A friend describes her romantic aspirations this way — binary stars.

She wants to find someone whose orbit is their own, but revolves around the same epicenter as hers — #relationship goals.

My friend might not be asking for too much with her expectations. It is estimated that more than half of stars are binary stars, so they are more common than one might think.

Binary stars are gravitationally bound entities that have their own orbital path around a shared center mass. In their travels they also orbit each other. There can be two or more stars in this type of association.

In all relationships there are roles. For binary stars, the brighter one is the primary, also called star A, and the dimmer star is the secondary, or star B. If these bodies are of equal brightness the discoverer of the system gets to choose which is which.

And as with any partnership there are individual distinctions. Wide binaries are stars whose orbits spread far apart from each other and evolve separately with little impact or effect on their partners. Close binaries are near enough to transfer mass from one to the other, and the stronger one can even engulf the weaker.

Sometimes, one of the star partners isn’t observable. The unseen star is only known because of its gravitational force on its visible partner. It can also be hidden by virtue of being a black hole. The best known star with an invisible companion is Cygnus X-1.

Galileo Galilei was credited with finding the first binary star in 1617. He observed it after turning his telescope to the Big Dipper. At the end of its handle Galileo saw what he believed was two stars. In actuality, there were six stars in that cluster that were interacting. Sir William Herschel coined the term binary star later, in 1802.

These binary star couples are believed to be formed when a mass of gas and dust that is in the process of collapsing on itself to form a star divides into two parts, or when gas and dust orbiting around a single star forms a new star in the original’s orbit. In rare cases, one star can capture another already-created star and draw it into its orbit.

Binary stars can be visual, spectroscopic, eclipsing or astrometric. Visual binaries have wide enough separations that both can be viewed, while spectroscopic couples appear so close that their distance can only be determined based on wavelengths of their light emitted. The eclipsing variety has its pairs at such an angle that one passes in front of each other in a horizontal line of observation. Astrometric duos are pairs where only one of the two stars is visible to us because it seems to dance around empty space. The existence of its companion star can be inferred due to the influence of its gravity, causing the visible star to wobble.

Though binary stars are sometimes called double stars, not all double stars are binary groups. Double stars define two stars that are seen together or appear close, but not all of them have the gravitation requirements of binary stars.

No matter what you call them, their activities in the heavens inspire comparisons to earthly couples. As for my friend, there is no fault in her stars for her desire for a twinkling relationship. Because at the place where romance and science meet, the possibilities, like the universe, are infinite.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.