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article imageAstronomy: Sun's ‘long-lost brother' found, more siblings sought

By Robert Myles     May 11, 2014 in Science
Austin - Researchers have identified what they say is a close relative of our Sun — the first “sibling” of our own star — born out of the same cloud of gas and dust.
The research team’s methods may aid the search for other brother-and-sister stars of our Sun, leading to a better understanding, not just of how and where the Sun formed, but also how our solar system and Earth in particular, came to be hospitable for life.
Ivan Ramirez, an astronomer at University of Texas at Austin led the research team and their findings will be published in the June 1 issue of The Astrophysical Journal.
Commenting, Ramirez said, “We want to know where we were born — if we can figure out in what part of the galaxy the Sun formed, we can constrain conditions on the early solar system. That could help us understand why we are here.”
The UTexas researchers identified a star, 15 percent as big again as our Sun, called HD 162826.
HD 162826 lies about 110 light-years distant. Although it can’t be seen with the naked eye, it can be spotted, using binoculars, in the constellation Hercules, not far in the sky from Vega, one of the brightest stars in the sky. The accompanying star-chart from the McDonald Observatory clearly shows the location of HD 162826 in relation to Vega.
Researchers homed in on HD 162826 as the Sun’s sibling out 30 possible candidates advanced by several groups around the world engaged in the search for close relatives of the Sun. Ramirez’ team studied 23 of these stars in detail using high-resolution spectroscopy to gain a fuller understanding of each star’s chemical make-up.
But the team didn’t just use spectroscopic fingerprints as part of their detective work; they also drew on information concerning likely suspects’ movements. In so doing, HD 162826 emerged as having the same family lineage as the Sun.
To pinpoint the Sun’s sibling, the team used information about stars’ orbits — both historical and projected — around the center of our Milky Way galaxy. This specialism of astral dynamics crossed the political divide and the Texas team were assisted by two experts in this field, A. T. Bajkova of the Pulkovo Astronomical Observatory and V. V. Bobylev of the State University, both in St. Petersburg, Russia.
The tantalizing prospect, highlighted by Ramirez is that there’s a smidgen of a chance, “small, but not zero,” that solar sibling stars like HD 162826 could host planets where life exists. When such sibling stars formed in their birth cluster, an estimated 4.5 billion years ago, collisions might have knocked lumps off planets. These planetary fragments could have wandered off in space before encountering other solar systems, conceivably seeding primitive life on Earth.
That process might also have worked in reverse. Earth is known to have been hit by large objects in the past. If, at the time of such world-shaking collisions, life had already taken hold on Earth, then perhaps shards of our Earth could have given a piggyback to primitive life-forms that ultimately found a home on planets orbiting solar siblings.
Following that reasoning, said Ramirez, “Solar siblings are key candidates in the search for extraterrestrial life.”
But Ramirez stresses the discovery of one solar sibling should be seen in the wider context of gaining an understanding of where the Sun, our solar system and Earth itself all started off. In that quest, scientists anticipate a flood of data once space-based telescope’s like the European Space Agency Gaia ‘billion-star surveyor’ start returning data.
In the 4.5 billion years or so since the Sun started its life as part of a cluster of maybe 1,000, possibly 100,000 stars, such is the scale of what is presently unknown, as Ramirez says, “A lot of things can happen in that amount of time.”
Stars that were part of the original cluster will have gone their separate ways, now tracing their own orbits around the Milky Way’s galactic center. Some, like HD 162826 may be relatively close but others will lie at much greater distances.
That’s where Gaia comes in because its star survey won’t just be limited to close neighbors of the Sun. Gaia will provide accurate distances and proper motions for a billion stars. That will allow astronomers to search for solar siblings all the way to the center of the Milky Way. Ramirez estimates that Gaia will increase 10,000-fold the number of stars astronomers can study.
Gathering data is the easy part, however. Each star will still require careful individual study to pick out the ones that are truly of the same blood-line as our Sun. As Ramirez put it, it isn’t a case of “we’re going to throw this data into a machine and it’s going to spit out the answer — it’s not that simple. You have to be careful, do things the old way: star-by-star analysis.”
But once many more solar siblings have been identified, there’s the prospect of us learning where we came from, at least in the astronomical sense. Astro-dynamics specialists will be able to construct models that run the orbits of all known solar siblings backwards in time.
At the point where they intersect, that’ll be where our Sun originated.
It won’t tell us the answer to life, the Universe and everything, but it might just give us a starting point.
More about solar siblings, origin of solar system, Sun's longlost brother, Astronomy, HD 162826
 
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