Space, it turns out, is large. And until we humans figure out how to move faster than almost standing still, we won’t be going anywhere interesting in it any time soon. So we can count out exploring the cosmos on foot for the time being. But what we can do is observe. We do that a lot, actually, and even though the percentage of the universe that has yet to be meaningfully explored is just about 100%, we do at least know that it’s filled with awesome and unspeakable wonders, breathtaking majesty, incomprehensible vastness, and lots and lots of really big things that want you dead. Here’s a few of those…
Stars are more or less defined by the tug of war that exists between the explosive, outward push of nuclear fusion, and the inward pull of their own gravity. Eventually, though, they all run out of fuel to hold that gravity at bay and collapse under their own weight. What form of stellar corpse the star’s core takes at this point depends on its mass. The vast majority of stars, including our sun, simply don’t have enough of that mass to end up as anything other than a simple white dwarf. For more massive stars, though, so much gravity will be crashing inwards at the end of its life, and with such immense energy, that the negatively charged electrons of its constituent molecules will be smashed directly onto the positively charged protons of its own nucleus, canceling out the charges and leaving behind a neutrally charged ball of, well, neutrons.
The resulting neutron star is so dense that a teaspoon of it in earth’s gravity would weigh as much as a mountain, and the whole former star’s mass (keep in mind, we’re talking about a star 10 to 29 times as massive as the sun) would be squeezed into a sphere no larger than say, Philadelphia. Think about that: multiple sun’s worth of mass (and gravity), all vacuum packed into a sphere you could, at least on paper, drive across in a matter of hours. Also worth noting: gravity is, by several orders of magnitude, the weakest of the four known fundamental forces of physics. So asking how much of it you’d need to overwhelm the nuclear forces in this way is like asking how many sheets of paper you’d have to stack on the deck of an aircraft carrier to sink the ship. Answer: a lot.
If you’re ever gazing out at the night sky and spot a star that appears to be blinking, it’s not. At least, not really. What you’ve probably got is a pulsar: a unique type of neutron star characterized by immensely powerful beams of highly concentrated electromagnetic radiation rocketing out of its magnetic poles as the star spins rapidly beneath them.
That spinning, and the fact that the beam is only visible when facing you directly, is what it accounts for the blinking illusion. It’s kind of like a lighthouse in that way (except in this case, you should never, ever follow the light). Turns out, pulsars are very useful to astronomers, too. The first extrasolar planets were found orbiting one, and the incredibly regular period of their rotation makes them wonderful time keeping devices, with some of them even rivaling atomic clocks. So that’s cute. You know. From way, way over here.
In case you haven’t picked up on it yet, please do not visit neutron stars. Especially not magnetars, defined by the breathtakingly powerful magnetic fields they possess. To put into perspective how mighty those fields are, consider this: Earth’s magnetic field clocks in at 1 gauss (it’s how we measure gauss). The sun? Surprisingly not too much more intense, capping out at around 100 gauss. An MRI has 10,000, and the strongest human-made magnetic fields typically do not exceed a million gauss, since we don’t yet have instruments sophisticated enough to withstand levels of intensity beyond that. Neutron stars? Not a million. Not a billion, even. Try 1 trillion-gauss. That is, to put it mildly, quite impossible to adequately describe.
Magnetars are even nuttier, with magnetic fields in excess of 1 quadrillion gauss, compared to earth’s 1. That’s enough magnetic intensity to utterly atomize you if you were to get within several hundred miles of this thing (keep in mind, the thing itself is very small). And it doesn’t stop there. When those magnetic fields decay, all sorts of deadly radiation is thrown out into the cosmos, from x-rays to wickedly deadly bursts of gamma radiation. In case you’re wondering, no, gamma ray bursts won’t turn you into the Incredible Hulk so much as they’ll turn your entire planet into a scorched hellscape. And here’s the killer: neutron stars of any type are only the second craziest thing stars can end up as after they die. For stars even more massive than the ones that become these, the force of their end-of-life gravitational collapse is so immense that it blasts right past the Chandrasekhar Limit holding up white dwarfs, past even the Tolman-Oppenheimer-Volkoff Limit of degeneracy pressure for sustainable neutron stars, and all the way down to…
…we don’t know, exactly. And anyone who tells you they truly understand where the gravitational collapse of supermassive stars ends, or what exists in the center of the resulting black hole, is lying to you. If you plug the numbers into the existing equations, you’ll get ‘infinity’ as an answer. Lots of people take that and run with it, yelling far and wide that the gravitational collapse of sufficiently massive stars is so powerful that they result in an infinitely small, infinitely dense object with infinite gravity known as a gravitational singularity. Problem is, while ‘infinity’ is a fine mathematical answer, it’s a woefully inadequate one when you’re trying to describe actual physical phenomena (after all, saying something is ‘infinitely small’ is the same as saying ‘this object doesn’t exist’). So what it’s really saying with that answer is, ‘your math is wrong.’
