HD 162826 and the Sun go way back.
A nebular nursery. Image via ESO/S. Guisard.
When siblings are parted at birth, it can take a lot of detective work and creative thinking to track them down in later life. As it turns out, the same is true for the Sun's crib mates. It has been 4.5 billion years since our star was born alongside its many thousands of siblings, and since then, they have been flung across the galaxy to very different fates. Searching for them is like rooting out a needle in a galactic haystack.
Now, for the first time ever, scientists, based out of the University of Texas at Austin, have managed to find one such needle. HD 162826 is 15 percent more massive than our Sun, and is about 110 light years away in the constellation Hercules. It's not visible to the naked eye, but it is bright enough to be seen through binoculars.
Astronomers had been observing the star for almost two decades without realizing it's the long-lost sister of the Sun. No doubt we have catalogued other solar siblings whose common heritage has yet to be discovered. Indeed, the UT team, lead by astronomer Ivan Ramirez, is confident that the identification of HD 162826 is just the beginning.
“We want to know where we were born,” Ramirez said in a statement. “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 basic idea is to press rewind on the orbit of a candidate star, to see if its path had ever dovetailed with the Sun's trajectory. That's definitely easier said than done, so two leading experts in dynamics—the study of stellar movement through the galaxy—were invited to crunch the numbers. A. T. Bajkova of the Pulkovo Astronomical Observatory and V. Bobylev of St. Petersburg State University narrowed down the field of candidate stars to 30.
Ramirez's team studied the candidate stars at the McDonald Observatory. Image via Zereshk.
That's when the other qualification for stellar sisterhood entered the equation. Just as biological siblings share much of the same DNA, solar siblings share key chemical elements. In the case of our Sun, the smoking guns are barium and yttrium. When Ramirez's team examined both the chemical signatures of the stars and their dynamic pasts, HD 162826 was the only one to fit the profile. The team's methods will be published in the June 1 issue of The Astrophysical Journal.
One of the most exciting consequences for seeking out more solar siblings is the likelihood that these stars support planets, and possibly even life. Back when the Sun's siblings were all hanging out in their nursery together, there would have been a robust, inter-system exchange of planetary material and chemical runoff. Enriched chunks of early Earth could have been launched into other fledgling solar systems, seeding the potential for life on other planets.
Or, perhaps the opposite is true, and the ingredients for life were sprinkled on Earth from worlds that are now thriving hundreds of light years away. Either way, according to Ramirez, “it could be argued that solar siblings are key candidates in the search for extraterrestrial life.” The idea that we might have genuine biological relatives on planets orbiting distant solar siblings is certainly tantalizing.
The UT team's search is far from over, and they are already collecting data on stars from every corner of the Milky Way. “The number of stars that we can study will increase by a factor of 10,000,” Ramirez said, referring to the new data being collected by the ESA's Gaia space observatory.
It looks like the Sun's family is about to get a lot bigger.