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?
It’s a radio telescope, the largest in the world. It’s so huge that a normal support system can’t support its weight. So it’s basically suspended between three mountaintops. It’s 300 m across, which is 1000 feet. It’s huge.
This is the kind of construction endeavor that radio astronomers must try if they want to get much detail from radio waves. The radio wavelengths of the electromagnetic spectrum are really, really weak. You need huge telescopes to collect enough.
But, as ever, astronomers face the same basic problem: money.
Huge telescopes are expensive. It’s unfortunate for astronomers, but true—just think of the cost of labor of basically burying a whole valley under a radio dish.
Astronomy is a labor of love, and radio astronomy is no different.
As I covered in my last post, radio astronomy deals with the longest wavelengths of the electromagnetic spectrum (a spectrum that includes visible light). Radio waves are not sound waves. They’re radiation just like visible light, infrared, and ultraviolet.
I’ll prove to you that radio waves can’t be sound waves. We get them from space—that’s why there’s such a thing as radio astronomy. But there’s no sound in space. Why? Sound requires something to pass through, and space is a vacuum.
So, we’ve established that radio waves are just another form of electromagnetic radiation. And astronomers love to collect any form of electromagnetic radiation. We can’t touch the stars ourselves, so it’s our only chance at learning about the cosmos.
Why? Because just about everything in the sky emits electromagnetic radiation.
Everything except black holes and a couple other things…but those are topics for another day.
But electromagnetic radiation isn’t easy to collect. And radio waves are especially hard.
Yeah, it’s a bit bigger than your average radio antenna.
That’s because its job isn’t to direct radio signals to your house. It’s a radio telescope, and its job is to collect as many radio signals as it possibly can—from outer space, not from a radio station.
Radio astronomy is a tricky business. It has its advantages over visible astronomy—it certainly works better for interferometers—but radio signals are so weak, they’re hard to detect and study. Which is why you’ll never see a small radio telescope.
So, how do astronomers manage to collect and study radio emissions from the cosmos?
Imagine you have an image like this. This object is faint and faraway, so you can’t make out much more detail. You know that other stars like it—closer, brighter stars—have looked like this and turned out to be two stars, nestled very close together.
How do you figure out what you’re looking at? How do you increase the resolving power on your telescope so that you can make out more detail?
A telescope’s resolving power is limited by its size. Bigger telescopes can make out more detail on faraway objects—that’s because they can gather more light. But now, we can make telescopes that are so big their size doesn’t limit their resolving power anymore.
The atmosphere does.
We obviously can’t change the atmosphere. So how do we get around this particular predicament?