Homework 09 Solution
Please answer at least 4 of the following 5 questions correctly for full
credit:
Question 1
Which two quantities do we try to estimate in our effort to identify Black
Hole candidates?
Answer
We are looking for a huge mass (at least ~10 solar masses) in a small space.
So the two quantities we need to estimate is mass (from orbital motion) and
size (e.g. from the duration of spikes in radiation signals or the smallest
orbits observed).
Question 2
Which constant of nature relates the time duration of spikes in emitted
radiation to the size of the emitting object or region?
Answer
The speed of light (in vacuum...).
Question 3
What is the numerical value of the escape velocity at the Event Horizon as
measured in kilometers per second? (Value rounded to within 1 percent is okay.)
Answer
The escape velocity at the event horizon is the speed of light (in vacuum...).
Its numerical value is 300,000 km/sec (precisely: 299,792,458 m/s...).
Question 4
Which class of variable stars has a luminosity that is almost independent of
the period of an individual star's variability?
Answer
The RR-Lyrae stars. See lecture 30 page 10. Cepheids have a linear dependence
of luminosity on period.
Question 5
How are the Globular Clusters that are associated with the Milky Way galaxy
distributed around the Galactic Center?
Answer
They are moving in a spherical halo to the galactic disk. Their motion in
that halo is not locked to the rotation of the galactic disk: their orbits
around the galactic center are randomly oriented.
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Last modified: Fri Apr 11 10:27:37 MDT 2008