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stars forming. But the impression I had was that the cluster occupied a vast, nearly empty cavity, the space between the stars glowing faintly in X-rays because of the high temperature, which now topped 10 million degrees in places. What gas clouds I saw were being flung about chaotically in all directions—not exactly the optimal conditions for organized gravitational contractions to create, or replenish, a cluster of nearly a million stars. Were conditions very different a million, 10 million years ago? Was the Galactic Center then full of dense, dusty clouds of gas, churning out all these stars in a giant burst of gravitational coagulation?
    I still do not know the answer to this question. The hypothesis offended my Copernican roots, because it would have meant that I was visiting the Galactic Center under special conditions, and it raised more questions than it answered. Why should I
have happened upon the Milky Way’s nucleus at just the “moment” (astronomically speaking) when rampant star formation had stopped but its shortest-lived products were still vital? Why was there no molecular gas in reserve anywhere near the present-day star cluster? I searched desperately for alternatives. Then, with little warning, one was thrust upon me: At least some of these young, massive stars must have formed from the collisions and mergers of smaller stars.
    Watching two stars collide and coalesce has to be one of the most spectacular sights in the Galaxy, but you have to be lucky to see it. Stellar collisions occur only once every few thousand years, and only in the centers of galaxies are the stars packed tightly enough for collisions to occur even this frequently. It is a safe bet that no stellar collision has ever occurred in the environs of the Sun.
    The whole concept of a stellar collision sounds violent, but what I witnessed was akin to a ballet. The dance begins tentatively, for only in rare cases do the stars hit head-on. Most often they barely brush one another and, if conditions are just right, glide into a delicate embrace. The collision, then, starts as a kind of pas de deux. The stars in question approached one another more slowly than I expected, at not more than a couple of hundred kilometers per second. I should not have been too surprised, because such speeds are typical of the stars located a few light-years from the Galaxy’s center of mass. But slowness was a crucial element in the encounter. If the mutual approach had been too fast, these stars would have sped past one another with little interaction, or (if aimed just so) they would have hit so hard that the outcome would have been ugly: bits of star splattered everywhere, but no long-term relationship.
    As the stars glided toward one another, their motions were gradually deflected from straight-line indifference to gently converging paths, and they sped up. I noticed the swellings that rose gradually on the sides of the stars facing one another, as well as on the opposite sides. Through these bulges, each star was responding to the other’s gravity, which is stronger on the near
side than at the star’s center, and stronger at the center than on the far side. (On Earth we get excited about the barely perceptible tides caused by the Sun and Moon, but they pale beside these distortions.) By now the partners were focused squarely on one another, stretched along their mutual axis. As they swung past each other, the bulges tried to follow, and for the most part they kept up. But stars do not like being distorted, and the deformation took its toll. The friction of each star’s continuous internal readjustment heated its interior, and the bulges began to lag behind the stellar motion. The bulges no longer lined up, and their gravitational attractions for one another stowed the stars and drew them closer together. I held my breath, because I knew that this was the crucial stage in the encounter. More often than not, capture would elude