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Galaxies are groups of stars and other space objects held together by gravity. There are over 100 billion galaxies in the universe, each featuring beautiful structures that can be seen in telescope images taken from the distant universe.
“At the most basic level, you can think of a galaxy as a collection of stars, gases and black matter all of these are gravitationally related to each other, “said Jenna Samuel, a doctoral student in astrophysics at the University of California, Davis.” What we imagine as a typical galaxy is primarily the bright part – the stars – that is embedded in it. a halo of dark matter, which extends much further. ”
The different parts of a galaxy constantly interact with each other to give a galaxy its shape, Samuel told Live Science. Dark matter provides most of the mass, maintaining it all using gravity. But stars also shape a galaxy – their heat blows around gas and dust, and when stars die in spectacular supernovas, they scatter matter near and far.
“A galaxy is really an evolutionary unit of all of these components,” said Samuel.
Related: The 15 strangest galaxies in our universe
Earth and our solar system are in the Milky Way, a large spiral galaxy containing between 100 and 400 billion stars. These appear as a strip of light across the night sky that looks like spilled milk, so the ancient Romans called it the Milky Way, which means Milky Way in Latin.
Almost all known galaxies have a supermassive black hole at its center, which also plays a role in determining the characteristics of the galaxy. When the black hole feeds on the surrounding gas and dust, the gravitational beast consumes so much material that it can smother star formation, Samuel said. Instead, the gas and dust that would typically go into making stars fall into the mouth of the supermassive black hole.
Huge jets of energy often shoot out from the active power supply of supermassive black holes, Samuel added. These jets can heat the surrounding material, which also prevents the material from collapsing to form new stars.
The supermassive black hole at the center of our Milky Way galaxy is not particularly active at the moment. “It’s in a scary phase right now,” Samuel said.
What are the different types of galaxies?
The Milky Way is a spiral galaxy, which means it’s flat, tall, and has multiple arms that spiral around a central bulge, Samuel said.
Spiral galaxies form stars at a moderate rate and are generally similar in mass to the Milky Way. Including all the stars, gas, dust and dark matter, a spiral galaxy is roughly 1,000 billion times the mass of the sun, Samuel said.
Some of Samuel’s favorite galaxies, which she studies in her research, are dwarf galaxies. These are much less massive than spiral galaxies and do not have their ordered structure. “They have an irregular shape – they look like spherical spots,” Samuel said.
Related: Why do galaxies have different shapes?
Most dwarf galaxies orbit larger galaxies the size of the Milky Way. Many dwarf galaxies erupt with star formation, Samuel said. They are generally between 10 million and 1 billion times the mass of the sun, depending on the Swinburne University of Technology in Melbourne, Australia.
Another type of galaxy is massive elliptical galaxies, which are much larger than the Milky Way. “They look a bit spherical, egg shaped,” Samuel said. “Their stars are going to be older and the galaxy will have stopped forming new stars a long time ago.” Elliptical galaxies are heavyweights, often reaching 100,000 billion or even 1,000 billion times the mass of the sun, she said.
Which galaxies are closest to us?
One of the known galaxies closest to the Milky Way is a small orbiting companion called Sagittarius, Samuel said. Sagittarius is an irregular dwarf galaxy, located about 70,000 light years from Earth, according to Nasa.
“Sagittarius is so close to the Milky Way that it is being disrupted and merging with it,” said Samuel, meaning that the incredible gravity of our galaxy is tearing apart the smallest entity and consuming its components.
An even closer galaxy named Canis Major Dwarf is located just 25,000 light years from Earth, but it has become so disturbed by the Milky Way that many of its stars are already scattered across the night sky, according to Swinburne University. Over the next billion years, Canis Major will completely merge with the Milky Way.
Related: Dark energy camera takes hyper-detailed images of nearby dwarf galaxies
Many other satellite galaxies orbit the Milky Way, Samuel said, much like the planets around the stars. Two of the most famous companion galaxies are the Large Magellanic Cloud and the Small Magellanic Cloud, which are only visible from Earth in the southern hemisphere. The Large Magellanic Cloud is 179,000 light-years away from the Milky Way, while the Small Magellanic Cloud is 210,000 light-years away, according to Nasa. One day, they too will merge with the Milky Way.
The closest main galaxy to ours is called Andromeda or M31, and it’s a large spiral galaxy about 2.5 million light years away, Samuel said. The pull of gravity brings the Milky Way and Andromeda closer together, and research suggests they will collide in about 4.5 billion years, Previously reported live science.
How are galaxies formed?
Most galaxies are billions of years old, Samuel said. No one knows exactly when the first galaxies were created, but telescope observations suggest that at the start of the universe’s existence, there were only small, dwarf-sized galaxies. Large galaxies like the Milky Way and those more massive than it have formed over time from many smaller galaxies that have come together.
Determining exactly when the Milky Way formed is an open area of study, Samuel said. Recent simulations suggest that our galaxy probably got about half of its current mass through mergers around 7 billion years ago. “This is when we really see something that starts to look like the Milky Way,” she said.
Related: A massive disk galaxy could change our understanding of the birth of galaxies
Elliptical masses are formed when several spiral galaxies come together. Astronomers primarily see these galaxies in dense areas of the cosmos, where many galaxies have crashed during the lifetime of the universe, Samuel said.
How many galaxies are there?
Another area of active research is determining the number of galaxies in the observable universe. “The sure answer is that there are hundreds of billions of them, at least,” Samuel said.
Related: Scientists just mapped 1 million new galaxies in 300 hours
Astronomers count galaxies by raising a telescope over a dark patch of the sky for a long time. They count the galaxies they can see, then determine how many more might exist based on the limits of their telescope, Samuel explained. But this method is limited and incomplete, which means there may be many more galaxies than scientists predict.
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