Ask An Astronomer Anything At All About Astronomy (VIII)

Yeah, I know, these don't come out weekly, but better ever than never. As always, find the full set of questions on the Q&A page.

1) Will the Milky Way and Andromeda really collide in the future ?
Probably.

2) How can there be hot gas in space if space is so cold ?
It's very thin.

3) Could we have stopped asteroid 2015TB145  with just three weeks warning ?
No.

4) Wouldn't asteroid 2015TB145 have just broken up in the atmosphere with no harm done ?
No.

5) Why are dwarf galaxies worth studying ?
Because they're really cute.

6) Could dark matter just be normal matter that exists in another universe that only interacts with ours through gravity ?
No.

7) Why is radar used for hunting asteroids ?
It isn't.