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Stellar Mass

Stellar Mass. Determining the Mass of Stars. It is difficult to determine the mass of stars. Astronomers use the gravitational field produced by a star to determine its mass... Heavier stars have a greater gravitational field.

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Stellar Mass

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  1. Stellar Mass

  2. Determining the Mass of Stars • It is difficult to determine the mass of stars. • Astronomers use the gravitational field produced by a star to determine its mass... Heavier stars have a greater gravitational field. • Astronomers study how objects, like another star, behave as they pass through the gravitational field.

  3. Binary Stars • Binary stars are pairs of stars that orbit each other. • The gravitational attraction between two stars pulls them toward each other. • They rotate around a fixed point between them called the center of mass… think about a seesaw.

  4. Center of Mass • If the stars are the same mass, the center of mass will be exactly in the middle. • If they are different masses, the center of mass will be closer to the heavier star.

  5. Mass Ratio • Ratio of Masses • The heavier star has a smaller orbit because it is closer to the COM. • MA / MB = rB / rA • This approach only tells you how much larger one is than the other.

  6. Mass, Orbital Distance, & Period • Recall Newton’s Universal Law of Gravitation & Kepler’s 3rd Law… • MA + MB = r3 / T2 • R is measured in AU and is the distance • T is measure in years and is the time for one orbit (Period)

  7. Solar Masses • The majority of the mass in our solar system is the Sun so the total mass is thought of as 1 solar mass. • In other systems, the solar mass is not always 1.

  8. Example • A binary system has a period of 32 years and an average separation of 16 AU. What is the total mass? • 163 / 322 = 4 solar masses • Suppose Star A is 12 AU from the COM and B is 4 AU away. Find the individual masses. • MA / MB = 12:4 or 3:1 • The masses must add up to 4 and have a ratio of 3:1… • Star B = 3 • Star A = 1 (larger period)

  9. Not Always So Easy… • Many binary stars orbit each other in an elliptical pattern. • Many orbits are also tipped at an unknown angle. • The distance to the stars must be known so the size of the orbits can be estimated.

  10. Types of Binary Star Systems • Visual • Spectroscopic • Eclipsing

  11. Visual Binary System • Both stars are separately visible through a telescope • That means the size of the orbit must be large • Nice Diagram on pg. 202 • Other Images http://www.google.com/search?q=visual+binary+star+system&hl=en&prmd=imvns&source=lnms&tbm=isch&ei=kgYrT_r0IImw2QXKt9niDg&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CAwQ_AUoAQ&biw=1280&bih=595

  12. Spectroscopic Binary System • The two stars appear to be a single point of light through a telescope. • Spectral analysis shows red shift and blue shift as the stars orbit each other. • Nice Diagram on pg. 203

  13. Eclipsing Binary Systems • The two stars cannot be distinguished when looking through a telescope. • Astronomers analyze a light curve and see a difference in brightness over time. • This shows that the two stars are passing in front of each other and block some of the light. • Nice Diagram on pg. 205 • http://www.google.com/search?q=visual+binary+star+system&hl=en&prmd=imvns&source=lnms&tbm=isch&ei=kgYrT_r0IImw2QXKt9niDg&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CAwQ_AUoAQ&biw=1280&bih=595#hl=en&tbm=isch&sa=1&q=eclipsing+binary+system&oq=eclipsing+binary+system&aq=0S&aqi=g-S2g-mS1&aql=&gs_sm=c&gs_upl=9328l11172l0l14672l9l9l0l0l0l0l63l561l9l9l0&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=fa3fe87ccfc37441&biw=1280&bih=595

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