This morning, I got up early to watch the Chinese satellite Tiangong 1 whiz by. (If you've been reading the news, Tiangong 1 is expected to burn up and crash to the Earth this weekend.)
And "whiz by", it did. It was "apparently" traveling 2-3 times faster than you'd see an airplane (or the International Space Station) fly over the night sky, which is to be expected because it's about 2¼ times lower in altitude than the ISS is right now, but traveling at approximately the same speed.
With the full moon, I didn't think I'd see it, nor capture it on my camera. But here it is: very little motion blur. Just a slightly long exposure with the ISO set to 800 (although in the photo I'm posting, I've jacked up the contrast a ton so you don't have to download the image to see it). In the center you'll see two "stars"; the one to the upper-left is actually Saturn and the one to the lower-right is Mars. Just to the left of Saturn, spaced approximately the same, is a much dimmer "star", and that is Tiangong 1, whizzing by in one of its last orbits ever.
[Teditor's Note: I originally wrote this for Facebook and included a bunch of pictures in it. Unfortunately, I own none of the rights to the pictures so I really don't feel comfortable posting them in a public blog. (Too bad, some of them were bad-ass!) So instead, I have to present a cut-and-dry account of black holes and hope that you, dear reader, make it to the end without needing caffeine pills. Good luck!]
In honor of Stephen Hawking’s death, I wanted to do a write-up on black holes because this is the primary area of research he’s known for. And while I think many people know a little bit about black holes, a) a lot of people get the details wrong, and b) they’re so much more amazing than you might realize. Black holes are one of those topics that sucks me in (no pun intended...I swear!) and illustrates first-hand how truth can sometimes be stranger than fiction.
No joke, though: This is going to be a loooong post. And without any pictures, if this stuff ain't interesting to you, you're probably not going to make it to the end. But if you maintain an open mind and can get fascinated that everything I'm talking about describes the universe we live in, then hopefully you'll get the same thrill from reading this as I did from writing it.
I’m going to be semi-scientific in the way that I write this. Meaning, for example, that I may say two things “weigh” the same, even though in space I should be talking about mass. But at the same time, I’m not going to dumb down a topic, either.
Also, in order to explain some things, I’m going to have to go into some back story first (although I think/hope they’ll be all interesting!). You know that expression, “If I have seen further it is by standing on the shoulders of Giants”? (Isaac Newton) A lot of giants have led us to where we are today in our understanding of these most exotic objects.
Black holes are not
Before we delve into what black holes are, it’s important to dispel some popular ideas first.
Black holes are not giant vacuums that suck up everything in existence. If you were to remove our sun and replace it with a black hole that weighed the same, nothing would happen. ...well, that’s not entirely true. We’d all freeze, but we wouldn’t all be sucked up into it; Earth and the rest of our solar system would continue to swirl around the black hole until the universe died. That’s because black holes operate on gravity; the same gravity that governs our sun, Earth, the solar system, and the apple that dropped on Newton’s head. There’s nothing exotic about the gravity on the outside of a black hole. There is exoticism about its size, though: While our current laws of physics don’t prohibit a black hole the mass of our sun; there is currently no known mechanism to produce one that weighed that little. But if we could find a black hole the mass of the sun, it would only be a couple of kilometers across (!!!!).
Black holes are not close by. Someone once asked me if there are any black holes in our solar system. Nope. Certainly not of any reasonable size...and again, there is no known method by which black holes get to be small (with one caveat*), but if there were, we would’ve detected it probably 200+ years ago because it would affect the orbit of our planets. Aside: In 1846, two astronomers used math to predict Neptune. If Pluto is not a planet, then Neptune is the only planet that can’t be seen with the naked eye; nobody thought it existed until the math -- based on the wobble of Uranus’s orbit -- predicted not only its existence, but where it should be in the sky. On September 23 of that year, a third astronomer pointed a telescope right where the math had predicted it would be, and there it was! With that said, if a black hole were floating out somewhere in the solar system, our ancestors would have known about it.* Caveat: There is a theoretical object, “micro” black holes. But they would’ve only existed in the early universe and disappeared nearly instantly after creation.
Black holes are not black. If you were to look at one with your own eyes, it might appear black. But, in fact, black holes are constantly radiating stuff out into space, even when they’re not “eating” anything. More on this later.
Black holes are not forever. More also on this later!
What are black holes and how do they form?
Most people know that a black hole is a region of space where so much gravity exists that not even light can escape it. (Wait a sec...a second ago, I said black holes radiate stuff...how is that possible if nothing can escape? Patience!) Consider that thought, for a moment. Black holes are the densest things in the universe. The second-densest thing is called a neutron star, so named because it's made of neutrons (scientists aren't always the creative type with names). Neutron stars can weigh up to 3x the weight of the sun while being a little wider than Manhattan is long.
