AST251H1 Lecture 11: AST 251 Lecture 11

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magentaduck547

2 May 2012

School

UTSG

Department

Astronomy & Astrophysics

Course

AST251H1

Professor

H.Pfeiffer

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Document Summary

Higher mass stars have a higher temperature and luminosity but a shorter lifetime. Planets around binary stars: a 3-body system stable only if two bodies close to each other, the third body much farther away. A planet may orbit a close binary system or one of the components of a wide binary system. Orbits of comparable size are unstable and the planet will be ejected. Finding an extra-solar planet will be difficult: distances. Distance to next star 4. 4 ly = 280 000 au. 2000x farther than any man-made craft has gone. Galaxies hold a lot of stars but there"s even more empty space between. When galaxies collide, on average, no two stars crash into each other because there is so much empty space between stars: size and mass. Radius of planet 1/10 1/1000 of radius of star. Light from planet will be a tiny fraction of star-light. Mass of planet 1/100 1/100 000 of mass of star.

Related Questions

Why do astronomers find it difficult to locate extrasolar planets with telescopes?

A. From our distance, they are very close to the stars they orbit.

B. Planets wobble due to the gravity of the stars they orbit.

C. Planets only emit invisible wavelengths of light.

silvermule348

An extrasolar planet can be detected by observing the wobble itproduces on the star around which it revolves. Suppose anextrasolar planet of mass mb revolves around its star of mass ma .If no external force acts on this simple two-object system, thenits CM is stationary. Assume ma and mb are in circular orbits withradii ra and rb about the system's CM.

(a) Show that ra =(mb/ma)rb

(b) Now consider a Sun-like star and a single planet with the samecharacteristics as Jupiter. That is, mb = (1.0 x 10^-3)ma and theplanet has an orbital radius of 8.0 x 10^11 meters. Determine theradius ra of the star's orbit about the system's CM.

(c) When viewed from Earth, the distant system appears to wobbleover a distance of 2ra . If astronomers are able to detect angulardisplacements ? of about 1 milliarcsec (1 arcsec = 1/3600 of adegree), from what distance d (in light years) can the star'swobble be detected (1 ly = 9.46 x 10^15 m)?

(d) That star nearest to our Sun is about 4 ly away. Assuming starsare uniformly distributed throughout our region of the Milky WayGalaxy, about how many stars can this technique be applied to inthe search for extrasolar planetary systems?

An extrasolar planet can be detected by observing the wobble itproduces on the star around which it revolves. Suppose anextrasolar planet of mass mb revolves around its star of mass ma .If no external force acts on this simple two-object system, thenits CM is stationary. Assume ma and mb are in circular orbits withradii ra and rb about the system's CM.

(a) Show that ra =(mb/ma)rb

(b) Now consider a Sun-like star and a single planet with the samecharacteristics as Jupiter. That is, mb = (1.0 x 10-3)ma and theplanet has an orbital radius of 8.0 x 1011 meters. Determine theradius ra of the star's orbit about the system's CM.

(c) When viewed from Earth, the distant system appears to wobbleover a distance of 2ra . If astronomers are able to detect angulardisplacements ? of about 1 milliarcsec (1 arcsec = 1/3600 of adegree), from what distance d (in light years) can the star'swobble be detected (1 ly = 9.46 x 1015 m)?

(d) That star nearest to our Sun is about 4 ly away. Assuming starsare uniformly distributed throughout our region of the Milky WayGalaxy, about how many stars can this technique be applied to inthe search for extrasolar planetary systems?

AST251H1 Lecture 11: AST 251 Lecture 11

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