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AST201H1 Lecture Notes - Lecture 22: Elliptical Galaxy, Disc Galaxy, Cosmic Distance Ladder

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School
UTSG
Department
Astronomy & Astrophysics
Course
AST201H1
Professor
Bryan Gaensler, C. Barth Netterfield, Ilana MacDonald

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AST201H1 Lecture Notes - Lecture 20: Semi-Major And Semi-Minor Axes, Orbital Period, Vera Rubin

22

AST201H1 Lecture Notes - Lecture 22: Elliptical Galaxy, Disc Galaxy, Cosmic Distance Ladder

23

AST201H1 Lecture Notes - Lecture 23: Main Sequence, Cosmic Distance Ladder, Edwin Hubble

Document Summary

Irregular galaxies are a result of a collision of two galaxies (mergers. ) When its finish its star bursts, it will probably another disk galaxy. But if there is no gas or dust left then it will create an elliptical galaxy. To understand how big galaxies are, we need to know how far away it is. Parallax how we measure the distance of stars. This method only works for stars a few thousand light years away. The current instrument that is measuring parallax can only measure the stars within the milky way (though it has done a great job till now. ) Luminosity tells us how bright something is intrinsically. Apparent brightness is how bright something looks to us. The small fraction of light received on earth determines the star"s apparent brightness. The closer a star is to earth, the higher the fraction of its light we receive. The amount of light we receive goes down as the square of the distance.

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Related Questions

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An extrasolar planet can be detected by observing the wobbleit produces 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 thesame characteristics as Jupiter. That is, mb = (1.0 x 10-3)ma andthe planet has an orbital radius of 8.0 x 1011 meters. Determinethe radius ra of the star's orbit about the system's CM.
(c) When viewed from Earth, the distant system appears towobble over a distance of 2ra . If astronomers are able to detectangular displacements ? of about 1 milliarcsec (1 arcsec = 1/3600of a degree), from what distance d (in light years) canthe star's wobble be detected (1 ly = 9.46 x 1015 m)?
(d) That star nearest to our Sun is about 4 ly away. Assumingstars are uniformly distributed throughout our region of the MilkyWay Galaxy, about how many stars can this technique be applied toin the 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 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?