You can imagine that anything that dense would have some intense gravity, and you’d be right. A common thing you hear is that a sugar cube’s worth of neutron star material would have the same weight as Mt. Everest. (Others have said it would be the mass equivalent of squeezing every human on Earth into a sugar cube. But I like the Everest comparison better because: a) The size of humanity changes over time, and yes, Everest does, too, but at a much slower rate. And b) That’s morbid.) If you were to try putting that sugar cube in your coffee, it would fall straight through the Earth and leave an enormous crater in its wake. But don’t worry about falling in, for you would have certainly died in the massive megaton bomb-equivalent energy release that would have followed.
You could definitely not walk on a neutron star: Assuming you tried to land on one, your atoms would be crushed into the surface at a third the speed of light, probably causing some nuclear fusion on the way. Ultimately, you might end up as a molecule-thick oil slick on the surface of said neutron star.
Now, just remember that a black hole is much worse than that!
What are stars and how do they form?
Before we further define black holes, it’s important to know how they form. As they form from star collapse, it’s important to know what stars actually are. So we need to go back to school a little bit.
The universe is filled with gas. What’s the simplest molecule out there? (Remember back to the upper-left corner of your periodic table.) It’s hydrogen! When the Big Bang occurred and the universe cooled, hydrogen gas (and some helium) condensed everywhere. In space, hydrogen coalesces because gravity attracts it together. As it coalesces, it gets more massive and therefore gravitationally stronger, thereby attracting more and more hydrogen. The more hydrogen in one space, the more the atoms get squeezed together. Wash, rinse, repeat.
You can put two hydrogen molecules together, but that doesn’t mean they’re going to join together and become one. Remember bar magnets? Like repels like: positive repels positive, negative repels negative. When you smoosh two stable molecules like hydrogen together, their negatively-charged electron clouds (remember: electrons are negative; protons are positive) repel each other. With enough pressure, though, the molecules can slip past each other’s electron clouds. And if the nuclei get close enough to each other, the strong nuclear force takes over and attracts protons and neutrons to protons and neutrons, creating a new atom or molecule (recall from your science classes that the number of protons in an atom determines what that element is). Put enough pressure on hydrogen, and it fuses into helium. When that happens, the molecule reaches a lower-energy state and ejects 0.7% of its mass as energy according to a little-known equation from Einstein, E = mc². “c” is the speed of light, which is a big number. Squaring it makes it immensely bigger. Multiply m (that 0.7% of mass lost) by c² and you have a huge amount of energy. Imagine this energy release happening all over the place, and a star is born.
[Note: I’ve oversimplified this process. In reality, hydrogen fusion actually happens in three steps, and because I'm not a physicist, I haven't memorized those three steps, nor do I care to, anytime soon. It doesn’t matter for this, though. The point is, hydrogen collapses under its own gravity, fuses, and releases energy. Boom! Literally.]
Aside: Nuclear fusion is the holy grail of energy production, today. Every nuclear reactor you know of (in 2018 when this was written) is a fission reactor, which relies on the radioactive decay of certain elements to heat water to create steam to run turbines. It's a completely different technology than nuclear fusion. Why is nuclear fusion so amazing? E = mc². A little tiny mass creates a whole lot of energy. No more massive freight trains filled with coal going into the power plants, no more massive freight trains taking radioactive waste out to Nevada for underground storage.
That’s not the whole picture, though. When hydrogen crushes together and nuclear fusion ignites, the released energy creates an outward force. So now you’ve got gravity trying to crush everything inward, and you have the “E” from all that E = mc² fusion pushing its way out of the star. Eventually, the two of these find some balance and the star remains a certain size for billions of years until the star starts to run out of fuel.
Star death = black holes (sometimes)
A star runs out of fuel because it's busy fusing of its fuel into something else. So stars start out as mostly hydrogen and spend most of their lives fusing hydrogen into helium. After a while, when there's little hydrogen left to push the star outward, the core of the star collapses. In this collapse, it's now hot enough that helium starts pushing together, and it fuses into carbon. This does not go on forever: A star the size of the sun can't go any further than carbon because it simply doesn't weigh enough for another core collapse to crush carbon to cause fusion.
You may already know this, but our sun will not produce a black hole when it dies. It also won't produce a supernova, either: That's because the fusion cycle stops with carbon. (Our sun will one day turn into a white dwarf, but that's a story for another day.) But, heavier stars (meaning, about 8x the mass of our sun) keep going, and carbon fuses into neon, magnesium, and sodium. Eventually, it gets hot enough that neon fuses into oxygen and more magnesium. Hotter still, and in stars 10x greater than our sun, the oxygen fuses into sulfur and silicon. Even hotter still, and silicon fuses into eight different elements, one of which is iron.
