The Stages of Stellar Evolution

1. The Stages of Stellar Evolution

2. Starbirth - What is needed Kinda looks like a Middle finger. • Large molecular cloud ranging from 1 light year to 300 light years across • A density of about 10^7 molecules per square inch • A temperature range of –440 degrees F to 1000 degrees F • Each cloud could make up to 100,000 stars the size of our Sun

3. Formation of Molecular Clouds • The interstellar medium of the Galaxy is the space between the stars. It is not void, but filled with vast amounts of gas and dust. The ISM of a Galaxy has a mass of several billion times that of it’s stars. • Unlike the vast majority of this space, which are wide open frontiers containing but few atoms, some areas have densities about 1,000 times greater. In these spaces many atoms combine into molecules, and molecular clouds form from gas clouds. • Molecular clouds tend to form the colder part of the ISM, with temperatures as low as 10K. Molecular Cloud Barnard 68 Credit: FORS Team, 8.2-meter VLT Antu, ESO

4. Facts on Molecular clouds: Molecular clouds in our galaxy have diameters ranging from less than 1 to 300 light-years. These contain enough gas to form from about 10 to 10 million stars like our Sun. Molecular clouds that exceed the mass of 100,000 suns are called Giant Molecular Clouds. A typical full-grown spiral galaxy contains about 1,000 to 2,000 Giant Molecular Clouds and many more smaller ones. Molecular clouds were first discovered in our Milky Way Galaxy with radio telescopes about 25 years ago. Most of the gas within molecular clouds is about -440 degrees Fahrenheit. Since gas is more compact in a colder climate, it is easier for gravity to collapse it to form new stars. Due to these low temperatures, the same climate that is conducive to star formation also may shut off the star birth process. Sources include: http://antwrp.gsfc.nasa.gov/apod/ap990511.html http://oposite.stsci.edu/pubinfo/pr/1997/34/af2.html

5. Starbirth in Nebulae • Causes of Starbirth in Nebulae. • Nebulae are set in motion by a supernova shock wave, rocky body, change in magnetic fields, etc.

6. Pretty

7. THE PROTOSTAR A dense ball of gas and dust forms a protostar. Over time, accumulation of matter and compression of the core by gravity causes it to heat up. Heat radiates into the surrounding cloud, causing it to become bright.

8. Brown Dwarf Stars • Brown dwarfs are believed to exist throughout the galaxy. • They are too low mass to produce helium so they give off little light and are difficult to locate. • Basically they are giant Jupiter’s. http://www.spaceflightnow.com/news/n0008/24hstbrown/

9. Protoplanet Formation • The process of solar evolution was first described by Pierre Simon de Laplace. He believed that a nebula will contract under its own gravity creating a central star (nebular theory). The remaining material orbits the star and in time is flattened into a disk. The material in this disk forms protoplanets.

10. Protoplanets Clean up • Just as the central star in our system formed, the protoplanets too form from their own gravity. As the disk material orbits a star the tiny particles attract each other and form slightly larger object. As these planets-to-be grow, their ability to attract the surrounding gases increases so that in time the protoplanets will actually suck the newly formed solar system clean. Like condensation of a rain drop around a dust particle protoplanets sweep up the interstellar dust clouds as seen in this picture.

11. Existing Protoplanets • An existing protoplanet is shown here. Located in the constellation of taurus • For more information visit <http:www.Windows.Ucar.Edu> FAST FACTS: Star Name: TMR-1 (Taurus Molecular Ring, star 1 - binary) Planet name: TMR-1C Constellation: Taurus Coordinates: 4h39m15s RA, +25d53m Dec. Distance: 450 light-years Field of view: 19 arseconds

12. Pre-Main Sequence Stars • Pre-main sequence stars start when a protostar has formed and continues until the star reaches the main-sequence. • These stars radiate away head-energy, but also increase stellar temperature due to contraction. • Pre-main sequence stars also have negative head capacity. • Infared color arising from thermal dust emission are easily seen in sequence such as T-Tauri stars

13. A Bow Shock around a Young Star Young stars are very energetic, and may emit intense stellar winds or gusty flares. In this picture, one young star is probably being blasted by one of its siblings.

