It certainly isn’t often that I create such a lengthy post title, that’s for sure. But given how long it’s been since I blogged, this feels like a once-in-a-while sort of moment.
A moment where, apparently, I deviate from my previous posting plan and show you an image of the blood moon, when last I knew, I was supposed to be talking about black holes.
Yeah, I know. My last post, written over a year ago (sorry!), was about what the movies get wrong about black holes. And the post that would have followed naturally from that one, which somehow got delayed for what feels like an eternity, was supposed to be about how to search for black holes throughout the universe.
Don’t worry, we’re still gonna get to that. Presumably in my next post.
However, there is a lunar eclipse coming up in less than a week, and I wanted to take the opportunity to review the science of an event I’ve already blogged about before. This way, I don’t need to spend quite as much time talking about the actual eclipse, and I can fill you in on why the freaking heck you missed out on science posts for a whole year and three months.
And can I just say, it feels really good to slip back into my old writing style? It’s odd, in a way—part of me wants to change things up a bit, as if I’m fearing some kind of judgment. I guess that’s just the effect the last year or so has had on me.
To those who don’t, it probably looks like a pretty unimpressive, blurry ring. In fact, this is the first ever image of a black hole, taken with an interferometer the size of the Earth.
If you’re a science geek, you’ve no doubt seen tons of artists’ conceptions of black holes on the internet. Most use a great deal of artistic license. Some of my favorite “images” of black holes used to be the ones that look like ripples in the fabric of space. Imagine my disappointment when I realized that’s not the case at all.
Black holes are singularities—infinitely dense places of zero radius with at least 3 M☉ (solar masses) of star stuff—surrounded by an event horizon, inside of which gravity is so strong that even light cannot escape. That’s why it’s called a black hole.
But they are not “holes” in the usual sense. They are not giant space potholes that you can easily stumble into, and you certainly don’t fall into them the same way you would a pothole.
If you’re a sci-fi fan, you’ve probably seen these in movies. And I’m guessing you’ve heard a lot about them in pop culture. The problem is, pop culture and movies don’t do a very good job of describing black holes.
First off, let me clear up a common misconception: Black holes do not act like giant space vacuum cleaners, sucking in everything around them. Describing them as “gobbling up” anything is inaccurate.
The representation in movies that bugs me the most is in J.J. Abrams’ Star Trek reboot, when the bad guy falls into a black hole and the good guys almost get pulled in with him. First of all, please…black holes do not growl. And basically none of what happens in that scene is accurate.
Neutron stars—the compact remains of massive stars that have gone supernova—are some of the most extreme objects in the universe, narrowly beaten by black holes (and, as we’ll talk about in future posts, active galaxies and such).
Dense balls of pure neutron material with diameters barely larger than Los Angeles, neutron stars have strong magnetic fields that produce beams of radiation at the magnetic poles. Their speedy rotation makes these beams sweep across the sky like a lighthouse.
When one of their beams crosses directly over Earth, human astronomers observe rapid pulses of light called pulsars.
These objects are whacky, to say the least. And there’s more…
Way back when we spent a number of posts surveying the stars, we covered binary systems. These are star systems that contain multiple stars. Imagine if our sun had a companion, and two stars rose and set in our sky over the cycle of day and night.
It might surprise you that the majority of stars in the universe are actually in binary systems. Our solar system seems to be an outlier in that regard. Most stars have a companion or two or six…
…and so do some neutron stars.
Remember that neutron stars are the collapsed remnants of massive stars that have gone supernova. If most stars are part of binary systems, then naturally, some of these stars will evolve into neutron stars and still be part of their birth system.
For those of you who missed my last couple of posts, allow me to introduce the neutron star: a stellar remnant similar to a white dwarf, but much denser, so dense that its protons and electrons have combined to form a neutron soup.
A neutron star forms from the collapsing core of a star between 10 and 20 M☉ (solar masses). Its collapse produces powerful magnetic fields and extremely high temperatures, but because it becomes so small—less than the size of Los Angeles—it is very faint and radiates away its heat very slowly.
The exception to that rule comes in the form of two powerful beams of radiation that blast away from the object’s magnetic poles. As a neutron star spins—at around a hundred times per second—these radiation beams sweep across the sky like the the beams of a lighthouse.
If these beams happen to sweep over Earth, human observers see regular, rapid pulses of light. This visual phenomenon produced by neutron stars is called a pulsar.
Now that we have a basic understanding of neutron stars and pulsars, let’s explore some of the details of how these extreme objects work.
Imagine you’re observing the sky with a radio telescope. Observing the faintest, lowest-energy photons the universe has to offer is your specialty. You study interstellar dust clouds, protostars, and lots more.
One day, though, something interesting pops up in your data. You’re looking at raw data on a computer screen, not an eyepiece of a “typical” (optical) telescope—you get all your data from the giant dish above. Strangely enough, there’s a series of regular pulses.
At first, you think it’s just “noise” from sources on Earth—like static on your car radio. But then you see it, day after day, in the same place in the sky. It’s not static. It’s real.
You wonder if this is perhaps evidence of contact with a distant civilization. Personally, I’d hope for that one. Unfortunately, more research leads to the conclusion that it’s nothing of the sort—within weeks, you find that there are several other objects in completely different parts of the sky, all emitting similar (but different) pulses.
You’ve discovered a pulsar. But…what exactly is a pulsar?
Above is a theoretical rendering of a white dwarf, the collapsed husk of a low-mass or medium-mass star. Interestingly enough, these strange cosmic objects—which begin their existence as intensely hot balls of carbon the size of the Earth—may eventually cool off and crystalize into giant space diamonds.
White dwarfs are made up of free-floating hydrogen and helium nuclei and degenerate electrons—and their mass is supported by the nature of these electrons.
But degenerate electrons, like any other material, have a specific material strength. What happens if they’ve, well…just got too much stuff to support?
This is one topic I bet you guys have been looking forward to since I first started posting about stellar evolution. Well, I won’t disappoint you!
In my last post, we covered how a massive star gets to the point of supernova. When it exhausts all the nuclear fuel in its core, iron ash is left behind—which can’t be fused or split for energy. That’s a dead end for the star, and the core begins to freely collapse…
Until a shockwave, originating in the center of the star, pushes outward. It’s stalled at first, but convection as in-falling material bounces off the dense core gives it a boost, and the star bursts apart.
Now, we’ll cover all the ins and outs of these spectacular explosions.