Sociologist and bestselling author Sarah Thornton with a droopy work by Brazilian artist Ernesto Neto at the Hirshhorn Museum and Sculpture Garden. (Linda Davidson/The Washington Post)

Sarah Thornton is in a Hirshhorn gallery, lingering beneath a piece by the Brazilian artist Ernesto Neto. It’s a massive, bulbous, inexplicably sexual thing that droops down from the ceiling and fills the whole space.

“Does it still smell?” Thornton wants to know.

A young staff member looks confused. It doesn’t. It never did, he says.

Neto, Thornton explains, often fills his saggy sculptures with spices such as turmeric, cumin and cloves. The Hirshhorn’s is more like an innocuous bean bag, filled with tiny foam pellets, and Thornton, though she has written two books about contemporary art, has never seen one quite like it.

Perhaps that’s why she breaks the cardinal rule of the museum world — never touch the art — and stretches out her hand to inspect the piece more closely, sending several nervous staff members lunging in her direction.

Thornton might be forgiven her faux pas. For the past several years, the sociologist and best-selling author — a breezy presence in a stylishly skinny black pantsuit and comically towering Stella McCartney platforms — has been nosing around the prop drawers of conceptual photographer Cindy Sherman and crunching around on Chinese contemporary art star Ai Weiwei’s “Sunflower Seeds.” She has been talked to death by Jeff Koons. And she has sniffed her fair share of Netos.

At 49, Thornton is the Jane Goodall of the art world. An academic, she has probed and prodded her way to one of the best views of the high-stakes international art market, and into the studios of the occasionally ego-driven, market-conscious artists whose works regularly fetch upward of $50 million apiece.

It’s an exclusive, insular world, but Thornton’s first book about art, 2008’s “Seven Days in the Art World,” was pure populism, a dishy, behind-the-scenes read about heady auctions at Christie’s, the cutthroat atmosphere of art fairs, and much more. It became an unexpected bestseller and landed the writer in art’s inner circle.

“For the longest time, nobody wanted to publish it,” Thornton recalls. “I kept hearing, ‘Nobody wants to read about the art world, and art books don’t sell.’ ”

But “people,” she says, “are interested in people.”

The artists Thornton follows are people, and then some. They have personas. “There are these compelling characters,” Thornton says, “who carry along with them lots of ideas and insights.”

Last week, Thornton was poking around the Hirshhorn in the hours before she would be the guest of honor at a discussion of her new book, “33 Artists in 3 Acts,” which chronicles her nearly five-year quest to understand what makes artists tick.

Our quest, right now, is to understand this: Why do artists let her burrow through their crannies — literal and metaphorical — in the first place?

An outsider insider

Thornton has the ability to “seduce people to expose themselves,” the artist Andrea Fraser recently told an audience at New York’s New Museum.

The author’s two volumes on art read nothing like most art books, which are often academic tomes or picture-filled coffee-table books. But “33 Artists” has just one muddy black-and-white image for every chapter. Instead, Thornton fills in the blanks, writing so evocatively that the reader can easily imagine the immensity of a hundred million sunflower seeds rendered in porcelain by Ai.

This has won her a readership that extends beyond contemporary art’s usual players, and for artists who work with Thornton, Fraser explained, “part of the seduction is the potential to reach that kind of audience.”

Fraser and others opened their doors to Thornton as she traversed the globe to interview and observe artists in their own world. The author watches as Maurizio Cattelan prepares for what he called his retirement retrospective at New York’s Guggenheim in 2011. She is with eccentric Japanese pop artist Yayoi Kusama on the eve of her phenomenal 2012 comeback, when she landed a retrospective at the Whitney and a complementary Louis Vuitton line. And Thornton spends time in the studios of photographer Laurie Simmons and her husband, painter Carroll Dunham, just before their daughter, Lena, lands a deal with HBO.

This is one of Thornton’s greatest knacks: She tends to arrive on artists’ doorsteps just before some seismic shift in their public profiles. But her other talent is gaining access, penetrating artists’ private spheres as both an art-world insider and an academically minded outsider.

Not that they all say yes. “Oftentimes, an artist won’t want to see me, but then they give in,” Thornton says with a chuckle. Sherman was one who at first rebuffed her, says Thornton, and then became “incredibly generous” with her time.

Her subjects say that being an academic is part of her appeal. “Thank God she’s not part of the establishment,” says Massimiliano Gioni, artistic director of the New Museum and the focus of a chapter in “33 Artists.” “She’s not assimilated, and that gives her the perspective and the distance to look at things with complexity.”

On the periphery

Raised in Montreal, Thornton has been looking at art practically her whole life. Her mother, Glenda, was a longtime docent (she still volunteers at Atlanta’s High Museum of Art), and Thornton spent much of her childhood roaming museums. As an art history major at Concordia University in Montreal, she got a healthy dose of contemporary art. But for her doctorate, she chose sociology. It still informs her research methods.

“She was kind of a ghost,” Mika Yoshitake recalls of her first brush with Thornton in 2007, when the writer was researching “Seven Days.” Thornton had traveled to Japan to witness the manic experience of putting together Takashi Murakami’s huge exhibition for Los Angeles’s Museum of Contemporary Art. Yoshitake, now an assistant curator at the Hirshhorn, was working with the museum on the retrospective, and she recalls Thornton as an almost entirely silent observer.

Ask how it feels to have been the subject of Thornton’s occasionally cutting gaze, and you can almost hear a slight shudder in Yoshitake’s voice. “It was kind of amusing,” she says with a laugh. When tensions between the museum and the artist nearly came to a head over the placement of a garish 19-foot, platinum-covered Buddha, Yoshitake recalls, “I was so in it, I don’t remember what happened. But [Thornton] — kind of blow-by-blow — was able to explain it, and it was so fascinating.”

It helps to remain on the periphery. Thornton has long lived far from the art hotbeds, residing for the past 20 years mostly in London, which has what she describes as a fairly “cliquey” art scene. (She has never lived in New York.) She is gay, which, she says, “makes you an outsider sometimes.” And she is a mother, to 16-year-old Cora and 18-year-old Otto, which sets her apart, she acknowledges, from many of the female artists she has observed.

Yet it’s clear, as she flits across the Hirshhorn murmuring her thoughts on each piece, from the Andy Warhol to the Bruce Nauman, that the art world is as much her place as it is the artists’. Writing has simply given her a way to interact with them.

In one scene in “Seven Days,” a Sotheby’s employee tells Thornton, “We don’t deal with artists, just the work, and it’s a good thing, too.”

Was this some kind of warning, that artists’ egos and personalities would be hard to capture in her new book?

“I don’t think artists are any more difficult to interview than dealers,” Thornton replies. “In fact, dealers are more difficult. They’re more likely to give you PR than artists are.

“The good thing about artists,” she adds, “is they have a belief in the truth.”