Is Thor (MCU) a god or not? It's implied he isn't in 'Thor: The Dark World', but he's constantly referred to as 'God of Thunder'.

It depends a little bit God by a monotheistic perspective? No. But god in a mythological sense? Maybe? not quite but closer. Odin explicitly calls Loki out on his god complex in Dark world and dark world plays the cinematic Thor as almost straight sci fi.

The first Thor movie balances it saying the Asgardians consider science and Magic the same. Most people just run with this saying that means its all just super advanced scifi. But the movie Shows the Asgardians as considering Loki a sorcerer and some of the deleted scenes showed his abilities being a bit more advanced then they were portrayed later. And over all Odins abilities and the worthiness enchantment fall far more into the realm of magic than science fiction. And the Asgardians were of course the basis of the marvel universes version of Norse mythology and worshiped.

Thor Ragnarok playes it a bit closer to the first Thor the Dark World at least in the matter of power of the the royal family and Infinity War has Heimdall say "Allfathers, let the dark magic flow through me one last time..."
So I think its safe to consider the marvel cinematic version of the Aesir a Magitek using heavy race of highly powerful and mystically empowered (at least the royal family and some court members) beings. And they do seem to take to the godly titles.

So literally gods? No.
But with all that I wonder how much more it take to be considered gods by ancient standards?

Not actual Gods, just powerful creatures that humans mistake for gods.

The Asgardians admit themselves that they are not gods. They just happen to be different species. They don't seem to be immortal, either; Odin showed some very clear signs of aging and was clearly not in his prime anymore, suggesting that there is a prime to be in.

God of ______ is just a title that the Asgardians like to use. In their age and superiority over the other 9 realms, they grew arrogant.

If aliens visited Earth today and were several thousand years more technologically-advanced, what in God's name would we do?

No civilization, no matter how technologically advanced can ever prevail and continue its existence if it lacks civility and respect for the nature in which it exists. Infact both technological and civil progress are interdependent. By civil progress I mean sustainable development, balanced development and controlled growth keeping in view the

If light does not have mass, then how can it be absorbed by a black hole?

Lots of great answers here and they all seem correct.  I'll just reemphasize a few bullet points.1.) The notion of force is a very tricky concept in relativistic settings and is usually avoided altogether since it ends up being more trouble than it's worth.  Massless particles are the ultimate relativistic setting.   2.) General Relativity

What are astrobiologists currently studying? What do astrobiologists expect the first kind of extraterrestrial life to be like?

find out for yourself -Astrobiology WebAstrobiology Magazine Exploring the Solar System and beyondMary Ann Liebert, Inc., publishersYou can even get a degree in it.