Okay, hold the presses right there. Zwart is arguing that the sun and a cluster of similar-composition, same-age clonelike stars were created in a small cluster and over time drifted away from each other. However, early on (age 1.8 M years) a fellow similar star in the cluster decided it was time to blow up! That is a much more plausible explanation for the isotopic content of some "pristine" meteorites left over from our solar system formation. Moving right along:"...many astronomers now think [the Sun] was one of 1000 or so siblings all born at nearly the same time... The cluster into which the Sun was probably born is now long gone. ...I have pieced together available data and made an educated guess as to what [this cluster] might have looked like. From these inferred properties, I have calculated the possible trajectories of former cluster members through the galaxy to figure out where they might have ended up.
Based on [various] isotopic measurements, Leslie Looney of the University of Illinois... argued in 2006 that a supernova went off within a distance of 5 light years when the sun was scarcely 1.8 million years old. ...The supernova might have been as close as 0.7 light year. ...Was a massive star simply passing by when it decided to blow up? ..A much more plausible explanation is that the newborn sun and the exploding star were fellow members of a cluster. With stars packed so tightly together, a close supernova would not have been so improbable."
Orbital mechanics is Dr. Portegies Zwart's specialty. His simulation places the birthplace of the sun 33,000 LY from the center of the galaxy and 200 LY above the galactic plane, puzzling, he says, because the outer reaches of the galaxy are poorer in heavy elements than the inner parts. The sun, based on its higher proportion of heavy elements, should have been born some 9000 LY closer to the center of the galaxy. "Maybe the supernova (now a given) that seeded meteorites with iron 60 also enriched the sun with heavy elements. Or maybe my orbital calculations went astray because the gravitational field of the galaxy has changed or because the sun's orbital path was diverted slightly by the gravity of nearby stars or gas clouds."What is puzzling is that the sun's orbit, traced back in time, suggests our solar system was born farther out in the galaxy than it is now
Many things can go wrong when you are making so much up based on a shortage of evidence. The good doctor wavers between the conditional voice ("perhaps"... "maybe"... "should be orbiting... etc.) and the positive, "this is the way it was" tone, implying confidence in the conclusions despite the stacking of inferences upon maybes and pulling a supernova out of the vacuum to go off a carefully estimated (well, within two orders of magnitude: either 5 LY or 0.07 LY) distance from baby Sun. That's a handy supposition.
The answer to the nagging question, "Does Dr. Potegies Zwart actually report finding one or more of these putative siblings of the sun from that hypothesized early cluster of 1000 sibling stars?" Well, not to put too fine a point on it, no. The sibs should be orbiting about the galaxy at 200 km/s, but their relative motion to that of the Sun is only "a few" km/s. Using this precise figure of separation, Dr. P-Z states that after 27 orbits around the galaxy, the brother stars should be spread out along an arc halfway around the galaxy. That seems to make finding the long-lost sibs pretty hard, but some (50) of the brothers and sisters (both genders, apparently: scatalogical Fun With Stars!) should [there's that word again] be within 300 LY of our current location. One of his students is now looking for them in the Hipparcos catalog, in the galactic plane of our sun, ahead of and behind us along our orbital track.
Unfortunately, Hipparcos was "probably [there's another disclaimer] not precise enough to make a positive identification." For such precision [and to keep grad students employed in the onerous tasks of trying to identify brother and sister suns],
There's a call for an annuity if I ever saw one. "Theorists will be able [with all these data] to compute the birthplace of the sun with greater certainty and determine, for example, whether the gravitational field of the galaxy has changed substantially or not."For that, we will need the GAIA spacecraft. It has a pair of telescopes that will measure the full three-dimensional position and velocity of some one billion stars over five years, creating an essentially complete census of stars within several thousand light years of the sun. ...In the data, we can look for stars that lie nearly along the sun's papst and future orbital path. Their composition should look like the sun's, because the same supernova that polluted the early solar system will have done the same to other stars in the cluster.
It's all about gravity, in the end. In 1996, Begelman and Rees wrote, in their Scientific American Library book, Gravity's Fatal Attraction, "Gravity is the one truly universal force. ...Every significant level of structure in the Universe - stars, clusters of stars, galaxies, and clusters of galaxies -- is maintained by the force of gravity."
This is the orthodoxy of today, as well. Nothing has changed, except for more and better data, which can be parsed to find bits that support this viewpoint. This is why, after reading Dr. Portegies Zwartz's story, I wrote Ms. Mariette DiChristina, SA's acting editor in chief, to advise her why I am not going to be renewing my years'-long subscription to their blindered rag. I suggested politely that science is about ideas after all and that they might do their readers a service by airing out other ideas of how things work, too, that are ignored or dismissed or trivialized by their contributing cadre of scientists and PR folks from federal agencies in the face of increasing evidence to the contrary. Exposing other ideas does not make them right, or wrong - it simply exposes them to scrutiny and consideration, one hopes in the spirit of scientific even-handedness. I also expressed my dim view of the chances of that ever happening.
As H.L. Mencken so wryly and aptly put it, last century:
Jim"For every problem there is a solution that is neat, plausible, and wrong."