麻豆淫院

How can astronomers pierce through the interstellar fog of the Milky Way鈥攏ot to study distant objects, but to understand the fog itself? It just takes a little light.

On January 12, 2003, NASA launched the CHIPS satellite. That's short for Cosmic Hot Interstellar Plasma Spectrometer, and it is probably, let's be honest, a backronym where they came up with the name first and then they filled in all the gaps later.

Anyway, its goal was to study something called the interstellar medium. This is the stuff between the stars. It's a super-hot plasma, but it's also incredibly thin. It's so thin that it would register as a vacuum in a laboratory on the Earth. But there's a lot of volume between the stars, and so it adds up.

You can't really see it. You can't really detect it. The closest thing you can get to seeing something like the interstellar medium is called zodiacal glow. Just after sunset, if you're looking in that direction and the sky looks nice and dark, you might see a triangular-shaped fuzz of light stretching into the sky. That's from sunlight scattering off of all the little bits of dust grains in our solar system.

The interstellar medium is like that, only more so. Most of the interstellar medium is hydrogen and helium. There are also some heavier elements, and then there's also dust like we have in the solar system.

It's super-hot, super-thin, and just kind of there. It's this fog that sits between all the stars, and all the stars swim through this fog. And CHIPS was launched to study this fog because the interstellar medium is so hot that it's glowing. It's emitting a faint amount of ultraviolet radiation.

It's not a lot of radiation, because there isn't a whole lot of interstellar medium to produce it, but it's there. But once you add up enough volume, there should be more than enough accumulate medium to make an appreciable glow.

So that's what CHIPS set out to do. And it totally failed. Not in the sense that the mission failed due to a malfunction. It failed because it couldn't detect any significant ultraviolet radiation from the interstellar medium.

A null result.

That told us that there wasn't nearly as much of the interstellar medium around us as we initially thought.

Something fishy is definitely happening in the vicinity of the solar system. And so astronomers developed a more detailed plan to map out the interstellar medium using something called the column density. This is a measure of the total amount of gas and dust along a line of sight.

Instead of looking for ultraviolet radiation, they searched for very specific spectral fingerprints of ionized gas. By looking in many directions, they could build up a three-dimensional map of the density of gas surrounding us.

Over the decades, a picture has emerged that the interstellar medium is relatively thick in the direction of the galactic plane, but very thin and elongated within the disk of the galaxy.

So, already we know this fog that surrounds us is thicker in one direction than it is in the other. And we're finding that when we look really close to us, in our solar neighborhood, we don't see anything at all. We now call this region the Local Bubble, and it's our home.