Beth Willman Really Does Have A Galaxy

She does. Actually, it’s not much of a galaxy, it’s more of a sub-galaxy, a dwarf galaxy, or maybe not even any kind of galaxy at all, maybe just a cluster of stars. It’s hers because she found it, hanging around the edges of the Milky Way. That’s it, above. If you look with the eye of love, you can see in the left-middle what she calls a “slight overdensity” of dim blue stars. It’s named Willman 1.

Beth Willman is now a member of the astronomy faculty at Haverford College. When she found Willman 1, though, she was a postdoc at NYU (astronomers have long childhoods that don’t end with a doctoral degree) and not particularly interested in galaxies. She was interested in cold dark matter, invisible stuff with no other name, smallish clumps of which were predicted to exist nearby in the tens of thousands, and of which astronomers had found only tens. So she was looking, she said, “for the nothing that was there” and so far she hadn’t been seeing it; in fact her doctoral dissertation was about her non-detection of nothing.

You find this nothing, this clump of cold dark matter, because it’s full of shining little tracer particles, sprinklings of regular matter that have turned into stars. So now as a postdoc and in spite of not caring about galaxies, she was looking, she said “for galaxies that might have been detected if they’d been there.” She’d log in to the enormous database gathered by the Sloan Digital Sky Survey—astronomy these days is rarely done with a telescope—and get back lists of numbers corresponding to the positions, colors, and brightnesses of millions of stars.

Then she’d also ask the database for actual images. In one of them, she thought she saw some small blue overdensity. So did a colleague, Mike Blanton. In the next office was a particle physicist named Neal, so they called him over and said, “Neal, do you see anything here?” and Neal pointed to the overdensity and said, “That something there?” If even a particle physicist could see it, Beth Willman thought, it must be there. Then she thought, “Now I’ve got to go to a telescope.”

As it happened, she didn’t. Telescopes take effort: you apply for time far in advance that you might or might not get; you leave home and live on some mountain for however long it takes; you sleep all day, work all night; if the weather’s bad, that’s it, you’re out; and astronomers love it. Instead a colleague had time at the Apache Point Observatory’s 3.5 meter and got a deeper image showing more stars, meaning that the overdensity was real. She published a paper called “A New Milky Way Companion.”

Officially it was called SDSS-1049+5103, the numbers being its position on the sky in right ascension and declination, plus the survey name—a naming protocol that even astronomers feel is lame. Luckily again, a more experienced NYU astronomer named David Hogg advised her that the press release would look better if her overdensity were named Willman 1 and also her parents would like it. Then other colleagues picked up the name and it stuck.

She didn’t know exactly what Willman 1 was, whether it was a star cluster or a dwarf galaxy, and she still doesn’t but she’s pretty sure it’s a dwarf. It’s about 75 light years across, 100,000 light years away. “It looks like the Milky Way is disturbing it,” she says. “It’s moving away but not very fast,” meaning it’s feeling the Milky Way’s gravitational field and it will get just so far before it turns and boomerangs back. In the image above—”NOT a great image,” she says, “but it does show reality”—the “streaky crud” is two satellites, the big red halo things are bright stars, most of the rest of the tiny points are stars, and the soft small blue halo things are whole galaxies. Willman 1 was the faintest dwarf anyone had seen, by orders of magnitude. That was in 2005, and asked to put money on it, she would have said it was just something weird.

But then she found another ultrafaint dwarf, called Ursa Major 1, and a colleague found another one called Bootes 2, and other people found still other ones; and around the corner at the end of this decade is a splendidly gigantic new sky survey that should hold many, many more; and now Beth Willman and her colleagues wonder whether they’ve seen only the tip, whether—all the majestic giant spirals and ellipticals aside—these little dwarfs are the universe’s most numerous galaxies. And the astronomers don’t want a yes or no answer, they want to know how galaxies form in their nests of dark matter, and what sizes dark matter clumps come in and how they’re distributed throughout the universe. “Over the next decade,” she says, “we’re going to learn a lot about something.”

Beth Willman says that she and Wil 1 have a love-hate relationship. Willman 1 gave her “great name recognition,” she says, and in this cut-throat field, helped her get the Haverford job. And she loves the nearly-invisible, modest ultrafaint dwarf, so small and hopeful. She loves its little number of brothers, she loves that other Wil 1’s are out there, she loves that the universe holds “such unusual and puzzling things.”

But Wil 1 is frustrating. Colleagues who didn’t know the history scolded her for naming it after herself. And like most scientists, she takes care with certainty: though she thinks it’s a dwarf, she’s cautious about calling it one; nor is she 100 percent sure which stars belong to it and which to the Milky Way; and something about its spatial and velocity distribution is odd. In spite of not knowing everything she wants to know about it, she says, “it also feels weird studying an object named after me, so I have no intention of writing a paper about this object again.” But if astronomers understand anything about the universe, it’s that they can’t imagine the extent to which all the things they can’t imagine are possible, so she adds, “But who knows.”



Ann Finkbeiner is a proprietor of The Last Word on Nothing.