# PCS 181 Lecture Notes - Lecture 11: Giant Star

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21 Mar 2013
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Searching for a Black Hole:
They emit NO light, so we can’t see a Black Hole directly.
We seek a Stellar Black Hole in a binary system consisting of a visible Giant star and an
invisible and an invisible companion. (=BH Candidate).
The Search:
We seek a Giant Star that “wobbles” in its orbit.
The Companion causing the “wobble” must be invisible.
The invisible Companion must have a mass >~3Mo.
The system must be emitting x-rays (from a surrounding Accretion Disk).
Cygnus X I:
Best Stellar Black Hole Candidate.
We can see a visible supergiant star of ~30Mo.
The Supergiant Star is “wobbling” under the influence of an invisible Companion.
The System is emitting x-rays.
Mass of the invisible companion is ~9.5Mo.
Recall that a Black Hole singularity has a mass >~3Mo.
Review Problems:
Accretion Disk Problem:
A Black Hole Accretion Disk has a luminosity of 1030 W and emits x-rays of wavelength
1nm. Determine its temperature (in K) and its radius (in km).
T = 0.0029 m.k
T = 0.0029 m.k
1 x 10-9 m
T = 2.9 x 106 k
L = 4 (3.14) R2 (SIGMA) T4
R= [L]1/2
[4 (3.14) (SIGMA) T4]
[4 (3.14) (5.67 x 10-8) (2.9 x 106)4]
RAD = 1.41 x 105 m
OR
RAD = 1.41 x 105 m
1000
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## Document Summary

They emit no light, so we can"t see a black hole directly. We seek a stellar black hole in a binary system consisting of a visible giant star and an invisible and an invisible companion. (=bh candidate). We seek a giant star that wobbles in its orbit. The companion causing the wobble must be invisible. The invisible companion must have a mass >~3mo. The system must be emitting x-rays (from a surrounding accretion disk). We can see a visible supergiant star of ~30mo. The supergiant star is wobbling under the influence of an invisible companion. Mass of the invisible companion is ~9. 5mo. Recall that a black hole singularity has a mass >~3mo. A black hole accretion disk has a luminosity of 1030 w and emits x-rays of wavelength. Determine its temperature (in k) and its radius (in km). L = 4 (3. 14) r2 (sigma) t4.

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