And it is: our current equations are simply not sophisticated enough to describe what’s truly at the center of something as extreme, dangerous, and powerful as a black hole. And it’s not like we can just go snap a picture of its interior, either, because they are, by definition, invisible. If you had a death wish you could certainly venture past the event horizon (the point of no return, beyond which not even light can escape), but that still wouldn’t be good enough. Because even if you somehow avoided being stretched into a string of individual atoms (or, as scientists literally call it, ‘spaghettified’) long enough to plant your eyeball on whatever the actual black hole’s center is (please do not do this), you still wouldn’t be able to see a thing because all light is rushing towards this object, and none away from it.
So until we can figure out how to unify General Relativity (big picture physics, dealing with stars, gravity, and supermassive objects, among many other things) and Quantum Physics (small picture, atomic and subatomic scale things like what a black hole’s center likely is), we will never get to the bottom of this. Hopefully someone will one day, and maybe it’ll even be you! But don’t hold your breath: the inability to unite our two grandest theories has stumped physicists for decades, leading us down some mathematically gorgeous but ultimately untestable mathematical rabbit holes like M or String Theory (which requires the existence of 11 dimensions in order to make the two theories play nice with each other). Even Einstein himself, the man who unified space and time, and matter and energy, died trying and failing to unify his own Relativity (which led to the discovery of black holes to begin with) and the simultaneously emerging conclusions of Quantum physics. So… good luck with all that. In the meantime, though, stay away from black holes.
Supermassive Black Holes
There’s an argument to be made for just throwing this in with the last section, but supermassive black holes are so much more dangerous, fascinating and, well, massive, than standard stellar ones (which are hardly boring themselves) that they deserve their own mention. Now, scientists are fully aware that supermassive black holes, which can have masses millions or literally billions of times that of the sun, could not possibly have been formed from a single stellar collapse. The verdict is still out on how they came into existence, but it’s likely the things have had enough time to devour lots of tasty stars, nebulae and everything else in their path, and merge with other black holes.
Additionally, every galaxy has a supermassive black hole in its center (the Milky Way’s is Sagittarius A*), which puts it in the immediate vicinity of what can only be described as a cosmic buffet. Give it enough time in such an environment, and you’ll likely have a supermassive black hole at some point. Interesting side note: death would actually come more slowly for you if you were unfortunate enough to tumble into one of these behemoths, as opposed to their smaller cousins. That’s because they’re so incomprehensibly vast that it could be hours, days, or possibly longer after passing the event horizon before you realized anything was amiss at all. There’s still no escaping, unfortunately, and it’ll still hurt like hell when the time comes, but hey! You’ll at least have a little extra time to gawk in awe at the spectacular way in which you’re about to be ripped down to your individual quarks. Have fun!
It’s difficult to find words in any language that can adequately describe the luminosity, mass, and awesome power wielded by quasars. To get an idea of what a quasar is, imagine a supermassive black hole from the last entry, but with a titanic, astrophysical jet of superheated gas rocketing into the cosmos from both ends (not unlike a pulsar, but immensely bigger), generally perpendicular to the gaseous accretion plane that feeds it.
These ancient behemoths can quite easily outshine their host galaxies, and the most luminous ones can do so many thousands of times over. If you’re worried about death by quasar, though, don’t be. The nearest one, 730 million lightyears away, is merely a whisper of a long-dead beast. The closest active one (at least, visibly active, although it’s likely long dead by now) is 3C 273, a right-around-the-corner 1.7 billion lightyears away. But let’s keep it that way please, and hope that a well earned spot at the top of our list will be enough to appease them.