(SciShow Space Intro plays)   Caitlin: Being a scientist means learning how to ask good questions, and sometimes a good question can be as simple as, "What's that blue stuff?" In August of 2007, a Dutch schoolteacher named Hanny Van Arkel asked that very question. She'd recently joined a citizen's science program called Galaxy Zoo and was about to stump scientists all over the world. Van Arkel noticed a small blue smudge next to a galaxy, which turned out to be one of a whole new class of objects. And scientists still aren't sure exactly what they are or where they came from.   Astronomers launched Galaxy Zoo in July 2007, because they needed help. The Sloan Digital Sky Survey, or SDSS, had detected more than a million galaxies from the Apache Point Observatory in New Mexico, and classifying them was going to be tough. Galaxies come in different shapes, like spiral, elliptical, and irregular, and while it's relatively easy to program a computer to find a galaxy in an image, it's a lot harder to figure out what type of galaxy it's detecting. But people, it turns out, are pretty good at it. Our brains like to find shapes and patterns. The problem was that it would have taken several mind-numbing years for one person to pore through all that data and classify each galaxy, so the team set up Galaxy Zoo, where thousands of volunteers could split the time. But first, the public had to find out about the project, and one person who offered to help get the word out was Brian May, who'd just finished his PhD in astrophysics. You might also recognize him as the guitarist from Queen.     Hanny Van Arkel happens to be both a Queen fan and a science fan, and when she heard about the project, she thought it would be fun to check out Galaxy Zoo over her school break. About a week later she noticed a wisp of gas next to one of the galaxies, which the official project blog decided to call a mystery blue blob. When Van Arkel asked about it in the forum, she got the best response in science: no one had any clue what it was. One of the other volunteers started calling it Hanny's Voorwerp, which means Hanny's Object in Dutch, because Dutch is awesome and the name stuck.     Some of the professional astronomers involved in the program decided to investigate by taking a closer look with other telescopes. The new observations confirm that the smudge was really there and wasn't some weird problem with the original telescope. They also found out that the mystery blue blob was actually green. The SDSS images were false-colored, meaning that each part of the image was assigned a different color depending on which particles were detected. The blue of Hanny's Voorwerp meant that it contained oxygen, but without the false color, it was green.     Now that they knew that the Voorwerp was real, the team could look for others. In 2011, they published a list of 19 more glowing gas clouds just outside of galaxies. These objects have been subjected to a lot of scrutiny to try and pin down what they are. Hanny's Voorwerp in particular has been studied using many different observatories, like Hubble and the Swift Gamma-Ray Observatory.     Eventually, astronomers came to the conclusion that objects like Hanny's Voorwerp are special types of light echoes called quasar ionization echoes. Just like how sound echoes off of distant walls, light can bounce off of gas clouds in space. The original source of a Voorwerp's light is probably a quasar, an active supermassive black hole at the center of a galaxy. As the quasar sucks in gas, it heats up, producing an incredible amount of light. The light usually blasts straight out of the galaxy, but sometimes, a small galaxy will merge with the quasar's host galaxy, leaving behind twisted, stretched out clouds of gas, a Voorwerp. The quasar's light travels unimpeded for tens of thousands of years until it hits the gas cloud. Some of it bounces off, and the rest is absorbed by the particles in the cloud. All that extra light energy knocks out some electrons, ionizing the particles which emit light as they go back to normal. The Voorwerp keeps shining long after the quasar has finished its meal and gone dark.     But a more recent study published in March in the Astronomical Journal throws an extra wrinkle in the theory. An international team of astronomers pointed Hubble at a whole set of these Voorwerps and found that a single quasar probably isn't bright enough to create the echoes. The new results suggest that it may take a more extreme environment, like a closely orbiting pair of supermassive black holes to give the quasars enough gas to make a Voorwerp.     Astronomers are still working out the exact physics behind these light echoes, but this entire class of objects wouldn't have been discovered if it hadn't been for the curiosity of citizen science volunteers. So thank you, citizen science volunteers, and thank you for watching this episode of SciShow Space. If you wanna help support the show plus get access to cool stuff like blooper reels and our monthly Google Hangout, just go to patreon.com/scishow.     (SciShow Endscreen plays)