You might think spiral arms form because, due to gravity, stars close in to the center of the galaxy orbit faster than stars farther out, so a spiral pattern naturally appears. The spectacular spiral galaxy M61, observed by the 8.2-meter Very Large Telescope. Right away that tells us something about big, bright galaxies! Even the simplest results are important for example, they found that 92% of the galaxies classified are spiral or elliptical, while the remaining 8% are irregular or peculiar. More than 250,000 large, bright galaxies were looked over by 160,000 people, who answered straightforward questions about them. In this case, Galaxy Zoo presented people with data from the Sloan Digital Sky Survey. The work is actually fun, and only involves a simple web interface. Studies have shown that if enough people go over the data, overall the results (when checked by professionals) are quite accurate. However, it turns out that non-astronomers can do a pretty reliable job on certain analysis tasks, like, for example, looking at a picture of a spiral galaxy and determining whether the arms are tightly wound or more open. For example, modern surveys of the sky return so much data it’s impossible for just a few astronomers to sit down and grind through it. This comes from Galaxy Zoo, a "citizen science" project that lets the public make simple analyses of real data. NGC 1398, a barred spiral galaxy that is, quite simply, gorgeous. Now, though, new observations have thrown a monkey in the wrench with all this. If there's a galaxy that didn't quite fit, astronomers usually used the arm structure to place it in the diagram. For example, one might have a small bulge but tight arms, or another with a large bulge and fairly open arms. It's done a decent job, but there have been some galaxies that don't fit the pattern. There have been other ways to do this, but Hubble's tuning fork has been more or less the standard for a century now. Those became the stem of the fork, with the two tines being the spirals from Sa to Sc on one and the barred spirals on the other. On one side were elliptical galaxies, which ranged from circular (called E0) to more stretched-out (up to E7).
Hubble created what was called the tuning fork diagram to describe all this. Credit: Karen Masters, Sloan Digital Sky Survey But new work shows this diagram may be obsolete. Spiral galaxies go from big bulges and tight arms to small bulges with widely flung arms (with a parallel row for barred spirals). The Hubble Tuning Fork diagram classifies galaxies according to shape and structure. These are called barred spirals, and they appeared to have the same structures as regular spirals otherwise, so they were called Sba to Sbc. There was also a third structure, called a bar, which looks like a rectangular or lozenge-shaped feature across the middle of the galaxy. Also, Sa galaxies tended to have well-formed continuous arms, and Sc ones have clumpier, less well-defined arms. Hubble and his team classified them this way, too, with the former called Sa and the latter Sc galaxies, with Sb galaxies intermediate between the two. Galaxies with big central bulges had tightly wound spiral arms, while ones with smaller bulges had more open arms. Moreover, there appeared to be a spectrum of these galaxies' shapes, from small bulges to big ones. Spiral galaxies (the ones with spiral arms) had two major components: the arms themselves, and a central bulge of stars from which the arms appeared to emanate. But they fell into four broad categories: elliptical, spiral, irregular, and peculiar. Once astronomers started mounting cameras on big telescopes in the late 19th and early 20th centuries, they found that galaxies - which for the most part look like small fuzzy patches to the eye - have a staggering variety of shapes. If you can sort them in some way, you can start to gain insight into them. Instead of being semi-permanent features of galaxies, they may instead actually wind themselves up, disappear, and reform again!Ĭlassification is a natural first step when you have a collection of objects and you're trying to figure them out. The consequences of this are as dramatic as they are cosmic: It implies very strongly that the way we've been thinking about how galaxies form and maintain spiral arms is also wrong.
Some big news from Galaxy Zoo: It's looking very much like a classic classification scheme for galaxies - first dreamed up by Edwin Hubble himself! - may be, um, wrong.
0 kommentar(er)
