Sure, everybody has seen Armageddon and knows that if an asteroid should come hurdling toward us, we'd just have to send up a bunch of dudes to stuff a bomb inside it. Easy!
But it turns out there are a whole lot of other, less well-known threats out there in the cosmos that that could wipe us out at any moment. And we'd probably never see them coming.
Stellar black holes are so-named because they are only "sort of" more massive than our sun, in contrast with supermassive black holes that can stomp an entire galaxy into oblivion because they feel like it.
There are thousands of these stellar black holes floating around space. The problem is, we have no way of finding them unless they interact with another stellar object and we happen to see it. One way they interact is by completely annihilating the object (in fact, that is their preferred method--they're kind of dicks about it).
Actual science picture.
In other words, a black hole could be right next to our solar system and we wouldn't know it until it starts snacking on the sun.
What You'll See
The sun will suddenly start unwinding itself, and then everything will go black. Soon after the black hole will begin the process of collapsing all matter into a single point. So you, your mom, your couch, your porn, the Pacific Ocean and a billion Chinese people will all be crushed into an area the size of a golf ball.
It'll look like this, only less photoshopped.
The good news is that you won't live to see that. The first thing that happens to you after you get sucked into space is that you get "spaghettified." That's the actual term used by scientists, and we'll let you use your imagination as to what it means. Hint: it has nothing to do with the black hole feeding you lots of delicious spaghetti.
Gamma-ray bursts are intense blasts of radiation that go rocketing into space when a star explodes, traveling at 99.99% the speed of light. We see these all the time, and they can even be spotted in different galaxies.
Why? Because they're really freaking bright. They are to our sun what our sun is to a Zippo lighter. And if a massive enough star explodes in our galaxy, its "wad" could hit us square in the chin.
There would be little warning, and one could be barreling down on us right now.
What You'll See
If you're on the side of the planet where it hits, this will be like getting caught in a nuclear blast 100 times stronger than all the nuclear warheads on Earth combined. You'll probably get through "OH" and half of "FUUUUCK" before you're interrupted by the sounds of your organs boiling.
If you happen to be on the other side of the planet, you'll simply burn to death from radiation as the atmosphere disintegrates and all the gamma-rays liquefy your cells. Some frequently asked questions during a gamma burst might be, "Why is the toilet water boiling?" "Why's mom all melty?" and of course, "Ouch, ouch, Oh dear God why?"
If we're lucky, it'll just be a "nearby" gamma-ray burst, which means it just grazes us. Oh it will still kill you, but the resulting death will be slower as the ozone layer burns up and our ecosystem is destroyed. So all those people you've always wanted to tell to fuck off? You'll have time to do it while the planet turns to Thunderdome around you.
There is a "Gamma-Ray Burst Coordinates Network," which attempts to detect bursts ahead of time, thus ensuring that we'll have time to run around in circles a few times while screaming our heads off before it hits.
Did you know that the sun (or the Deathball as it shall be called henceforth) is slowly expanding into a red giant. This won't happen for a long time (let those bitches in the year 5,000,000,000 deal with it) but it is getting hotter and closer as we speak.
And, due to the constant and massive nuclear reactions going on inside the Deathball, it turns out it's possible for it to suddenly expand a whole crapload at any time.
This won't help you at all.
What You'll See
Solar Expansion wouldn't kill you instantly. You'd have some time to go, "Say, did someone leave every oven in the state on and open for a few hours?" or, if you live in Riyadh, "That's it, I'm putting on a tank top and a pair of fucking shorts."
However, the situation would rapidly degenerate as all the water on Earth dries up in a couple of days. If you happen to live near a Costco and don't mind killing a few people for bottled water, you might last the week. Otherwise, you're probably screwed.