Beyond Our Solar System
All of the stars in the Milky Way orbit a supermassive black hole at the galaxy's center, which is estimated to be four million times as massive as our Sun.
Our Sun is one of at least 100 billion stars in the Milky Way, a spiral galaxy about 100,000 light-years across. And where are we in the Milky Way? Our Sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms.
The stars are arranged in a pinwheel pattern with four major arms, and we live in one of them, about two-thirds of the way outward from the center. Most of the stars in our galaxy are thought to host their own families of planets.
The Milky Way galaxy is just one of the billions of galaxies in the universe.
The universe is a vast expanse of space that contains all of everything in existence. The universe contains all of the galaxies, stars, and planets. The exact size of the universe is unknown. Scientists believe the universe is still expanding outward.
Ten Things to Know10 Need-to-Know Things About the Universe
1
Big Discovery
Edwin Hubble’s study of the stars revealed our galaxy — once thought to be the entire universe — is actually one of billions in an expanding universe.
2
Small Matter
Ninety-five percent of the Universe is dark energy and dark matter. The rest — everything on Earth, all the planets and stars and everything else — makes up the remaining five percent.
3
A Lot of Nothing
Our Universe is mostly empty space. Galaxies and clusters of galaxies that make up the visible universe are concentrated in a complex scaffold that surrounds enormous empty spaces.
First Image of a Black Hole
4
Cosmic Neighborhood
The Milky Way galaxy is in the Local Group, a neighborhood of about 30 galaxies. Our nearest major neighboring galaxy is called Andromeda.
5
More Planets Than Stars
We know of thousands of planets — called exoplanets — orbiting other stars in our galaxy. When you look up into the night sky, every star you see has, on average, at least one planet.
6
Common Spiral
About two-thirds of the known galaxies are spiral-shaped like our Milky Way galaxy. Most of the rest have elliptical (oval-like) shapes, and a few have unusual shapes like toothpicks or rings.
7
Many Galaxies
Hubble Space Telescope observations (pictured) of a tiny patch of space (a fraction of the diameter of the Moon) revealed more than 5,500 galaxies.
8
Is Anybody Out There?
Scientists are searching for other planetary systems could have the potential for life. So far, Earth is still the only planet known to harbor life.
9
No Escape
There is a supermassive black hole at the center of our galaxy. A black hole is a great amount of matter packed into a very small area, which results in a gravitational field so strong that nothing—not even light—can escape.
10
Billions and Billions
There may be a hundred billion galaxies in the Universe. A galaxy is full of stars: Our sun is just one of at least a hundred billion stars in our own Milky Way galaxy.
Thousands of Galaxies
FAQ: How Big is Space?
We'll let our colleagues in Exoplanet Exploration (the search for planets orbiting other stars) handle this one:
Wondering more about distant worlds? Read this Galactic FAQ.
Pop CulturePop Culture
The mysteries of our universe have long captivated science fiction authors and filmmakers.
Many scientists say they were inspired by the science fiction television series "Star Trek" – which first aired on television in 1966 and has been reinvented numerous times on both small and big screens in the decades since. The original show followed the crew of the starship Enterprise on a five-year mission to explore our galaxy.
Another inspiration – science fiction author Arthur C. Clarke’s "2001: A Space Odyssey" in which a fictional astronaut is transported across the cosmos through a mysterious portal. The next generation may be inspired by the 2014 movie "Interstellar" – where a fictional team of astronauts searches for a habitable planet around a black hole in a distant galaxy.
The 1980 television series "Cosmos" – which featured Voyager mission scientist Carl Sagan – took viewers on a factual tour of the known universe and sparked the imaginations of many present-day scientists and engineers. The series was reimagined in 2014 with astronomer Neil deGrasse Tyson as the host.
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