Groups Why Join? Astronomy Day. The Complete Star Atlas. Some of these cosmic behemoths can whip their stars around at over 1 million miles per hour. By Erika K. Carlson Published: Wednesday, October 23, The Largest Spiral Galaxies Astronomer Patrick Ogle was looking into the brightest galaxies recorded in galaxy surveys when he stumbled across super spirals — spiral galaxies with 10 to 20 times as much visible matter as the Milky Way.
The largest, brightest galaxies tend to be blobby elliptical galaxies rather than swirling spirals, so the finding was a surprise. Ogle is the lead author of the new study. He and other astronomers measured the properties of these super spirals and were surprised to find how fast these galaxies rotated. When one object orbits another, its orbital speed depends on the mass of the central object. Whether a planet orbiting a star or a star orbiting the center of a galaxy, it will orbit faster if the central object has more mass.
Most spiral galaxies rotate at speeds proportional to the amount of visible matter, like stars and gas, they contain. The dark matter in these galaxies also contributes to the rotation speed. But the amount of dark matter tends to be proportional to the amount of visible matter, too, so rotation speeds are still proportional to visible mass.
But super spirals rotated much faster than astronomers would have predicted based on their visible mass, meaning they actually have a much higher ratio of dark matter to visible matter. Ogle and his team think that for the most massive spiral galaxies, the buildup of dark matter might be stopping more stars from forming.
For Ogle, the finding is an exciting new way to study how dark matter behaves and affects our universe. He plans to make future observations to further investigate exactly how massive these super spirals are and better understand how they came to be. Long trips to space linked to possible brain damage. First crewed Artemis Moon landing delayed until at least Our galaxy really has a mass of more than 1 trillion suns, and extends out more than , light-years; a third of the distance to the nearby Andromeda galaxy.
All the galaxies we can see are rotating. We have written many articles about galaxies for Universe Today. We have also recorded an episode of Astronomy Cast about galaxies — Episode Galaxies. Skip to content. Like this: Like Loading The galaxy is rather huge—at least , light-years in diameter, making it the second-biggest in our Local Group of galaxies. More mind-blowing is that this mass of stars, gas, planets and other objects are all spinning. Just like a pinwheel. It's spinning at kilometers per second miles per second and takes about million years to complete one rotation, according to the National Radio Astronomy Observatory.
But why? More details below. It's worth taking a quick detour to talk about how long it takes the Solar System to move around the center of the galaxy. According to National Geographic, that's about million years. Dinosaurs were starting to arise the last time we were in the position we are today.
Scientists have mapped the spin using the Very Large Baseline Array, a set of radio telescopes. They examined spots where stars were forming and paid particular attention to those areas where gas molecules enhance radio emission, according to the National Radio Astronomy Observatory. Dubbed "cosmic masers", these areas shine brightly in radio waves. As Earth moves in its orbit, the shift of these molecules can be mapped against more distant objects.
Measuring this shift shows how the entire galaxy rotates—and can even provide information about the mass of the Milky Way. So that's all very neat, but why is it rotating in the first place? If we think back to the early Universe, there are two big assumptions astronomers make, according to How Stuff Works: there was a lot of hydrogen and helium, with some parts denser than other areas. In the denser areas, gas clumped together in protogalactic clouds; the thickest areas collapsed into stars.
The rotating disks attracted more gas and dust with gravity and formed galactic disks. Inside the galactic disk, new stars formed. What remained on the outskirts of the original cloud were globular clusters and the halo composed of gas, dust and dark matter.
A simpler way to think about this is if you're creating a pizza by tossing a ball of dough into the air. The spin of the dough creates a flat disc—just like what you observe in more complicated form in the Milky Way, not to mention other galaxies.
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