Galaxies are bound by gravity and made up of stars, remnants of stars, interstellar dust and gas, and the not yet completely explained “dark matter.”
Galaxy sizes can be smaller, ranging with ten million stars all the way to huge giants that have a hundred trillion stars. A majority of the galaxies that we know of are the smaller dwarf galaxies.
Each star has an orbit within its galaxy and scientists estimate that there may be more than 170 billion galaxies in the universe we have observed so far.
There may be more galaxies but their light is so dim that we might never be able to see them.
The Milky Way
The idea of galaxies was once just a theory. Immanuel Kant, an 18th century philosopher, was one of the first people to think that the Milky Way was just one of many galaxies in the universe.
He created the term “island universe” as a galaxy description.
The study of galaxies has given us the ability to recognize that they come in three main types by shape: spirals, ellipticals, and irregulars. Each type also has additional subtypes that are recognized by specific characteristics.
The word “galaxy” comes from the Greek word “galaxias” which means “milky,” and was used to describe our own Milky Way galaxy that contains our Solar System.
Although many years have been devoted to cataloging over tens of thousands of galaxies, only a few galaxies have been given names such as the Milky Way, Andromeda, Sombrero, Whirlpool and the Magellanic clouds.
The three types of galaxies by shape are described as:
- Spiral: disk-shaped, usually have long curving arms.
- Elliptical: elongated and oval-shaped light profile.
- Irregular: Have a shape outside of the other two types and is often more unusual or unique.
Galaxies are measured in “parsecs.” One parsec is equal to around 19 trillion miles (31 trillion kilometers).
A majority of the galaxies that we know of have a diameter measurement of between 1,000 and 10,000 parsecs. Scientists know that the universe is expanding and this causes galaxies to recede from each other.
The distances between galaxies gets bigger and bigger, and we have found that the farther away a galaxy is from the Milky Way, the faster the speed.
Facts about Galaxies
- It’s believed that every galaxy has a black hole at its center. The comparative size relation of the black hole to the size of its host galaxy is around 1/1000th of the size. Some scientists think that black holes play an important role in the formation of galaxies.
- So far, the most distant and oldest galaxy that we have discovered is the z8 GND 5296 galaxy. It’s around 13.1 billion light years away and was discovered by a team of astronomers in 2013 from the University of Texas at Austin; with the leader Steven Finkelstein.
- One of the mysteries of galaxies is that many of the dwarf galaxies often cluster around galaxies of larger sizes. The intense gravitational pull of the larger galaxies cause the loss of stars from the dwarf galaxies as their stars are stolen. The position also causes the destruction of many of the dwarf galaxies.
- All galaxies contain dust that is produced by their stars. The dust is what makes the galaxies have a redder appearance than they truly have. This is one of the challenges that astronomers have in viewing galaxies.
- Some galaxies have galactic winds that expel the gases and dust into the spaces between each galaxy, known as the intergalactic medium, at hundreds of km per second.
- Galactic wind is caused when the energy from the starlight exerts pressure on the gas and dust in the galaxy. The fastest speeds of the galactic winds seem to be in faraway galaxies that are forming stars.
- Our Milky Way galaxy has a rotation speed of nearing 250 km/second (560,000 mph). It takes 200 million years to complete a full revolution.
- What are the three types of galaxies?
Spiral, Elliptical, and Irregular
- A majority of the known galaxies are of the smaller variety. What are they called?
- Have all known galaxies been named?
noonly a few
- What makes the dust in galaxies more difficult for astronomers?
causes a reddish color
- How fast is the Milky Way galaxy rotating?
250 km/second (560,000 mph)
- How many years does it take the Milky Way to make a full revolution?
200 million years