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.
This phenomenon is just what it sounds like: When two galaxies run into each other, one eats the other. Planets go crashing into each other and get sucked into supermassive black holes, and solar systems get "ejected" from each galaxy. The term "clusterfuck" was invented to literally describe what happens in these cases.
This, on the other hand, is Galactus Cannibalism.
Now, the closest known galaxy that will probably run into ours is the Andromeda Galaxy, which is sauntering toward the Milky Way at a lazy 120 km/sec. In case you just ran into the other room screaming, "SHIT! PACK OUR SHIT!" get back in here and relax. At that speed, they won't run into us for about 3 billion years.
However, there are galaxies out there we can't see. They are called dark galaxies (or "ninja galaxies" for the purpose of this article) and they are made up solely of dark matter and black holes. One of these silent killers could run into us any ol' time now.
What You'll See
We've never observed this happening before, but scientists have theorized that it'll be about the most spectacular and flashy goddamned thing ever.
Like this, but you'll be dead.
Planets will go hurdling through space, supermassive black holes will eat solar systems and shit out Quasars. It'll be a billion Michael Bay movies playing out across the heavens at once.
There is a mysterious force operating in the universe called "dark energy." If that sounds scary, it's because astrophysicists like to come up with scary names for things that are actually code for "We have no idea what this is."
So, aside from being the next name for your death metal band (as soon as you find a drummer), dark energy currently spends its time hurdling everything in the universe away from itself, like everyone did that time you pooped in the pool.
More importantly, scientists say dark energy may be responsible for the Big Bang and creating the universe. And they say it might not be done. Dark energy may, at any moment, decide play out the Ghostbusters "cross the streams" scenario and randomly split every atom in the universe.
What You'll See
An astrophysicist calmly stated, "It's like turning off all the lights... it's the end of time, the end of the universe."
While you're trying to wrap your head around that, just remember that if it happens, you won't care. You won't care because you won't exist. It could happen before you finish your next sentence.
Why aren't they doing something about this, dammit? It's time to send out a ship, find the Dark Energy, and blow the shit up.
In case life-ending threats from the far reaches of space didn't make you shit yourself, have a look at the ones here on Earth that'll do the trick just as well in 5 Bizarre Ways the Weather Can Kill You Without Warning. When you're through with that, learn how to deal with your grief in 7 Methods for Coping with Tragedy (Courtesy of James Bond).