Galaxies: An Interview with Author Or Graur

Or Graur. Credit: Chris Pattison. 

We are excited to welcome back author Or Graur to the blog! Graur is an Associate Professor of Astrophysics at the University of Portsmouth's Institute of Cosmology and Gravitation, as well as a Research Associate at the American Museum of Natural History. On August 6, 2024, MIT Press published his book Galaxies, which is a concise but fascinating look at the history and present state of humanity’s understanding of galaxies. For more about Graur and his work, check out our 2022 interview with him about his other book from MIT Press, Supernova. 

Corinne Mona (CM): What was your impetus for writing this book? There is a fun introduction about the “galaxies” around us all the time (Milky Way bars, Guardians of the Galaxy, Hitchhiker’s Guide to the Galaxy…)  

Or Graur (OG): After writing a book about supernovae, I wanted to go bigger. There are plenty of books about the Universe and cosmology, but I was shocked to discover there were very few books about galaxies. I also thought this was one area of astrophysics that would hold a lot of surprises for readers. Most people know of galaxies from the beautiful images taken by the Hubble Space Telescope. In most cases, those images showcase spiral galaxies and, here and there, some exotic mergers. But what about ellipticals, lenticulars, dwarfs, and irregulars? I wanted to show that galaxies are far more than what is usually known about them, that they are fascinating island universes where most of astrophysics takes place. 

Hickson Compact Group 40 (HCG 40) This image from the Hubble Space Telescope features an unusual close-knit collection of five galaxies, called The Hickson Compact Group 40, including three spiral-shaped galaxies, an elliptical galaxy, and a lenticular (lens-like) galaxy. Credit: Credit: NASA, ESA, STScI, Alyssa Pagan (STScI). Text adapted from Hubblesite.org 

CM: Did your work on Supernova influence this book on galaxies? 

Cover of Galaxies. Credit: The MIT Press

OG: Definitely. Supernova was my first foray into popular science writing, and it provided a template for the structure I used for Galaxies. As in Supernova, I knew I wanted to talk about the classification of galaxies, their physics, and how galaxies are used as tools for other experiments in astrophysics. But I also wanted to grow beyond that template; I wanted to construct a narrative that would propel the reader from one chapter to the next. I found that narrative in the complex story of how galaxies formed and evolved over time. This story required the chapter structure I finally settled on, with chapters on classification, dark matter, and dark energy laying the ground for the chapter where I describe how galaxies formed in dark matter halos and went on to evolve into the zoo of galaxy types we see today. 

CM: I enjoyed the chapter about the etymology for the Milky Way and how it’s been described in various cultures. Why write about the origin of words in a book about science? 

OG: The words we use to describe scientific phenomena are shaped by culture and history, which automatically brings up the questions, “Whose culture? Whose history?” In too many popular science books, the implicit answers to these questions are “Western culture and European history.” That fails to capture the true and far richer global history of astronomy; it obscures the fact that we are all descended from ancient astronomers. That’s why I didn’t stop after recounting the Greek myth behind the English name for the Milky Way but dug deeper to introduce readers to other names, other cultures. I ended up falling down a deep rabbit hole, collecting more names and origin stories than I could fit into this book. This has now blossomed into a full-blown research project [first paper available here], where I collect and analyze the multicultural mythology of the Milky Way. What hooked me was the realization that cultures around the world and throughout history have again and again reached for the same motifs to conceptualize what they saw in the night sky, hinting at a shared underlying imagination that is not culture-dependent but deeply, simply human. 

CM: Throughout the book, you encourage the reader to relate themselves to the study of galaxies. I conducted the stellar parallax technique on my cat as I read the book (though he was happily eating a snack, not glaring at me, as suggested in the book). The last chapter of the book deals with ways that laypeople can get involved with galaxies. Why is this important? 

OG: It’s important because for too many years, academia has been described as an ivory tower, a realm of closed-off elite universities where stodgy, socially inept, half-mad geniuses come up with theories that no “normal” person could ever fully comprehend. This stereotype turns people off and turns them away; it makes too many people think that they could never be scientists, which means they never try. The reality is that we’re not like that at all, but it’s very, very hard to fight against this pernicious stereotype. Luckily, we live in a time when science is more accessible than ever before. Anyone can now take part in real experiments, no matter where they are, how old they are, or whether or not they know any physics or math. Citizen science, which allows people to participate in science projects from their computers, tablets, even their phones, is a revolution in the way science is done. Yet it’s barely reported on. I want more people to know about this revolution and invite them to join it. [Editor’s note: Graur encourages readers to check out Galaxy Zoo, one of the longest-running citizen science galaxy projects, and Zooniverse, which has many more projects to get involved with!] 

Hoag’s Object is a stunning example of a ring galaxy, a temporary phenomenon often caused by a second galaxy passing through the first and disturbing the stars’ orbits. Look closely, and you’ll see a second, redder ring galaxy behind Hoag’s Object. Credit: NASA, R. Lucas (STScI/AURA). 

CM: Reading about the vastness of space and the future collision of the Milky Way and Andromeda galaxies can make one feel very small. More than other fields, astronomy has a way of reminding us that humanity’s existence and our very own planet are not permanent. How do you grapple with the existential dread? 

OG: Astrophysics has never been a source of existential dread for me (there are plenty of other sources for that nasty feeling). On the contrary, as I note several times in the book, I’m filled with a sense of wonder, not just at the beauty and complexity of galaxies, supernovae, and black holes, but at the fact that we, tiny little carbon-based semi-intelligent life forms, are able to gaze up at the stars and make sense of what we see, not just in the night sky but all the way across the Universe. As I put it in the book: “What is heroic is the scientific endeavor itself, the continuous attempt by a short-lived, short-tempered species of ape to overcome mere instinct and strive to make sense of itself and the world around it through the application of thought and reason.” That doesn’t make me feel existential dread; it makes me proud of what we’ve been able to figure out so far, and fills me with hope for what we’ll manage to figure out in the future. 

Siblings Caroline and William Herschel were an unusual but highly influential pair of 18th century musicians-turned-astronomers. The book talks about their story in the context of humanity’s continually evolving understanding of galaxies throughout history. Here, Caroline is depicted taking notes as her brother William Herschel observes the sky and discovers Uranus on March 13, 1781. Credit: Paul Fouché. Public domain. 

CM: What libraries and archives did you find useful while doing research for the book? 

OG: Astrophysicists are privileged to have the wonderful SAO Astrophysics Data System (ADS for short), which is a database of all of the papers published in astrophysics. This database is updated on a daily basis, and is constantly scanning historical papers in as well. Almost every paper in astrophysics you can think of is in this database. For books, I rely on other sources. Archive.org [the Internet Archive] is excellent, especially for books that are no longer under copyright. For everything else, I use the research libraries at the University of Cambridge and the American Museum of Natural History.  

CM: Please tell us about the planet Vulcan and its relation to dark matter. 

Vulcans from planet Vulcan: Arlene Martel in the role of T'Pring and Leonard Nimoy as Spock. 1967. Credit: NBC Television. Public domain. 

OG: Vulcan is, of course, Mr. Spock’s home planet and one of the three founding members of the United Federation of Planets (along with Earth and Andoria). But before Star Trek came along, it was thought to be a planet hiding somewhere between Mercury and the Sun. In the nineteenth century, astronomers and mathematicians finally had the tools to precisely chart the orbits of the then-known planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Uranus). They also had the theoretical tools to calculate what those orbits should be based on Newton’s laws of gravity and Kepler’s laws of motion. But the theoretical calculations didn’t match the observations. The deviations hinted that there were missing sources of mass in the Solar System, and everyone assumed that meant there were at least two more planets that had never been seen before: one somewhere between Mercury and the Sun and the other beyond the orbit of Saturn. The latter planet, Neptune, was discovered pretty quickly, exactly where it was predicted to be. But Vulcan was never discovered. It was only in the mid twentieth century, when Albert Einstein published his theory of general relativity, that astronomers realized that Vulcan never existed to begin with (sorry, Spock). While Neptune was indeed a case of missing mass, Vulcan was a result of astronomers using an incorrect mathematical model (Newtonian dynamics) to explain nature. We needed a brand-new way of comprehending the Universe – general relativity – to explain Mercury’s orbit around the Sun. We can think of this as a parable for our current search for the nature of dark matter: it could be that we’re missing some type of mass that we haven’t been able to detect before. But it could also be a hint that there’s something fundamentally wrong with our current physics and that we need a new way to comprehend the world around us. 

CM: What is your favorite galaxy? 

OG: Right now, it’s the Milky Way. Even though we live in it, and can see most of it in the night sky without a telescope (every star in the night sky is part of the Milky Way), it’s still full of surprises (Fermi bubbles, for example). It’s also played a role in the astronomies and cosmologies of nearly every culture across the world, which truly makes it our galaxy. 

CM: You’re an astrophysicist. How do you approach writing about your subject for a non-specialist audience? 

OG: I imagine how I would explain a topic to my family and friends, or to a complete stranger at a public event. I love giving public talks, and I’ve tried to copy the way I speak at these events into my popular science writing. 

CM: What questions do you hope that readers will ask after they’ve read the book? 

OG: What else is there to know about galaxies (lots; I’ve only covered the essentials)? How can I become an astrophysicist (check out https://aas.org/careers/career-in-astronomy)? Can I study with you (check out https://www.port.ac.uk/research/institute-of-cosmology-and-gravitation)?  

Portrait of Vesto Melvin Slipher. Credit: AIP Emilio Segrè Visual Archives, Catalog ID: Slipher Vesto Melvin A1

CM: What was the most interesting thing you learned while writing Galaxies? 

OG: That we owe the discovery that the Universe is expanding to an astronomer I had never heard of. As I describe in Chapter 5, V. M. Slipher’s spectroscopic measurements of galaxy redshifts were the observations that got theorists thinking that maybe the Universe wasn’t static after all, that maybe we were living in a dynamic Universe that could expand and contract. Several observers then tried to combine Slipher’s redshifts with estimates of distances to his galaxies to test those theories. The most famous of these attempts was made by Edwin Hubble, who today is singlehandedly credited with discovering the expansion of the Universe. Tragically, Slipher has been all but forgotten, even though without him, who knows when we would have discovered that the Universe was expanding. I hope Galaxies will help bring Slipher’s achievements to the fore once more. 

CM: Is there anything else you wish I’d asked about Galaxies? 

OG: Why is it dedicated to your parents? Because more than anyone else, they taught me how to ask questions, seek answers on my own, and think critically. Without those skills, I could never have become a scientist.