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First of the Sun's long-lost siblings found; may host habitable worlds

This distant star in the constellation Hercules is a long-lost sibling to our Sun. (Credit: Ivan Ramirez/Tim Jones/McDonald Observatory)

This distant star in the constellation Hercules is a long-lost sibling to our Sun. (Credit: Ivan Ramirez/Tim Jones/McDonald Observatory)

By Scott Sutherland
Meteorologist/Science Writer
Monday, May 12, 2014, 12:29 PM

An international team of astronomers examining a star in the constellation Hercules have discovered that it is one of our Sun's long-lost 'siblings', and their findings may help us find more of our stellar family members that were scattered throughout the galaxy.

Nearly 4.6 billion years ago, a small part of an immense cloud of interstellar gas and dust collapsed in on itself, under the force of its own gravitational attraction, to form our Sun. Our Sun wasn't an 'only child' though. Astronomers believe that there were thousands to tens of thousands of other stars born from this same cloud, all part of a 'stellar family' to which our Sun belongs. The members of this family have since gone their own separate ways, scattering throughout the galaxy, but a recent survey of stars has located the very first of our Sun's 'solar siblings'.

Astronomers have found some stars our there that are nearly exactly like our Sun, in temperature, spectrum, chemical composition, etc., and these are typically called 'solar twins'. However, these aren't necessarily part of our Sun's family. In order to be counted as a sibling, a star needs to have the roughly same chemical composition, but also the motion of the star through the galaxy has to indicate that it was born in roughly the same area as our Sun.

The team identified over 30 nearby candidates to examine, but out of all those, only one made the cut: HD 162826, a star located around 110 light years away, in the 'arm' of the constellation Hercules

Compared to our own yellow G-type star, HD 162826 is a yellow/white F-type star, burning a little hotter and being roughly 15 per cent larger, so it's something of a 'big brother' to the Sun. However, despite these differences, the team of astronomers found that HD 162826 and our Sun have nearly the exact same elements inside it, and HD 162826's motion - its 'orbital dynamics' - through the galaxy match what they expected to see from a star that formed in the same area as our Sun.

"We want to know where we were born," study lead author Ivan Ramirez, an astronomer at the University of Texas at Austin, 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."

Relatives of our own?

Not only could this other star show us where we're from and help us to understand why we're here, but our own solar system and indeed our own existence may hint at the possibility of life-bearing planets orbiting HD 162826. Past surveys of the star haven't revealed any large planets orbiting close in - so called 'hot Jupiters' - but the possibility of smaller, Earth-sized planets hasn't been ruled out yet. If our own solar system's potential for life to form came from the combination of conditions in our parent cloud of gas and dust, or if only some of the stars in the 'family cluster' had the potential, but exchanged bits and pieces of planets and the like when they were much closer together, several of these solar siblings may host life-bearing worlds as well. According to Ramirez the chance is small, but he says "it could be argued that solar siblings are key candidates in the search for extraterrestrial life."

Along with this discovery, astronomers are excitedly waiting data from the European Space Agency's Gaia Space Observatory

"The number of stars that we can study will increase by a factor of 10,000," Ramirez said in the statement, which would allow his team and others to use the techniques they've developed to identify solar siblings halfway across the galaxy.

The research of Ramirez and his colleagues is set to be published in the June 1 edition of The Astrophysical Journal, and can be read online here.

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