Exam 3 Version 3
Solutions
| (1) | C | The recently-launched Spitzer infrared telescope. |
| (2) | E | iron |
| (3) | A | 1 - 3 solar masses |
| (4) | E | Luminosity versus temperature |
| (5) | B | The change in energy output and temperature with time. |
| (6) | C | Within the dense cores of stars. |
| In the Big Bang, elementary particles condensed to form protons and neutrons, some of which fused into helium. All of the heavier elements, such as oxygen, carbon, iron, etc, were forged in the cores of stars, then dispersed into space when those stars exploded. |
| (7) | B | Helium |
| (8) | B | The Earth (~ 10,000 km). |
| (9) | C | Molecular clouds |
| Stars form when gas & dust cools and collapses under the influence of gravity. Gas & dust clouds evolve from a low density to higher densities. As the density increases, most of the gas collects into molecules. When looking for star forming regions in the nearby galaxy, astronomers always find dense lumps of molecular gas and dust in those regions. |
| (10) | B | Nuclear fusion reactions begin to occur in its core. |
| (11) | D | The expelled atmosphere of a dying star. |
| Planetary nebula are rings of gas surrounding a dying star. Their name was applied early in the history of telescopic astronomy, when these fuzzy rings, seen through small telescopes, had the appearance of small planets. The gas in a planetary nebula is the outer layers of a Sun-like star, gradually expanding away from the exposed core. |
| (12) | E | The dust particles dim and redden starlight. |
| (13) | C | relationships between physical characteristics of stars |
| (14) | A | The fainter star is the less massive star. |
| (15) | A | Only a small, rotating object is thought to be able to emit precisely timed pulses of radio radiation which are observed from pulsars. |
| (16) | E | An implosion followed by core rebound and explosion of a massive star. |
| (17) | B | brown dwarfs |
| (18) | A | Hot stars and interstellar gas. |
| (19) | E | A nebula |
| (20) | C | Open clusters contain tens to hundreds of mostly main-sequence stars. |
| (21) | A | High mass stars generate more energy and its core eventually collapses. |
| (22) | C | An accretion disk |
| (23) | E | By ejecting its outer layers, while the core becomes a white dwarf. |
| (24) | C | Stellar masses |
| (25) | E | smaller and hotter |
| (26) | A | Neutron star |
| (27) | A | Much of the emission is due to hydrogen which has a strong red line. |
| (28) | D | About one second. |
| At the end of their lives, massive stars form an iron core by fusing silicon. The iron core forms in just a few days. Fusion ends at this point. The core has a mass of about twice the mass of the Sun. The iron core cannot support itself and collapses, from a size of several thousand kilometers to a few kilometers. The rest of the star, which contains most of the star’s mass, implodes onto the core in a matter of a few seconds. |
| (29) | E | 5 billion years |
| (30) | E | Hydrogen atoms |
| (31) | A | A white dwarf in a binary system |
| (32) | C | Hydrogen and helium |
| (33) | D | 50 million years |
| (34) | D | A supernova explosion after the collapse of a massive star. |
| (35) | E | Within dense, dusty clouds. |