The Galaxy Garden at Paleaku Peace Gardens Sanctuary on the Big Island of Hawai’i. Image copyright 2013 Carolyn Collins Petersen.
Back when I was in college the first time (about the time of the Triassic), I had an astronomy professor who encouraged us to be creative in our final projects for extra credit. I was already running an A in the class, so I decided to do a book review of a popular “science” book that turned out to be about a hoax subject. Some of my other classmates were much more creative, and so they turned in things like a pizza in the shape of M51, quilted stars, and star poetry.
I was reminded of that class (and how much fun we had the last day eating that pizza and listening to a poetry reading) when I saw a little blurb online about the Galaxy Garden in Kona, Hawai’i. It’s an actual garden in the shape of our Milky Way Galaxy and each plant and flower has special significance to help explain the shape and makeup of our galaxy. There’s an amazing wealth of educational info on the website — I suggest you check out the page and its wonderful explanations of the art and design, as well as the science of the garden!
I happen to be a huge fan of the Big Island of Hawai’i. I did two planetary science field trips there during grad school, went on an eclipse expedition there in 1991, have been to several meetings there and in Honolulu, and I work with the folks at Gemini and Subaru Observatories from time to time with their public outreach materials.
I’m also a fan of Jon Lomberg’s work. He lives on the Big Island but his work is known world-wide. His art is featured in Cosmos(the ground-breaking TV documentary by Carl Sagan and Anne Druyan), and has been commissioned by NASA, the Soviet Academy of Sciences, Sky & Telescope Magazine, and on the covers of various magazines and books. He’s a great and creative guy and so it’s no surprise that he conceived of and implemented this lovely garden at the Paleaku Peace Gardens Sanctuary in Kona. It looks wonderful and I can’t wait to go back to the Big Island and see it!
We live in a region of the Milky Way Galaxy where our neighbors are pretty few and far between. The closest star is 4.5 light-years away and even if we had a good interstellar space ship that could travel at oh, say, a tenth the speed of light (roughly 300,000,000 meters per second), it would take centuries to get there. It would appear that living the galactic sticks is part and parcel of being in our spiral galaxy.
The large image shows a star field imaged by Dr. Michael Hilker, using the 2.5-meter Du Pont Telescope at Las Campanas, Chile. The inset boxes are close-ups made using HST of two ultra compact dwarf galaxies, courtesy Michael Drinkwater of the University of Queensland. (Click to exframulate.)
But, what if we lived in a galaxy that was perhaps 1/1000 the diameter of the Milky Way? Say something like an Ultra Compact Dwarf Galaxy? Such objects existed in the early universe and they had stars jam-packed together in a region only about 60 light-years across! The bright star Aldebaran in the constellation Taurus is around 60 light-years away. Imagine packing a whole galaxy into the space between us and Aldebaran!
So, does a galaxy’s size matter? It could, depending on what you want to know about it.
For one thing, if there were any planets around these stars (and that’s probably doubtful), the “light pollution” from all the nearby stars would drown out our view of the more distant ones. For another, these objects were most likely formed when more “normal” galaxies collided and mingled stars a few billion years after the Big Bang. That means that they’ve experienced some major transformations and evolution since then.
Actually, what really matters about these UCDs (as they are often referred to) is their masses. They seem to have way more matter than their starlight implies. Could they be full of massive stars or dark matter? Or something else?
A team of astronomers led by Professor Pavel Kroupa and graduate student Joerg Dabringhousen of the University of Bonn has been looking at UCDs to figure out what they’re made of. They think that each UCD was incredibly packed with stars — maybe as many as a million in each cubic light -year of space. For comparison, in our part of the Milky Way, that number is closer 1 star per cubic light-year. Think of cramming a million stars within a cubic light-year of the solar system. The sky would literally glow.
Having stars crammed together that closely in the UCDs means that over time, they could merge together to build hugely massive stars — the kind that live fast and die young as supernovae. What’s left of these massive stars at that point are superdense neutron stars or the occasional black hole. Both of which are incredibly dense without being bright.
So in today’s UCDs, much of their mass is sunk into these dark remnants that you can think of as fossils pointing the way to a more dramatic and active past. Billions of years ago they must have looked absolutely stunningly bright. And, if you were inside one, on a hypothethical planet, your sky would be nothing but stars making it as bright as a sunny day here on Earth.
