March 14, 2012 | 5
We all come from somewhere. If you wind the clock back far enough, we all come from the same place. Sometime about 4.5 billion years ago, the sun was born, and a disk of debris swirling around it soon coalesced into Earth and the rest of the planets. But where did that happen? Where was the sun born?
Most stars seem to have been born in clusters or groups. Assuming the sun did the same before venturing out on its own, some remnant of the sun’s native cluster might still exist within the galaxy. And inside that cluster would reside stars born in the same chemical environment, at around the same time, as the sun. Those stars, in short, would be the long-lost siblings of the only star in the universe that we know to support life.
Bárbara Pichardo of the National Autonomous University of Mexico and her colleagues in Mexico, the U.S., Italy and Germany looked into a possible solar origin within M67, a cluster of stars about 3,000 light-years away. M67 qualifies as relatively nearby within the Milky Way Galaxy, which is about 100,000 light-years across. In addition to its proximity, the cluster has a number of attributes that make it an attractive candidate for the sun’s birthplace. Its stars are about the same age as the sun, and their chemical makeup is strikingly sunlike as well. Astronomers have already found a number of stars within M67 that look to be dead ringers for the sun.
But that may just be coincidence. Pichardo and her colleagues ran computer simulations to wind the galactic clock back billions of years, looking for a time when the sun and M67 were close together. If the sun was somehow ejected from a cluster, after all, its orbit and the orbit of the cluster must have intersected at some point in the past.
After simulating 350,000 possible paths that the sun and M67 may have taken through the galaxy to reach their present locations, the researchers concluded that the sun could not have emerged from M67. The only way that the sun could have sprung from that cluster, they found, was if it had been ejected at a velocity great enough to disperse a nascent solar system or the makings thereof. In other words, our existence, and the existence of our host planet, is evidence that the sun never underwent such a violent ejection.
One important caveat, though: the computer simulations assume that the familiar spiral arms of the Milky Way are stable, unchanging structures. But some studies have indicated that the arms of spiral galaxies may in fact be transient. If that were the case, the researchers note, the hypothesis of M67 as the sun’s birthplace might itself be reborn.
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