The farthest astronomical object observable with the naked eye in our night sky is the Andromeda Galaxy. At 2.537 million light years distance, it’s pretty close, by universe standards, especially when you consider the farthest known galaxy is 13.8 billion light years away. A light year is the distance it takes light to travel in an Earth year.
The Andromeda Galaxy is a typical clockwise spiral galaxy with a dominant central bulge but no central bar. Compared to our Milky Way Galaxy, Andromeda is quite a bit larger — 220,000 light years across compared to Milky Way at 100,000 and containing 1 trillion stars compared to Milky Way containing 200 to 400 billion stars. Milky Way has a dominant central bulge, but it has a central bar. Notably, while the rest of the universe of galaxies are moving away from us, Andromeda Galaxy is moving toward us, more-local gravitational attraction having a greater effect than does the expansion of space-time.
There are billions to trillions of other galaxies to observe in the universe, most of them by various kinds of telescopes. What we now know about them has changed a lot recently. I got a good look at that when I participated in citizen science through the Galaxy Zoo project beginning in 2007. Its first project was categorizing galaxies by type: elliptical or spiral and how many arms the spirals have. Then whether spirals were clockwise or counterclockwise — yes, there are counterclockwise spiral galaxies! We also studied galaxy mergers and explored the colors of ellipticals and the sizes of spiral central bulges and bars and whether the spirals were symmetrical. Then we peared into the early cosmos and looked at galaxy clumping for signs of the earliest galaxy formations. More recently, we have looked for signs that galaxies spin around their bars.
One of the more startling discoveries through the Galaxy Zoo project was the Green Pea galaxy, which occurred in 2009. They have unusual amounts of doubly ionized oxygen atoms and they form stars 10 times the rate of the Milky Way, despite being 10 times smaller and 100 times less massive.
The same citizen scientist who discovered the Green Peas also discovered another mystery associated with galaxies called Hanny’s Voorwerp, Dutch for “Hanny’s Object”. This 24 year old school teacher was looking at galaxy images in the Galaxy Zoo project in 2007 when she saw a mysterious blue object near a spiral galaxy that no one could explain. It now turns out to be associated with an active galactic nucleus (AGN) not previously associated with that galaxy and the subsequent discovery that AGN’s can switch off occasionally.
Some other things discovered include the distribution of dust lanes and its relationship to the age of galaxies, the relationship of galaxy color to age and the relationship of color to star formation, the idea that ellipticals may be older merged spiral galaxies, and the variations in color of elliptical galaxies.
Finally, we used Hubble and other images in the Galaxy Zoo project to look for gravitational lensing to help identify galaxies magnified behind other galaxies, which aided exploration of deeper field and even older galaxies, galaxies on the edge of the observable universe.
When I was a teen and in my early 20’s, we didn’t really know a lot about galaxies. There were several known categories of spirals and ellipticals and that was about it. But now, it seems every few months there are amazing new discoveries announced. And new projects open up in the Galaxy Zoo project to help astronomers and cosmologists comb through images and data to discover new insights on some of the most beautiful sights in the cosmos that are the collections of stars and other objects we know as galaxies. This really is an amazing time in the space sciences.
© 2017. Alan Eggleston. All Rights Reserved.