![]() The spiral arms radiate out from a central bulge or core, full of older stars. Spiral galaxies have flat disk-like shapes with spiral arms containing lots of molecular gas and dust from which new stars are made. It's located 2.5 million light-years away, making it the nearest big galaxy to the Milky Way. ![]() This is the Andromeda galaxy M31, the largest galaxy in our local group which includes about 45 galaxies.Īndromeda is a spiral galaxy spaning some 260,000 light-years and containing over a trillion stars. There are also some very rare and unique galaxy types that don't appear to fit into the main groups at all. Each of these main groups can be further divided into several sub-types. Galaxies come in four main types: ellipticals, spirals, lenticulars, and irregulars. Or did the supermassive black hole form first and then attract matter around it which eventually formed a galaxy? If the galaxy came first, then the supermassive black hole formed in the gravitationally densest part of that galaxy which is the centre. Scientists are still trying to work out which came first, the galaxy or the supermassive black hole. Most if not all galaxies have supermassive black holes millions to billions of times the mass of our Sun in their centres. ^ to top At the heart of every galaxy is a black hole Galaxies also form stars through a process called accretion which happens when a cloud of cold gas and dust starts to gravitationally collapse. These interactions often also trigger starburst, but can also push gas out of a galaxy. The gravity from these close encounters pulled and tugged the Large Magellanic Cloud all out of shape, giving it the appearance of an irregular galaxy. The Large Magellanic Cloud lost its barred spiral shape after getting too close to the Milky Way and another neighbouring galaxy called the Small Magellanic Cloud. Our Milky Way galaxy has gravitationally disrupted a nearby galaxy called the Large Magellanic Cloud, which was a barred spiral galaxy. ![]() Right now the Milky Way is cannibalising a smaller galaxy called the Sagittarius Dwarf Spheroidal Galaxy.Īnd in about 3.75 billion years from now the Milky Way itself will collide with the much bigger Andromeda Galaxy, forming a giant new elliptical galaxy.Īnother way galaxies can change their appearance is through gravitational tidal interactions with other galaxies - this results in stars smeared over large areas and can disrupt a galaxy's spiral arms. When a small galaxy gets sucked into a bigger galaxy it's called galactic cannibalism.Ĭollisions between galaxies can trigger starburst, but it can also push gas out of a galaxy in a process called quenching which can stop new stars forming. One of the ways galaxies grow is by merging or colliding with other galaxies. Galaxies making lots of new stars at once are called starburst galaxies. They're usually far less massive and far less ordered in appearance, with astronomers often describing them as 'train wrecks.'Īs galaxies evolve, they convert more and more of their gas into stars, giving them a bluish hue. Galaxies in the first few hundred million years after the Big Bang look very different to galaxies today. (Artist's impression of CR7: the brightest galaxy in the early universe.
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