Iron is a whole other beast, but before I get to that, I want to point out that each one of these cycles takes a drastically shorter amount of time than the cycle before it. Recall that I said earlier that a star spends most of its life (millions to billions of years) turning hydrogen into helium. Oxygen fusion lasts only months, and when the core collapses, it sends a shockwave that takes about a day to pass through the star, and when it does, it actually speeds up the silicon fusing. Silicon fusion lasts one day, and no matter how big the star, that silicon-burning day is the last day of that star's life.
Silicon fusion produces iron, and iron is no bueno for stars. Once iron starts getting made, the star has seconds (!!!) to live. Every process before this has created something with energy. But iron takes energy from the environs. And as a metal, it also steals electrons. Prior to this, electrons have actually helped to prop up the core because negatives repel negatives. With the energy and electrons gone, the star collapses on itself in a fraction of a second (!!!!).
Now, if the star is "small" enough (20x the mass of the sun or less), the collapse produces one of those lovely aforementioned neutron stars. The neutron stars prop themselves up because of something called "neutron degeneracy pressure", which for our purposes, simply means that it's a pressure that makes it extremely difficult to collapse any furter.
However, if the star is even larger than 20x, it now has enough energy to overcome the degeneracy pressure and produces a black hole. (Warning: over-simplification in the next sentence.) Either way, the collapse of the star is so violent that it produces a shockwave and a later explosion that sends all the star material (that's still collapsing inward at this point) outward into the universe with dozens of times more energy than our sun will produce in its lifetime (!!!!!): A type-II supernova is born. It shines for days, or even weeks, and during that small period of time, it outshines whatever galaxy it sits in. In 2016, astronomers observed a supernova explosion that happened 10 billion light years away! Remember: That supernova came from one single star. And to give you an idea of how far that is, the universe as we know it is 13.8 billion years old. So the light from that supernova had been traveling for most of the existence of the universe before some of its photons hit an astronomer's telescope one day (!!!!!!).
Aside: The first few moments of a supernova explosion are so hot that they allow fusion of the heaviest elements we know of. The "boom" sends those heavy elements through the universe at near-light speed. This is the only way we know that elements are made. What does this mean for you? It means most of what we see on Earth was once created in the fiery crucibles of supernovae.
What can black do for you?
The type of black hole we've been talking about is called a "stellar mass" black hole, and it's called that for obvious reasons: It's not that far off from the mass of a star. If that black hole has food (ie, matter) to "eat", it grows in size. Once it gets past a few dozen or so stellar masses, it's now called an "intermediate mass" black hole. (Strangely, no one's ever detected one.) At the 10,000-stellar mass size, it now becomes a "supermassive" black hole.
Why do we care about sizes? Because every galaxy we've ever studied has shown to have a supermassive black hole in it, including our own, and there's a good possibility that they are somehow involved in the formation of our own galaxies.
Also, different sizes will do different things to you before or while they inevitably kill you. (Yay!) A smaller black hole still has enormous strength, but it has something larger black holes don't have: tidal forces. What this means is that if you were to fall head- or feet-first into a black hole, the force at one end could be millions of times stronger than at the other end, turning you into a miles-long strand of spaghetti. The literal scientific term for this is "spaghettification".
Regardless the size of the black hole, one thing will always happen to you: As you fall in, anyone looking at you would see you get slower and slower and never actually fall into the black hole, or past the so-called "event horizon" (actually, that was an oversimplification: as you get closer to the black hole, the light waves bouncing off of you get stretched, themselves, turning you red until you disappear into infrared and further out of human vision -- so they actually won't even see you not into the fall into the black hole). (Whaaat?!) More back story: There's a little-known theory called Einstein's theory of general relativity. Pages and pages can be written about it, and if you feel like reading about these things (and I say this with no sense of sarcasm), go check out Wikipedia. But what we're going to steal from it is the idea that as you get closer to another mass, time actually slows down for anyone watching you. (To you, nothing changes.) If this is an ordinary mass like another person or even a planet, not much noticeable is going to happen. But if you get close to something like a neutron star or a black hole, that's where things get funky.
Once you fall into the black hole, nobody knows what happens there. Why? We don't have physics to describe what happens there. General relativity very well describes the macro world we see. Quantum mechanics describes the nano world we don't see. But you can't use either one to describe the other world: In the world of quantum mechanics, things are much, much weirder than you'd ever expect (or understand, for that matter). In a black hole, when things get infinitely small and infinitely dense, neither fully applies, and the two theories are so disparate that they can't be unified (again, going back to my point that you can't apply one theory in the other theory's world). To understand what happens in a black hole will also help us to understand what happened during the Big Bang, when all of the universe existed in a similar space of infinite density.
