Solar System and the Universe

1. Solar System and the Universe

2. Temperature • Mass Common Characteristics of Stars

3. Most appear white to our eyes. (Not really their color) • Most stars have a predominant color that is dependent upon their surface temperature. • The hotter the star, the more blue light it emits. • Cooler stars emit more red light. • The predominant “color” can also be outside of the visible range of wavelengths, for very hot (> 20,000K) or very cool (<4500K) stars. If different colors are emitted with each about the same intensity, the star will appear white; this can occur for stars whose surface temperature is moderate. Temperature of a Star

4. The mass of a star determines how the star changes, including its rate of change and ultimate demise. • Stellar masses are compared to that of the Sun, rather than using kilograms. The Sun is 1 MSun (“one solar mass”). • The mass of the star will influence most of its other properties, including diameter, temperature, and lifespan. Mass

5. A star’s mass determines the strength of its gravitational attraction • Influences the temperature and density at the core of the star. • Will impact the rate at which hydrogen is fused into helium thus determining the star’s lifespan. • Most massive stars exist for the shortest amount of time, while the low-mass stars can last hundreds or even thousands of times longer. • Our Sun is expected to have a main sequence lifespan (when it is fusing hydrogen into helium) of 10 billion years. • A star with a mass of 15 MSun has a main sequence lifespan of only 15 million years, whereas a star with 0.5 MSun has a main sequence lifespan of 200 billion years. Mass

6. The star’s mass will also determine how it will “die.” • Planetary nebula and white dwarf (in the case of low mass stars), or as a supernova which leaves behind a neutron star or black hole (the most massive stars). • Humans have not been able to observe stellar evolution directly, of course: rather, computer and theoretical models are supported by observations of thousands of individual stars. Mass

7. A star’s diameter is also determined by its mass • More massive stars, during their main sequence period, have larger diameters. • Luminosity: determined by diameter and temperature together • Total amount of energy emitted by the star every second. • The luminosity of stars ranges from about 0.0001 to more than 100,000 solar units (or LSun). • We cannot measure luminosity directly – how bright the star appears to us depends upon its distance as well as its luminosity. Diameter & Luminosity

8. Before Main Sequence • Main Sequence • Hydrostatic equilibrium • Red Giant • White Dwarf • Possibly Black Dwarf Lifespan of a Star

9. Nuclear Fusion and Energy

10. Telescopes observe light and it is through this light that scientists gather all their information about the universe beyond Earth. • Space-based observatories (ex. Hubble Space Telescope). Provided an unimpeded view of the universe without Earth’s atmosphere acting as a filter. Indeed, some light frequencies, such as infrared, x-ray, and gamma ray, are only observed from space (or high in Earth’s atmosphere) because these frequencies do not penetrate to Earth’s surface. Technology & the Universe

11. Radio telescopes: detect radio waves (not sound), which are a low frequency form of light. Black holes and neutron stars create such intense magnetic field lines and radio telescopes have been instrumental in our understanding of these phenomena. Technology & Universe

12. Stars similar in mass to the Sun convert hydrogen into helium in their centers during the main-sequence phase, but eventually there is not enough hydrogen left in the center for fusion to provide the necessary radiation pressure to balance gravity. • The center of the star contracts until it is hot enough for helium to be fused into carbon. The hydrogen in a shell continues to convert to helium, but the outer layers of the star have to expand to conserve energy • Turns into a red giant until the carbon converts into heavier elements, energy dies and becomes a white dwarf, then possibly a black dwarf. Star Evolution

13. Universe Expansion