Why do some stars turn into black holes?
Stars that were massive enough turn into black holes when they die.
A dead star doesn't have enough fuel to keep fusion going.
The fusion reaction produces energy and heat that counterbalances the gravitational pull of the star on itself
This is called "hydrostatic equilibrium"
Objects in a system orbit around the center of mass
Galaxies in a cluster kind of orbit each other rather than expanding and spreading out the way the Hubble pattern would predict. SO they become more inclined to collide.
What keeps smaller object in orbit, rather than falling towards the central mass?
* the energy of the small object itself
* orbit is at a point where energy of object balances the energy of gravitational pull
gravitational tides between galaxies can affect orbits if the galaxies are close enough
During a galactic collision, you're likely to have more material falling into a black hole
Time travel very speculative - all of the discussion is theoretical at this point. Some ways time travel might happen:
*Faster-than-light (back in time)
*Travel through wormhole w/o getting destroyed
* Go to similar parallel universe
* Are parallel universes preexisting, or created by the act of time travel
* If parallel universes exist, there would probably be an infinite amount of them, for each branching-off point. If there was a limited amount,how would it be chosen?
* Parallel universmany not just have different history, but different laws of physics
Standard candle - a group of objects with the same brightness.
Different form units of measure such as "solar luminosity"
Standard rod -similar concept with shape
In astronomy, can measure apparent brightness and apparent size.
apparent brightness, apparent size, actual size, actual brightness and distance - if you knoow some fo these, you can figure out the rest
"Do black holes ever go away?"
The massive ones are around forever,the smaller ones are likely to disappear
The Drake Equation - equation that takes several factors; determines the probability of intelligent life; however, you have to make assumptions
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