Hi all,

I am a PhD student focusing in cosmology. I wanted to up the science content here on Tildes, and I thought that one way to do so is to have an informal little Q&A session. As such, feel free to use this post to ask any questions you might have about cosmology specifically, and physics in general.

This may not be as exciting as some other science AMAs given that I am a rather early graduate student, so there may be a lot of questions I don't know the answer to. However, I'm willing to try my best and answer over the next few days, and to let you know I don't know if I don't!

A bit about myself: I did my undergraduate degree at the University of Chicago where I studied physics and mathematics, and then I was a student researcher in a computational cosmology group at a national lab. I subsequently enrolled at UC Davis to continue studying cosmology. Ask me anything about physics, cosmology, or high performance computing!

I also invite anyone else with expertise to chime in as well!

I do some astrophotography for fun in my spare time. I'd like to get into doing deep sky photography. In order to do that, I need a moving mount that can keep the camera aligned with the stars for minutes to hours at a time. I'll be using (at least initially) a Canon 7D (original version) with Canon lenses rather than a telescope. I currently have a 200mm lens with 2x extender, which makes it 600mm equivalent on that body.

I'd like to know if others here have ever done this and what type of hardware they've used for the motor and mount? Prices seem to be all over the place and options vary greatly on different devices. For example, I see the following:

Sky-watcher EQM-35 - $623.00US - Seems pretty full-featured for the price, as it includes tripod, motorized mount, alignment scope, and database of astronomical objects.
Celestron Advanced VX Computerized Mount - $899.00US - Seems very similar to the above, but does not include a scope, but is ~$250 more
Orion AstroView EQ Mount & EQ-3M Motor Drive Kit - $269.99US - Like the first one, but without the scope and holds less weight, and no database of objects to look at

I get the difference in price between the first and last, but not the middle one.

In any event, curious if anyone has used any of the above or any others and what their thoughts are on the quality of different brands, and anything I should be looking for or avoiding.

It is my understanding that if you are looking at an object falling into a black hole from a remote viewpoint, then the object will appear to take “forever” to complete the fall into the black hole. The object is effectively frozen in time at the black hole’s event horizon, from the remote viewer’s POV.

Is this the correct interpretation so far? If so, let’s remember that.

It is also my understanding that a black hole can increase in mass as it captures new objects. The mass does increase from an external viewpoint. Is this accurate?

If I understand known science on the above points, then the paradox I see here is that while the visual information is frozen in time from the external POV, the mass of the black hole does increase from the external POV. So is this where the Holographic Principle comes in? Or is there another explanation here, or am I off-base entirely?

Or is it just that the accretion disk gains mass and black holes never increase in mass from an external POV, after they are initially formed?

Is this known?

Please either attempt to answer my tortured question, or point me to material that might lead me ask a better question.

Thanks!