WTF is that?
Long story short, it’s a map to find your way back to Earth, should you find yourself lost amid the Milky Way galaxy.
No, seriously. The map indicates the position and rotation period of the 14 pulsars closest to Earth. It also indicates our Sun’s relative distance to the galactic center. So if you were anywhere outside the solar system, you could triangulate the position of home.
What the heck is a pulsar?
A pulsar is a rapidly spinning neutron star which emits cones of electromagnetic radiation out into space from its north and south poles. If those poles happen to point toward the Earth, we call that specific neutron star a pulsar because the radiation appears to be pulsing as it rotates.
Ok, so what’s a neutron star?
Glad you asked. Something like 98% of all the stars in the Universe are “small” or as astronomers call them, low-mass. That means they’re roughly the size of our Sun - maybe a little bigger, maybe a little smaller. That leaves a very small percentage of all the stars out there to be “big” or high-mass (roughly 8 times the mass of our Sun or bigger). High-mass stars are brighter (duh), and they live much shorter lives than their low-mass counterparts. What’s even more interesting though is that ALL high-mass stars will die spectacular deaths in something called a supernova.
Get on with it.
I’m trying, I’m trying. Ok, a supernova is an explosion that is set in motion when a star can no longer carry on a fusion reaction to offset the inward gravitational pull of its enormous mass. Fusion is taking place inside the belly of all stars, regardless of their size and it releases an insane amount of energy. In our Sun, it’s only hot enough to fuse hydrogen (the smallest element on the periodic table) into helium (the 2nd smallest element). But in the cores of bigger stars, the temperature can exceed 10,000,000,000 Kelvin – hot enough to fuse carbon, oxygen, silicon, etc. all of the other elements all the way up to iron (Fe).
My point is that as you try to fuse heavier and heavier elements, you get less energy than before. At some point, you don’t get enough outward push from fusion to counteract the inward pull of gravity. Iron just so happens to be that tipping point. Now gravity starts to collapse the core of this enormous star until the neutrons that exist within the nucleus of the iron atoms are practically touching each other. I probably should have mentioned that neutrons don’t like to touch other. So the neutrons bounce off each other and there’s recoil that shudders through the entire star with more kinetic energy than any other explosion in existence.
Wouldn’t that destroy everything?
You’d think that, wouldn’t you? Oddly enough, the iron core of this huge star is protected from the explosion, a lot like the daredevil who will sit in a box covered in TNT – the explosion goes outward, not inward, so the stuff on the inside is OK.
So the neutron star is made of iron?
Sorta. During the gravitational contraction, the electrons in the iron atoms come into contact with the protons and create neutrons (and neutrinos, but that’s more than we need to worry about right now). This means you’re left with a giant ball of neutrons. Fun fact: a neutron star is so dense that a spoonful of it would weigh more than Mount Everest!
I think I get it.
Yeah, and we’re not even close to being done yet.
That’s what makes this map so cool – it’s a simplistic representation of a crap ton of information.
If you say so.
I do, and you asked, so you’re going to listen. In physics, something called the Conservation of Angular Momentum means that if a spinning object contracts, it has to spin faster. Think of a figure skater spinning and pulling his/her arms in.
Sure, I watch figure skating.
But you get my point. We’re talking about an object with the mass of the Sun, the size of Manhattan, spinning hundreds (or even thousands) of times per second.
And the pulsing?
Almost forgot. It’s true that neutrons are neutral (no charge), but the neutron star isn’t 100% neutrons – it does have charged objects (protons & electrons). And charged objects have what’s called an electric field. And when an electric field changes (or is in motion), it creates a magnetic field. So spinning charged objects gives rise to electromagnetic radiation – or to put another way: light.
So because it’s light we can see it?
Sorta. Light has different wavelengths based on its energy. High energy light like gamma rays can be deadly to living things, but low energy light like radio waves are harmless. The rotation of neutron stars creates radio waves, so you need a special radio telescope to see them. That’s why we didn’t know neutron stars did this until the first pulsar was discovered back in 1967.
Ok, so it’s a map of pulsars. What do the little tick marks mean?
Just so we’re clear, you keep asking, I’m going to keep telling. No whining. Ever heard of binary?
Sure, Bender (from Futurama) makes jokes about binary all the time.
Close enough. Typically, we used a Base-10 numbering system, which means we have 10 numerals (0,1,2,3,4,5,6,7,8,9) and each digit in a number represents a power of 10. So, 10^0 = 1, 10^1 = 10, 10^2 = 100, and so on.
Wait, that’s what my 3rd grade teacher meant by the ‘tens’ place and the ‘hundreds’ place?
Oy. Yes, and she’d be so proud to know that you remember that.
Binary means there are only two options for each digit, 0 and 1. It’s a Base-2 numbering system, so 2^0 = 1, 2^1 = 2, 2^2 = 2, and so on. Since binary is simplest possible numbering system, astronomers figure it would be a good idea to use on map that could possibly be discovered by other life forms in the hopes that they’d understand it.
So how does binary apply to the pulsars?
Since the pulsars are rotating, they must have a period between pulses that can be timed. The tick marks are those periods written out in binary. “I - - I” would translate to “1001” in binary which equals 9 in Base-10.
How would the aliens know what that means?
There’s no guarantee that they would, but we think it’s the best chance. The other part of the map (the two circles next to each other) is a key of sorts. It represents a hydrogen atom which only has 1 proton and 1 electron (no neutrons).
Hey! I actually knew that!
Good to know public schools aren’t a total waste. Anyway, both the electron and proton have a charge, and both spin. Quantum mechanics…
Don’t worry, it’s not that bad. Quantum mechanics says that these two spins have to be either in the same direction or in complete opposite directions, there are NO other possibilities (the spins are said to be quantized for that reason).
Careful, there’s a saying that if you think you understand quantum mechanics, you don’t. No matter. Naturally, the electron and proton spins will be opposites. It takes energy to make them the same, and they don’t like being the same, so at some point, the electron will flip back to the opposite position again. Since it takes energy to make them the spin the same way, it must give off energy when the electron flips back, right?
Well, when the electron flips, it gives off light with a wavelength of 21 centimeters which means it has a frequency of 1,402 megahertz. Frequency just means “cycles per second,” so if we take its inverse, we get a time of 7.04024183647 x 10-10 seconds. In English, the EM radiation emitted by the electron undergoing this transition takes 0.0000000007 seconds to oscillate once.
You’re losing me.
I know, this is the hard part, but we’re almost there. Let’s just look at one of the pulsar lines:
This means that pulsar has a rotation period of 1178486506 times the hydrogen spin-flip emitted radiation oscillation time.
Say that 5 times fast.
So, 1178486506 x 7.04024183647 x 10^(-10) seconds = 0.8296830003 seconds. That pulsar rotates 1.2 times every second.
Just about. The relative lengths of the lines for each pulsar and their angles are all important too – they give the relative (meaning there’s no actual numbers involved) positions for where to find these 14 pulsars. So theoretically, if you can identify these pulsars from their rotation periods and you can map them all in three dimensional space, you should be able to pinpoint the one point in the galaxy where all of these distances converge – that’s Earth.
I know, right?