14. Specific Classes: OBAFGKM • A star’s size predestines (to a degree) its personality and lifespan. Stable adult Main Sequence stars are related by mass, heat, color, lifespan,burn-rate, size: • Spectral class O, B stars (rare, but very interesting): Giant, hot, bright, blue stars burn up quickly and die violently. Lifetime is only 1-10 million years. • Spectral class A,F,G,K stars (like the Sun): Middle of the road habits. Orange, yellow or white in color. Typically will live for 1-20 billion years. • Spectral class M,R,N, L stars: (most abundant): Small, cool, Red, and dim. Will burn the slowest and live the longest (about 50billion years).

15. Specific Classes: OBAFGKM • What makes up the stars greatly effects whether they are categorized as O, B, A, F, G, K, M, or L. This chart shows the general chemical make up of stars related to where they are placed on the spectral graph.

16. Examples of OBAFGKM Hottest Stars: T>30,000 K; Strong He+ lines; no H lines (or only very weak at O9). T=15,000 - 30,000 K; Strong neutral He lines; very weak H lines, getting stronger from B0 through B9. The ‘O’ class star. The ‘B’ class star.

17. Examples of OBAFGKM T=10,000 - 7500 K; Strongest H lines, Weak Ca+ lines emerge towards A9 types. T=7500-6000 K; H grows weaker through F9, Ca+ grows stronger, weak metals begin to emerge. The ‘A’ class star. The ‘F’ class star.

18. Examples of OBAFGKM T=5000-3500 K; Strong metal lines, weak CH & CN molecular bands begin to appear, growing through the class. H lines nearly gone. T=6000-5000 K; Strong Ca+, Fe+ and other metals dominate, H grows weaker through the class. The ‘G’ class star. The ‘K’ class star.

19. Examples of OBAFGKM Cool Stars: T ~2000 - 3500 K; strong molecular absorption bands particularly of TiO and VO emerge and strengthen, as do lines of neutral metals. Virtually no H lines anymore. The ‘M’ class star.

20. Red Dwarf Stars • These stars are the smallest, coolest, and faintest of all. • Because of this, they are difficult to view from Earth.

21. As a star runs out of hydrogen to fuse, its core collapses and sends a shock wave from the heat outward, expanding the outer layers of the star. The temperature and pressure conditions in the core increase enough to induce the fusion of heavier elements late in its life. Betelgeuse, pictured at left, is a red supergiant. It is nearing the end of its life and will soon become a supernova. Red Giants

22. Pulsating Variable Stars Pulsating variable stars vary in brightness because they pulsate in and out. In the outer layers of pulsating stars, the inward pull of gravity and the outward push of pressure are out of balance. When outward pressure overwhelms inward gravity, the star expands. However, when inward gravity surpasses outward pressure, the star contracts.

23. Pulsating variable stars pulse in size as well as temperature. small and hot big and cool The pulsations can be regular or irregular, ranging from more than a year to only a few hours between pulsations. The change in size by about 15% of their radius. For more info in Pulsating Variable Stars, you can visit: http://faculty.rmwc.edu/tmichalik/pulsvar.htm

24. Planetary Nebulae Planetary nebulae are formed when a red giant star ejects its outer layers as clouds of luminescent gas, revealing the dense, hot, and tiny white dwarf star at its core. Information can be found at:http://www.seds.org/billa/twn/ This is one of the most complex of the planetary nebulae. The HST images seem to indicate that the central star is actually a binary system and that the nebula we see today is actually the result of at least two separate events.

25. White Dwarf • White dwarf: A star that is the remnant core of a low mass star that has completed fusion in its core. The sun will become a white dwarf. White dwarfs are typically composed of carbon, have about the radius of the earth, and do not significantly evolve further.

26. White Dwarfs • A white dwarf is a whitish dead star having low luminosity, small size and very great density. These white dwarf stars are intensely hot ... but they are cooling. Their interior nuclear fires no longer burn, so they will continue to cool until they fade away. The white dwarfs are circled.

27. Supergiant • A supergiant is any star of very great intrinsic luminosity and relatively enormous size. • Several magnitudes brighter than a giant star and several times greater in diameter. • Their lifetimes are probably only a few million years long.

28. HD 65750 • This supergiant is located in the center of nebula to the left. The nebulosity around the star is the result of light reflected by dust surrounding it. The dust consists mainly of silica condensed from material which the star is losing from its surface at a fairly steady rate. • WWW.phy.mtn.edu/apod/astropix.html