![]() ![]() D) The rotation rate increases and results in a disk of material around a protostar. 18) What is the minimum temperature for a cloud to excite emission lines from H2?Į) 1000 K C) 100 K 19) When is thermal energy trapped in the dense center of a cloud?Ī) when the gravity becomes so strong that photons cannot escapeī) when excited molecules collide with other molecules before they can release a photonĬ) when the cloud becomes so hot and dense that nuclear fusion beginsĭ) when magnetic fields trap the radiationĮ) when the cloud cools down so much that less light escapes than is produced by contraction B) when excited molecules collide with other molecules before they can release a photon 20) What happens to the rotation of a molecular cloud as it collapses to form a star?Ī) The rotation rate remains the same and results in stellar rotation.ī) The rotation dissipates and any residual is left in small overall rotation of the star.Ĭ) The rotation rate increases and results in fast rotation of the star.ĭ) The rotation rate increases and results in a disk of material around a protostar.Į) The rotation increases the speed of collapse and produces more massive stars. A) Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse. ![]() 17) Why do we think the first generation of stars would be different from stars born today?Ī) Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse.ī) Without heavy elements, the nuclear reactions at the center of the stars would be very different.Ĭ) Without heavy elements, there was no dust in the clouds and they collapsed faster.ĭ) The Universe was much denser when the first stars were born.Į) There were no galaxies when the first stars were born. C) The first generation stars were all very massive and exploded as supernova. 14) What property of a molecular cloud does not counteract gravitational contraction?ĭ) fragmentation D) fragmentation 15) How do astronomers infer the presence of magnetic fields in molecular clouds?Ī) by measuring the amount of interstellar reddeningī) by measuring the Doppler shifts of emission lines from gas clumps in the cloudĬ) by measuring the infrared light emitted by the cloudĭ) by measuring the polarization of starlight passing through the cloudĮ) by measuring the amount by which gravity is reduced D) by measuring the polarization of starlight passing through the cloud 16) What is the likely reason that we cannot find any examples of the first generation stars?Ī) The first generation stars are too faint to be visible now.ī) The first generation stars formed such a long time ago that the light from them has not yet had time to reach us.Ĭ) The first generation stars were all very massive and exploded as supernova.ĭ) The first generation stars formed with only H and He and therefore have no spectral features.Į) We do not know how the first generation stars were formed. D) more massive than a hundred times the Sun. 13) Calculations show that gravity begins to overcome thermal pressure in clouds that areĭ) more massive than a hundred times the Sun.Į) more massive than a thousand times the Sun. C) Thermal energy is converted to radiative energy via molecular collisions and released as photons. ![]() 12) What prevents the pressure from increasing as a cloud contracts due to its gravity?Ī) As the cloud becomes denser, gravity becomes stronger and overcomes the pressure buildup.ī) The pressure is transferred from the center of the cloud to its outer edges where it can dissipate.Ĭ) Thermal energy is converted to radiative energy via molecular collisions and released as photons.ĭ) Excess pressure is released in jets of material from the young stars.Į) Once the cloud reaches a critical density, the pressure becomes degenerate and independent of temperature. 11) The gravitational force in a molecular cloud depends onĮ) thermal pressure. ![]()
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