.
[4] 3 He + 3 He yield 4 He + 2 1 H
Main sequence stars are typically very stable because of hydrostatic equilibrium, where the forces between continued gravitational collapse equal internally generated thermal pressures. Typically, a low-mass star will continue in the main sequence for about 90% of its lifetime, slowly converting hydrogen into helium for several hundred million to several billion years until the supply of hydrogen is exhausted.
Thank you all for you thoughts and prayers! :-)
Michael
Good morning, Snow! Good morning, EVERYBODY!
HAPPY HUMP DAY !!
CLARA! SASSY! CLARA! SASSY!
.......hehehehe............giggle........giggle.......
Today's classic warship, USS Milwaukee (CL-5)
Omaha class light cruiser
Displacement: 7,050 t.
Length: 555’6”
Beam: 55’4”
Draft: 13’6”
Speed: 34 k.
Complement: 458
Armament: 12 6”; 4 3”; 10 21” torpedo tubes
Commissioned on 20 June 1923
Sold for scrap on 10 December 1949
The USS MILWAUKEE (CL-5) was laid down 13 December 1918 by Seattle Construction & Dry Dock Co., Seattle Wash.; launched by Todd Dry Dock & Construction Co. Seattle, Wash., 24 March 1921; sponsored by Mrs. Rudolph Pfeil; and commissioned 20 June 1923, Capt. William C. Asserson in command.
Shakedown took the new cruiser to Australia via Hawaii, Somoa, Fiji Islands, and New Caledonia, for the Pan-Pacific Scientific Congress which opened in Sydney 23 August 1923. Fitted with the finest sonic depth-finding equipment, MILWAUKEE gathered knowledge of the Pacific en route.
Although she served primarily in the Pacific during the decades between the world wars, the highlights of her peacetime service came in the Caribbean. On 24 October 1926, MILWAUKEE and GOFF (DD-247) arrived at the Isle of Pines from Guantanamo Bay to assist victims of a fierce hurricane which had devastated the island 4 days before. The American ships established a medical center at the city hall in Nueva Gerone, furnished the stricken area over 50 tons of food, replaced telephone lines which had been swept away, and maintained wireless communication with the outside world. The efficient and tireless labors of the crews won the respect and gratitude of everyone in the area.
Over a decade later, while steaming north of Hispaniola and Puerto Rico, 14 February 1939, MILWAUKEE recorded the greatest depth yet discovered in the Atlantic, 5,041 fathoms, or 30,246 feet. The spot has thenceforth been designated "Milwaukee Depth."
Totalitarianism was then threatening to shatter world peace and to snuff out freedom. Over a year before, Japanese military hotheads had bombed U.S. gunboat PANAY (PR-5) in the Yangtze River near Hankow, China, 12 December 1937, testing American determination to remain in the Orient. MILWAUKEE, as part of the U.S. Navy's response to the challenge, got underway from San Diego 3 January 1938 on a cruise to the Far East, which took her to Hawaii, Samoa, Australia, Singapore, the Philippines, and Guam. As tension abated she returned home 27 April.
The new breed of dictators needed a more forceful lesson. Late in the summer of 1939, Hitler invaded Poland, plunging Europe into war. Somewhat over 2 years later, Japan attacked Pearl Harbor, drawing the United States into the conflict.
MILWAUKEE, Capt. Forest B. Royal, was in New York Navy Yard for overhaul when Japan struck. Departing New York 31 December 1941, MILWAUKEE escorted a convoy to the Caribbean and arrived Balboa 31 January 1942, transited the Panama Canal, and escorted eight troop transports to the Society Islands. Returning to the Atlantic through the canal 7 March, she stopped at Trinidad en route to Recife, Brazil, where she joined the South Atlantic Patrol Force.
For the next 2 years, MILWAUKEE made repeated patrols from ports of Brazil, steaming from the border of French Guiana, down to Rio de Janeiro, and across the Atlantic Narrows almost to the African coast. On 19 May 1942, while steaming from Ascension Island toward Brazil, she received SOS signals from SS COMMANDANTE LYRA and sped to the assistance of the Brazilian merchantman, torpedoed by a German U-boat off the coast of Brazil. On reaching the scene that morning, MILWAUKEE found COMMANDANTE LYRA abandoned, burning forward and aft, and listing to port.
Destroyer MOFFETT (DD-362) picked up 16 survivors and MILWAUKEE rescued 25 others, including the ship's master. Cruiser OMAHA (CL-4) and destroyer McDOUGAL (DD-358) were soon on the rescue scene. While MILWAUKEE refueled at Recife, OMAHA’s salvage party jettisoned deck cargo and ready ammunition for deck guns from the burning Brazilian merchantman. MILWAUKEE immediately returned to the scene. Her salvage party jettisoned cargo to lighten the Brazilian. The fires were brought under control as COMMANDANTE LYRA was towed towards Fortaleza, Brazil, arriving 24 May.
MILWAUKEE put out of Recife 8 November 1942 in company with cruiser CINCINNATI (CL-6) and destroyer SOMERS (DD-381) seeking German blockade runners. On 21 November 1942, the task force encountered a strange ship which turned out to be the German blockade runner ANNALIESE ESSENBERGER. MILWAUKEE challenged the unidentified ship who replied with the call letters L-J-P-Y, the international call of Norwegian freighter SJHFLBRED. The Allied secret identification signal brought no reply. The two American cruisers maneuvered to cover destroyer SOMERS chasing the enemy into a small rain squall. At 0651, when SOMERS had closed to 4 miles, smoke and flames poured from the enemy who lowered boats. Minutes later the first of three tremendous explosions hurled wreckage hundreds of feet in the air and the freighter settled by the stern. Then the Norwegian flag was hauled down and the German merchant swastika flag was raised at the main. The German motorship heeled over to port and sank by the stern. MILWAUKEE took aboard 62 prisoners from four liferafts.
On the morning of 2 May 1943, while MILWAUKEE was under repairs at Recife, her crew showed great initiative and skill fighting a fire on tanker SS LIVINGSTON ROC which threatened the harbor.
MILWAUKEE continued her South Atlantic patrols until 8 February 1944 when she departed Bahia, Brazil, for the New York Navy Yard. She stood out from New York 27 February as a unit of the ocean escort for a convoy which reached Belfast, Northern Ireland, 8 March 1944. On 29 March 1944, MILWAUKEE put to sea, en route to Murmansk, Russia, with British Convoy JW58. A German submarine was sunk during the night. The following day enemy planes shadowing the convoy were shot down by fighter planes launched from HMS ACTIVITY. A wolfpack of German submarines tried to penetrate the convoy screen during the night of 31 March 1944 but was driven off. The following night, seven German submarines shadowed the convoy but they, too, were driven off with the possible loss of one enemy submarine. That morning carrier-based planes reported sinking a German submarine 10 miles astern.
On 4 April, four escorts of the Russian Navy joined the convoy now headed for Archangel. A few hours later, MILWAUKEE left the convoy and headed for Kola Inlet. There on 20 April 1944, the ship was transferred on loan to the Soviet Union under lend-lease. She commissioned in the Russian Navy as MURMANSK and performed convoy and patrol duty along the Atlantic sealanes throughout the remainder of the war. Transferred back to the United States 16 March 1949, MILWAUKEE, the first of 15 American warships returned by Russia, entered Philadelphia Naval Shipyard 18 March 1949, and was sold for scrapping 10 December 1949 to the American Shipbreakers, Inc., Wilmington, Del.
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