Many of the worlds we see around us are made of dark matter. We know it by the name “planetary Matter” and it consists of many different kinds of atoms, but most of us know it as dark matter because it shows up very dimly in our pictures of celestial bodies. The fraction that makes up the planetary matter is called “metallicity.” If you look up at the stars and the galaxies, they all have metallicity. The fraction that makes up the dark matter in spiral galaxies is about twice as massive as metallicity.
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So what fraction of the mass of spiral galaxies is in dark matter? Astronomers don’t know exactly, but they think it’s close to ten percent. A recent study found a clue that would imply there’s a lot more dark matter in our local universe than most people realize. It was a research that used data from NASA’s Very Large Telescope. A telescope like this can only see things with a very tiny amount of energy, which makes it very sensitive to changes in energy levels near very faint objects. That’s when it noticed a slight shift in the distribution of energy as a result of a galaxy’s spin.
The shift was small, about two percent, but astronomers were astonished at what they found. They had used a different technique to detect the effect of gravity on the disk of the galaxy, and the shift was quite remarkable. This means the expansion of the disk of the spiral arm would be greater near the central area than it is farther out. That would mean there is less matter in the center of a galaxy, and it is possible that this contributes to why it’s spiral shape is so unlike that of other kinds of globes.
So, what fraction of the mass of spiral galaxies is in dark matter? It’s not quite known yet, and there are a number of different ways to calculate it. One of them is to look at the properties of gravity. Because a galaxy is made up of many compact bulges, it will tend to pull on each of those bulges, pulling on its own gravity in the process.
Another way is to look at the distribution of dark matter – how much is in the halo around stars, and how much is in the very center? While astronomers don’t know exactly what percentage of the mass of a spiral arm is in this “varying” cloud of dark matter, they do know that there is less towards the inner part of the arm, and more towards the outer bulge. This suggests the extra dark matter that makes up a galaxy is concentrated in a particular part of its disk, and that it is probably making up more of that mass than can be seen by telescopes.
If you take one of the spiral arms as a model, you get a beautiful, fuzzy image. But that image can also be very distorted. Because the inner portion of the arm is very hot, it distorts the map of the spiral, causing what we call “regression.” Another way to examine what fraction of the mass of spiral arm is in dark matter is to look at other similar spiral arms. If the other arm has fewer stars, or if the other arm is tilted towards the mid-range of the spiral (the inner portion) more, it may suggest that there is less dark matter present. Conversely, if the other arm is very cold (ice cold) it may suggest that there is more dark matter, making up a greater portion of the spiral.
{T, what fraction of the mass of spiral galaxies is in dark matter? | dark matter | mass | fraction | matter?) A third way to examine what fraction of the mass of spiral arm is in dark matter is by observing supernovae explosions. These explosions are not caused by normal celestial objects, but by very high-energy physics called “supernovae.” The explosions occur when a galaxy is going through a merger with another very large galaxy (or a black hole). Since supernovae are made up of very high energy physics, they have a very strong pull on the material around them, and as the material is pulled away, it pulls on the dark matter even more, creating a much dimmer signal that the explosion is taking place.
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{T, what fraction of the mass of spiral galaxies is in dark matter? | dark matter | what fraction of the mass of spiral | fraction | | dark matter?) There are a number of theories out there that explain the properties of dark matter, but none are mathematically precise. The best that we have so far isometrics, which shows that it is a very diffuse substance, spread out over a large area. So it is hard to say what fraction of the mass of spiral arm is in dark matter, although astronomers are not looking very hard at the skies. Until someone proves otherwise, there will be no surety as to what fraction is in Dark Matter.