## Astronomy: Black Holes

Answer each of the following questions thoroughly, clearly, and in detail, drawing your arguments and evidence from the resources we have used in this class. This is open notes/internet/textbook, but we expect that you will do your own work, and that you will not communicate or collaborate in any way with other students on this. All your responses must be in your own words and represent your own individual work. If you do use information from outside resources we expect you to provide sufficient citation (links, authors, titles, etc.) that we can easily check those sources; the textbook and the lectures generally qualify as ‘common knowledge’ and do not need to be cited.

Do not copy the questions themselves into your responses, as it tends to tag your submission as plagiarized.

1. (5 points) Suppose you were in a spaceship orbiting at a close but safe! distance from a black hole, and as an experiment, you threw a large clock from your spaceship towards the event horizon of the black hole. Assuming that the clock is large enough and your spaceships telescopes are powerful enough you would be able to watch the clock fall into the black hole by observing light coming from the clock, until the moment it passes beyond the event horizon and on towards the singularity at the black holes center.

In a few paragraphs, describe thoroughly and in detail the physical changes to the clocks appearance and behavior that you would expect to observe from your spaceship as the clock approaches the event horizon.

2. (5 points) Consider the following three different black holes, each with a different mass:

a) a stellar-mass black hole, with a mass 10 times that of the Sun;

b) an intermediate-mass black hole, with a mass 50 times that of the Sun; and

c) a super-massive black hole, with a mass 3.5 billion times that of the Sun.

For each of these black holes, use the scaling relationship given in class to roughly estimate the radius of their event horizon (in kilometers), and also describe briefly (in a few sentences each) the most common sorts of observational evidence the types of data we examine that reveal the presence of black holes with masses of those values.