Or, perhaps a modest black hole once roamed the universe alone, eventually attracting the gas that later formed our galaxy and stars.

It does seem probable that the Milky Way's black hole went through a growth phase. It may have acquired more black holes, neutron stars and other "dark matter" during additional galactic smash-ups. Or, it may have slowly attracted the stellar black holes manufactured right in its own galaxy. Even in this day and age, Ghez says she expects to find small black holes headed like invisible rocks toward the supermassive black hole.

After a growth spurt, perhaps middle age sets in. Although our black hole is huge, it is categorized as "quiescent." Unlike an "active galactic nucleus," which blazes with radiation as it pulls in a thick disk of gas and shredded stars, our black hole sits in a wispy disk of fuel, and emits only weak radiation. In astronomical terms, it is not sucking loudly like a flushing toilet. It doesn't stand a chance of swallowing the Earth, Ghez says. It probably will never snare even her close-orbiting stars, although one has mysteriously disappeared. "This black hole is supermassive," she says, "But it's still only a small fraction of the mass of the galaxy."

Theoretically, our black hole, and all others, will eventually fade and die, although Ghez confesses no clue as to how such an event would unfold.

Quiescent though it is, you would not want to go skating around the black hole. That is strictly for professionals.

"When you get very close to a black hole, the pull of gravity on your feet is much stronger than on your head," Ghez warns. "Your experience would be that you'd get torn to shreds — well, we call it 'tidally disrupted.'"

Feet first, you'd be yanked over the "event horizon," the boundary around the black hole. Your loved ones, Ghez says, would never see you disappear. They'd just note that you were moving slower and slower.

"One of the oddities of relativity," she says. Your tidally disrupted matter, however, would whirl toward the center, approaching the speed of light, light whirling in with you.

Your destination would be the "singularity" at the center of this mind-boggling density. For the sake of comparison, consider a neutron star, that compressed-iron core left behind after a massive star explodes most of its gas into space. The density of a neutron star is, according to the cocktail-napkin calculations of supernova scholar Stanford Woosley, similar to 800 million elephants jammed into a cubic inch. The density of the singularity at the center of our black hole is greater than that, to a degree that is even more unfathomable.

Ghez remains unfazed, however. With her new-and-improved way to drive stakes into the galactic ground, she continues in pursuit of our black hole.