They’re as steady, stoic and unflappable as art gets — but emotion rises off the black-and-white photographs of Nicholas Nixon like steam. It’s impossible to contain. You feel it in the pores of your skin.

Nixon, a longtime resident of Boston, is best known for “The Brown Sisters.” Annually, since 1975, he has photographed his wife, Bebe, together with her three sisters, Mimi, Laurie and Heather. The settings change, but each year, the women appear in the same order.

Once so supple-skinned and fiery-eyed, these beautiful, unflinching women year-by-year grow wearier, perhaps wiser, certainly closer to their end. Part of the power of the series, which is now in its 44th year and has been shown all over the world, is that it forces a reckoning. The same process is happening to us all.

The conceit of the project — mortality marked off like tree rings — is so inherently engaging that it’s easy to miss how artful the photographs are.

That’s why I am so struck by a new display of the series at Boston’s Institute of Contemporary Art. The portraits of the sisters are shown chronologically in a horizontal line along the four walls of a large gallery. But hanging above and below each portrait of the sisters are two unrelated images, linked only by the fact that Nixon took them in the same year.

The effect is not just to remind us that Nixon’s achievement stretches far beyond the Brown sisters. It is, in human terms, to let more light in. A series that can seem intense and hermetic, cut off from the wider world, is gently cracked open, the world let back in.

Over the years, Nixon has spent months and often years on projects that have taken him out into the world and into the most intimate crannies of other people’s lives. He has photographed porch life in the rural South, students in Boston schools and people with AIDS. These searching, deeply compassionate projects have been complemented by cityscapes of bracing objectivity.

Setting single examples from Nixon’s other bodies of work against the entire and ongoing Brown sisters series sets up fascinating correspondences. Each photograph in each trio (occasionally it’s just a duo) complicates the others.

In one trio, from 1982, the cozy, consolidated femininity of the Brown sisters, all wearing winter gear, hangs above an anarchic, summer image of boys playing with toy guns. There is not a whiff of polemic in either picture (“The world is infinitely more interesting than any of my opinions about it,” Nixon has said.) But somehow, as you contemplate the two together — women, men; adults, children; order, chaos — it feels as though civilization itself might be at stake.

Hanging serenely above both is a portrait, from the same year, of a girl standing in front of a door. A boy, who looks like her brother, is seen, semi-obscured, through a transparent panel in the door. Aware of being on show, the girl looks neat and self-contained. Her smile is warm and open. The brother within, protected by darkness, looks out more intently and less self-consciously.

These subtle psychological dynamics are emphasized by formal contrasts — dark and light, curved and straight — and the image is unified by teasing half-rhymes: the repeating curves of the window frame, for instance, echo the silhouette of the girl’s cheek and the outline of the eagle icon on the door.

In another trio of images, this one from 1988, the Brown sisters, aglow with warm feelings, are sandwiched between two images of the same man. In the first, he wears a dressing gown and examines his face in a mirror. In the second, taken later that year, he is shown, emaciated and bedridden, being embraced by his parents.

The man, Bob Sappenfield, was an adviser on public policy and a doctoral candidate at Harvard’s Kennedy School of Government when, at the beginning of 1987, he was diagnosed with AIDS. Sappenfield quit his jobs and, even as his health was falling apart, dedicated himself to educating others about a disease he called “the great thief.”

His parents — Ginny, a nurse, and Robert, a doctor — came up from their home in New Orleans to care for him in the summer of the following year. Nixon’s book, “People With AIDS,” reproduces a letter Dr. Sappenfield wrote that fall. “Dear God,” it begins, “please bring comfort and peace to my son, Bob, who is in the terminal stages of AIDS.”

Words are redundant before an image of parents embracing their dying son.

But when contemplating what these three images from 1988 might have in common, it’s enough, perhaps, to observe that in all three there is a kind of doubling and redoubling, both of bodies and gazes. A sense of multiplication, which is the simple product of life loving itself.

Something analogous is at the heart of Nixon’s photographic project: He shows us to ourselves; reminds us of our common, mortal fate; and makes us contemplate what the sharing of that fate implies.