So how can one model a Black Hole? Some suggested to me the book "The Krone Experiment" a few months back. I finally fetched it for my Kindle (there is also a DVD). I just started it yesterday and find the concept interesting. A Russian Carrier is damaged by what the Russians believe is an American space based weapon. This brings them to near war. Several other events happen and a CIA guy and a computer sim gal start to piece it together. With the help of a small think tank of scientists, they think a Black Hole is captured by Earth, orbiting with a perigee of ~10,000 miles. We're talking 10 million metric tons the size of a nucleus. I'll finish the book tomorrow.
So, I could not figure out how to model this thing in AstroGrav. I sent a note to Russ Calvert (author of AG). He created a sim and sent me some detailed directions on how to do my own. If you want the sim he crafted, let me know so I can send it to drop box.
His reply.........and instructions
Hi Kenneth,
This is an interesting problem!
The short answer is that you can’t model this with AstroGrav. The reason is that once the particle is inside the Earth, the Earth’s gravitational attraction is pulling the particle in all different directions instead of just towards the centre, so that all the normal ideas of elliptical orbits, fixed orbital periods, etc, break down. I’ve no idea what the correct physics is to cover such a situation, but I imagine that somebody somewhere has studied it and published papers about it.
However, you can model a particle orbiting within the Earth, but the physics won’t be correct. Try the following:
(1) Open the ‘Planets, Moon’ sample simulation.
(2) Close the ‘Structure’ and ‘View From New York’ windows, as they just get in the way.
(3) Select the ‘Edit / Add Object…’ command and choose the Earth as the parent. You should then see a ‘Editor of ‘Earth/2’’ dialog.
(4) Edit the ‘Type’ to ‘Asteroid: Small’ (it will do), and OK the window asking about updating various other fields.
(5) Change the ‘Semi-Major’ to 3186km, which is slightly more the half the Earth’s radius.
(6) Change the ‘Eccentricity’ to 0.999.
(7) Leave the other fields as they are for now, and OK the dialog.
(8) You should now have added your particle orbiting (mostly) within the Earth. If you check its orbital period in the table, you should see a figure of about 0.02 days, which is about half and hour, so use the ‘Evolve / Settings…’ command to change the time step to 1 minute, which should be just about ideal to see what’s going on.
(9) In the ‘View’ window, zoom in on the Earth using Ctrl+drag, fixing on the Earth, and reducing the brightness until you have a nice big Earth filling up most of the window. You might want to make the window much bigger too.
(10) Use the ‘Edit / Find…’ command to find and select the particle. [You can’t select the particle simply by clicking on it, because it’s inside the Earth, and you’ll select the Earth itself!]
(11) Start the simulation running. You might or might not see the particle popping out of the Earth at apogee depending on exactly how you’ve got the Earth oriented.
(12) Choose the ‘View / Show All / Objects’ command to hide the objects and effectively make the Earth transparent. You should now able to see the particle orbiting.
(13) Use the ‘Ctrl+Alt+Shift+G’ and ‘Ctrl+Alt+Shift+L’ commands to display the Earth’s coordinate grid and the locations that you see with the ‘Tools / Edit Locations…’ command. [Two Easter eggs that you might not already know about.]
(14) Play around rotating the Earth and editing the particle’s orbital parameters as you want.
Here’s my version: