Looking back with "50 Years of Brown Dwarfs"

Posted by Sarah Scoles
on Wednesday, December 03, 2014

“Face it,” says the sunglasses-sporting protagonist of a 1996 New Yorker cartoon. “In this town, you’re either a star or you’re just another brown dwarf.”

While science jokes fill modern-day Facebook feeds (“What do you do with an old chemist? … Barium”), this one still holds its own. It doesn’t rely on punny-ness but, instead, explains what a brown dwarf is: an object that failed to become a bright-burning star.

But that’s a pretty simplified definition, and it only conveys what a brown dwarf isn’t, not what it is. You wouldn’t like it if someone described you as that not-tall, not-dark, not-handsome person. You’d prefer to be described as a normal-height, olive-skinned, “interesting”-looking person. Brown dwarfs, too, deserve to have their attributes affirmed.

That’s the idea behind a new book called 50 Years of Brown Dwarfs (Springer, 2014), edited by Viki Joergens. Through eight articles and essays, written by the scientists mired in the middle of the discoveries, the book explores the past half-century of brown-dwarf research. We rarely see the whole scientific process —complete with its delays, missteps, and methodological innovations — laid out before us. And we rarely hear it from the mouths of those who were sitting in the telescope control room or hunched over equation-filled notebooks. 50 Years of Brown Dwarfs provides that perspective, with the added value of those telescope controllers’ and equation writers’ hindsight.

“There are many examples in astronomy of the discovery of astronomical objects no one has anticipated to exist,” Joergens writes in the introductory article. “These discoveries are then often followed by long-lasting attempts to explain their existence theoretically.” The opposite, she continues, was true for brown dwarfs. Shiv S. Kumar first theorized their existence in the early 1960s, but more than 30 years would pass before anyone could point to a spot in space and say, “There is a brown dwarf, for sure.”

Kumar’s strange ideas about these supposed substellar objects more massive than planets but not big enough to sustain hydrogen fusion — meaning they glow mostly because of their temperature but then cool and dim to near-darkness — were mirrored by others. Chushiro Hayashi and Takenori Nakano, who composed the second article in the collection, calculated the minimum mass that a normal star needs to maintain hydrogen fusion a few years after the initial theory emerged.

With concrete calculations and predictions such as this, the theoretical idea of brown dwarfs became part of standard astronomy. But the objects didn’t have a name. They’d been called “black dwarfs,” “red dwarfs,” “infrared dwarfs,” and “failed stars.” But Jill Tarter, author of the third article, didn’t like those monikers. In 1975, she was a graduate student interested in whether these in-between objects could account for the “missing mass” in the universe. She referred to them with the term brown dwarf — a color “between” red and black — in the title of a chapter of her Ph.D. thesis: “Brown Dwarf Stars and How They Grow Old.” Tarter's contribution to this book is compellingly written, telling the personal and professional story of how the name came to be and why the symbolism of names is important. (The “missing matter” she researched would later come to be known as “dark matter,” although that was not Tarter’s doing.)

It would still be 20 more years before scientists found an actual brown dwarf in space. A couple of candidates came close, but no one could prove they fit the criteria. Then, in 1995, a bolt from the black: A group led by Rafael Rebolo discovered an object called Teide 1. The long search to prove the existence of brown dwarfs was over. But the effort to mine knowledge from physical observations was just beginning. Rebolo describes his team’s work, including archival pictures and handwritten notebook pages.

Two other teams, one of which Gibor Basri writes about in the next article, also found brown dwarfs in 1995. With physical objects found, astronomers then could estimate the total number of brown dwarfs in the galaxy (hint: a lot). And, just as the 5-minute-mile barrier stopped being a barrier as soon as one person broke it, these first discoveries ushered in a slew of subsequent ones. Brown dwarfs were now a field of observational study, warranting new spectral classes (described in Michael Cushing’s article) and a remodeling of our view of what’s out there.

There was a great deal of such view-remodeling going on in 1995, which was a special year for substellar objects of multiple sorts: Scientists also discovered the first planet orbiting a regular star (one that wasn’t the Sun). Ben R. Oppenheimer’s article reflects on the benefits and challenges of studying the “companions of stars.” “An exciting and perhaps even more profound set of contributions to science is within reach in the near future,” he says. “This includes an exploration of the diversity of planets in the universe and perhaps soon the first solid evidence for biological activity outside our solar system.”

This forward-looking prediction segues nicely into the last article, by Isabelle Baraffe, which looks at today’s study of brown dwarfs. Studies have moved beyond simply cataloging them and now probe their internal dynamics, magnetic fields, and the very dust in their atmospheres.

If you want to read astronomers' reflections on the process of science and see how knowledge accumulates (and twists and turns) across generations, 50 Years of Brown Dwarfs is a good book to pick up. It’s not beach reading, though, so you’ll need to put on your thinking cap before you open the cover. The volume is textbook-priced, and there’s (gasp) some math involved, but 50 Years of Brown Dwarfs would be a solid addition to a science-lover’s library, and the authors strive to describe the equations in words and let you follow their steps. They show their work, in more ways than one.

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