Our solar system is just a small part of the billions of galaxies that make up the universe. Every galaxy has its own set of stars, planets, and other celestial objects that orbit it.
These things all orbit around the center of the galaxy, which is where the gravity forces them to move in a predictable way. However, there are some places in a galaxy that can be chaotic with stars and planets being flung around all the time.
Stars
Astronomers have been looking for evidence of solar systems outside our galaxy, the Milky Way. They have found evidence of many, but haven’t been able to find all of them.
A major problem is that stars in distant galaxies blur together so much in telescope images that it’s difficult to find planetary systems around them. To overcome this, scientists are using an innovative method to look for planets in star systems called X-ray binaries.
The Milky Way is just one of billions of galaxies in the universe. It’s a whitish spiral galaxy and contains a lot of light, including the brightest star in our sky.
Our Solar System consists of eight planets orbiting the Sun and a large halo of asteroids, comets, and other small icy objects. It was formed about 4.7 billion years ago when a cloud of gas and dust was pulled into clumps by gravity. The clumps eventually formed the Sun and then the planets.
Planets
Planets orbiting a star can be either rocky (the four inner planets, Mercury, Venus, Earth and Mars) or gaseous. The gaseous planets are made of heavier materials that are attracted to the star’s gravity. The rocky planets are smaller and have a rocky core.
Scientists think that our solar system, which is made of eight planets and many moons, was formed 4.568 billion years ago. When the Sun was young, it flung out energy and particles in a steady stream, called stellar winds.
These winds blew off most of the gases from the planets closest to the Sun, leaving them smaller. The planets farther from the Sun remained gaseous, but had small rocky cores.
In the past two decades, scientists have discovered thousands of extrasolar planets — planets that exist outside our solar system and orbit other stars. These planets come in a variety of sizes and orbits. Some are giants hugging close to their parent stars; others are icy and some are rocky.
Stardust
Stardust (also referred to as comic dust) is the largely unformed matter that formed before planets, moons, and other celestial bodies were created. These particles are often coated with ices, such as water, methane, or ammonia, and may contain some chemical trace elements.
The most common sources of stardust are extremely hot gasses ejected from stars or supernova explosions. However, dust is also found in circumstellar dust clouds, which form around other galaxies.
Another source of stardust is interstellar dust that forms in the outer regions of the universe. It can be made of a wide range of different substances, including carbon, silicon carbide, amorphous silicate, polycyclic aromatic hydrocarbons, and water ice.
Until recently, finding planets outside of our own galaxy has been difficult. That’s because distant stars blur together, making it harder to scout out individual systems of planets in telescope images. But now, astrophysicists have developed a way to find planets in X-ray binaries, or pairs of stars that emit extreme radiation.
Black Holes
Black holes are massive objects at the centers of galaxies that trap everything inside them. Their intense gravity bends all particles and light paths inward, making it impossible for anything to escape.
These black holes have two sizes, which scientists call’stellar mass’ (a few times the mass of our sun) and’supermassive’ (millions or billions of times the mass of the Sun). Supermassive black holes are common at the cores of galaxies.
If a star gets too close to a supermassive black hole, it can be consumed by the monster. Or it may get flung out of the galaxy altogether.
In the last century, astronomers began to realize that there were black holes out there in the universe. They found evidence of their existence in quasars – faraway stars that emit powerful gamma rays and other energetic radiation.
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