Where Stephen Hawking fits in
In the "Black holes are not" section, I said that black holes are not actually black. That might seem crazy, because as we all know, light and everything else can't escape from black holes.
That is all true, but if something were "born" from outside the event horizon, it could still escape because it's not yet past the event horizon. Quantum mechanics posits that pairs of tiny, subatomic particles -- one with positive mass and one with negative (yes, negative) mass pop into existence out of nowhere and annihilate each other nearly instantly. If you've never heard of this before, I'm sure you're calling "bullshit" right now, and that's understandable. Recall that earlier, I said that the world of quantum mechanics makes no sense to us. Tada! But this has been proven with experimentation: There is an experiment wherein you put two non-charged plates nanometers apart, so close together that virtual particles cannot appear between the two plates. However, they can appear on the outside of the plates, and sure enough when they do, they produce a positive pressure that pushes the two plates together.
Hawking wondered, what would happen if a pair of particles were to be born right outside of a black hole? The positive energy particle would have enough energy to escape, however the negative energy particle wouldn't and it would fall in. The stream of virtual particles leaving the black hole is called "Hawking radiation" (so you see, black holes are not entirely black). Amazingly, this would actually make the black hole lighter, and any inactive ("non-eating") black hole is actually slowly evaporating itself away over the eons as these negative mass virtual particles fall in until one day, they explode themselves out of existence. (Hence, my earlier bullet point that black holes are not forever.)
But wait, there's more! One of the un-violatable laws of the universe is that information is never destroyed. By "information", we mean the position and full set of properties of every particle in the universe (spin, charge, temperature, velocity, what it likes to eat for breakfast, etc). With all of this wealth of information, you should be able to reverse all the properties and run the universe backwards in time. But if black holes simply disappear into the ether, that information is lost, creating the Information Paradox. We don't yet have an answer for this, though we do have leading theories.
Conclusion
If you're not a physics enthusiast and you're reading this, first, congratulations! This was some pretty dense material. I hope I made it at least a little bit interesting with my terrible sense of humor. But I also hope that it was interesting enough, on its own, to withstand the length of this blog post.
If you're new to physics, it's easy to read this with a lot of skepticism. Just the quantum mechanics alone is enough to make you cry "bullshit". For me, it's taken me years to amass and also absorb the information necessary just to write this blog post. Be assured, though, that these ideas aren't simply tossed around and accepted. The great thing about science is that when you publish a paper in a scientific journal, your scientific rivals get to look at it and poke at it and pull it apart. Donald Trump may do the best to hide the truth from...well, everyone, but in science, there is no hiding. Science doesn't care how famous you are or how much money you make or how popular you are. In fact, in the stories of black holes, there was a very famous fight between Stephen Hawking and another physicist, Leonard Susskind, over the information paradox (Wikipedia humorously calls this "the black hole war"). Einstein was famously wrong when developing his theory of general relativity; he added what's called a "cosmological constant" to introduce a force to counter-act gravity in his equations because gravity would cause the universe to collapse, and as we "all know", the universe is static and unchanging. Wrong!!! As it turns out, the universe is far from static: In fact, it's expanding faster and faster. When this was discovered, Einstein called his cosmological constant his "greatest blunder".
So, there are two points to make: 1) Everything I've said in this blog post has either been demonstrated through observational evidence, or in the absence of evidence, simply hasn't been disproven, yet. 2) Tomorrow, some paradigm-shifting information or breakthrough could surface, causing us to re-think much of this. But nonetheless, any observational evidence we've seen would still need to be explained in one way or the other.
What we know, and what we still don't know about black holes makes them one of the most fascinating objects to study. They not only stretch one's body to infinity; they also stretch our human capacity to think, reason, and understand. And I can't wait what else we have to learn from them in the future.
I saw Stephen Hawking in college. He gave a basic physics lecture to the audience, although at the time I didn't know as much as I do now so it was pretty cool stuff then.
It was painstaking watching him answer questions from the audience. Took forever for him to get out his answers, but even then he was funny and charismatic and darned if he didn't captivate all of us.
The world owes so much to him. Einstein may have predicted black holes, but it was Stephen who gave us Hawking radiation (who would've guessed that Stephen Hawking would've discovered Hawking radiation?).
It's too bad he didn't survive to see quantum mechanics and general relativity married.
The world is a lesser place without him, although I'll take solace knowing that matter/energy is neither created nor destroyed.
