AstroFan: Galaxy Types!
Header Caption: This Hubble Deep Field image shows a snapshot of the diverse types of galaxies in our universe. Image Credit: NASA/JPL/STScI Hubble Deep Field Team
Did you know that up until the last century, humans believed that our Milky Way was the only galaxy in the known universe? Today, we now know that this couldn’t be further from reality.
In fact, it is currently estimated that there are two trillion galaxies in the known universe!
It’s no surprise that with such a large sample size, comes a diverse range of galaxies. Today we’re going to be doing a quick foray into the world of galaxy types!
But first…what is a galaxy?
To put it simply, galaxies are huge collections of gas, dust, and stars that are shaped and held together by gravity and dark matter.
The smallest of galaxies contain a “mere” few hundred million stars while the largest galaxies contain up to one hundred trillion stars!
Scientists have been able to segment galaxies into 4 main types: spiral, elliptical, peculiar, and irregular. Now, let’s dive in!
Types of Galaxies
Image Credit: X-ray: NASA/CXC/Wesleyan Univ./R.Kilgard, et al; Optical: NASA/STScI
The first type of galaxies—spiral galaxies—can be recognized by their wide, flat disks of rotating gas and dust.
Some spirals have wide flung arms like the above image of M51, while others have spirals that are more tightly bound.
Fun fact: our very own Milky Way is a spiral galaxy, and it is rotating at 168 miles per second. Now that’s fast!
Image Credit: NASA/ESA/STScI/M
Elliptical galaxies are given their name because of their oblong shape and lack of overall structure. Some are nearly spherical, while others are shaped more like a cigar. They can range in size from just a few light years across to being larger than our Milky Way.
Another fun fact: while it is not entirely clear how they form, some scientists propose that elliptical galaxies form as the result of galactic collisions!
Image Credit: Hubble Legacy Archive, NASA, ESA
Speaking of galactic collisions, peculiar galaxies are almost always the result of one!
Galactic collisions aren’t as action packed as you might imagine.
Since galaxies are mostly comprised of empty space, it’s unlikely that any two given stars will collide during the event of a galactic collision.
It is believed that peculiar galaxies compose 5 to 10 percent of all known galaxies. So, it’s safe to say that galactic collisions are a common occurrence in our own universe!
Image Credit: NASA
Irregular galaxies are galaxies that don’t fall under any of the three galaxy types mentioned above. These galaxies tend to be small, dwarf galaxies that lack any distinguishable shape. Many of these galaxies are companions or satellites to larger galaxies.
A final fun fact: The Milky Way has dozens of irregular satellite galaxies. Arguably the most famous one is the Large Magellanic Cloud, shown above.
Discover and Type Galaxies
Now that you’ve become a galaxy aficionado, why not put your knowledge to the test!?
With Galaxy Zoo by Zooniverse, you can help scientists discover and type hundreds of different galaxies.
Zooniverse—the world’s largest platform for people-powered research—is a collaboration between Chicago’s Adler Planetarium, the University of Oxford, the University of Minnesota, 1.9M+ participants, and hundreds of researchers around the world.
The next time you visit the Adler, make sure to check out our Galaxy Zoo touch table experience located in our Solar System exhibition.
So far, Adler guests have contributed to almost 140,000 galaxy classifications through the touch table alone!
Typing galaxies is a simple process that allows for even the most novice of AstroFans to partake in scientific discovery.
Give it a try! Who knows, you might even spot a few galactic collisions along the way…
Stay tuned for more awesome space facts on the next AstroFan.
Thank you for reading!
—Bianca, a.k.a. AstroFan