by Although our telescopes have captured some real amazing images of the Milky Way, astronomers have only a vague understanding of our home galaxy. It took a lot of work to even get that sketch, and it’s amazing what we managed to learn from our limited vantage point.
Here on the surface of the Earth, the The Milky Way Galaxy appears to the naked eye as a nebulous band across the sky. Although the true nature and location of the Milky Way has long been debated by astronomers and philosophers, the great astronomer, physicist and all-round wonder. Galileo Galilee He was the first to discover the true nature of the galaxy: the number of stars is so small that their light mixes together. In the mid-1700s, the philosopher Immanuel Kant correctly guessed that the Milky Way was a rotating disk of stars, and because we were embedded in that disk, it appeared to us as a band. A few years later, the astronomer William Herschel tried to world mapwithout much success.
It wasn’t until the early 1900s that we began to piece together the true nature of our galaxy. That’s when the astronomer Edwin Hubble discovered that the Andromeda Nebula was, in fact, the Andromeda galaxy, an “island universe” that sits millions of light years away. The Milky Way was just a nearby disk of stars. It was most of our own galaxy, and thus our galaxy took the name of that familiar sky feature.
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Observations of other galaxies helped us piece together what our home galaxy looked like. Most disk galaxies host spiral arms and a dense central bulge, so it is natural to assume that the Milky Way also has those features. But mapping the Milky Way directly is an extremely challenging task. For one, it’s big—about 100,000 light-years at its widest point. And there’s a lot of stuff in there — somewhere between 100 billion and 400 billion starshundreds of thousands of star-forming regions, and countless planets, black holes, neutron stars and many others. Surveys of even small parts of the Milky Way therefore require huge amounts of resources.
And then there is dust. Hanging out in interstellar space, the moving property is dimming and scattering light dust. Because we are embedded in the Milky Way, the further we try to look, the more our view is obscured by dust. Even the most powerful telescope in the world the regions on the other side of the galaxy cannot be examined directly.
So, to map the Milky Way, researchers use many types of observations and combine them with comparisons with other galaxies and clever theoretical modeling to piece together a complete picture.
For example, globular clusters orbit the center of the Milky Way in a roughly spherical arrangement. By plotting their positions in three-dimensional space, we can determine where the center is — about 25,000 light-years away.
We can also examine the motions of the stars as they orbit the center using our understanding of it gravity to model what the heart looks like. It is through this technique that we think our galaxy is a “barred” spiral – the core is elongated, and perhaps even peanut-shaped. This is confirmed by comments that show that there is a certain type red giant star which is located near the core is divided into two populations and the infrared light coming from the core is not symmetrical.
The IS Gaia spacecraft, launched in 2013, has one main mission: to create a census of as many stars as possible, recording their distance, motion, brightness and color. To date, that mission has cataloged nearly 2 billion stars, which, while impressive, still only represents about 1% of all the stars in the Milky Way.
However, that gives astronomers a huge trove of information about our local patch of the galaxy. Besides providing an accurate map of our Galactic neighborhood, this data can be used as a baseline to compare other, much narrower but deeper surveys and contrast to look for anything suspicious that might help us map the build the biggest galaxy.
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Take the spiral arms. Despite their dramatic appearance, they are only about 10% denser than their surroundings. Instead, they appear visually striking because they are regions of active star formation, containing many large, bright newly formed stars. Because we have a detailed map of our local galactic patch, not all of which are active in star formation, we can look for higher concentrations of star formation to sketch the spiral arms.
Through these techniques, we know that the Milky Way has at least two prominent spiral arms, and those arms are anchored to a central core like a giant S-shaped bar or peanut. Beyond that, however, things are a little more obscure. The galaxy might have two extra arms of medium intensity, or just a tangled mess of spurs and branches. Any “map” you might find of the Milky Way is largely conjectural and likely to change every few years as we improve our techniques and gain a better understanding.
