ASTRONOMERS FIND THE FIRST SIBLING OF THE SUN

A team of researchers has identified for the first time a star directly related to the Sun, one almost certainly born from the same cloud of gas and dust.

The find, led by astronomer Ivan Ramirez of The University of Texas, will help astronomers look for other solar siblings. It could lead to an understanding of how and where our Sun formed, and how our Solar System became hospitable for life.

“We want to know where we were born,” Ramirez said. “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.”

Additionally, there is a chance, “small, but not zero,” Ramirez said, that these solar siblings could host planets that harbour life.

In their earliest days within their birth cluster, he explains, collisions could have knocked chunks off of planets, and these fragments could have traveled between solar systems, and perhaps even may have been responsible for bringing primitive life to Earth.

“So it could be argued that solar siblings are key candidates in the search for extraterrestrial life,” Ramirez said.

The solar sibling his team identified is called HD 162826, a star 15 per cent more massive than the Sun, located 110 light-years away in the constellation Hercules. The star is not visible to the unaided eye but can be seen easily with low-power binoculars, not far from the bright star Vega.

HD 162826

The star is not visible to the unaided eye but easily can be seen with low-power binoculars, not far from the bright star Vega. Image credit: Ivan Ramirez/Tim Jones/McDonald Observatory

Following up on 30 possible candidates found by several groups around the world looking for stars in the Sun’s family, Ramirez’s team studied 23 of these stars in depth with the Harlan J. Smith Telescope at McDonald Observatory.

The remaining stars (visible only from the southern hemisphere) were studied with the Clay Magellan Telescope at Las Campanas Observatory in Chile. They used high-resolution spectroscopy to get a deep understanding of the stars’ chemical make-up.

In addition to chemical analysis, his team also included information about the stars’ orbits around the centre of the Milky Way galaxy. Considering both chemistry and orbits narrowed the field of candidates down to one: HD 162826.

By “lucky coincidence,” Ramirez said, the McDonald Observatory Planet Search team has been observing HD 162826 for more than 15 years. Studies by The University of Texas’ Michael Endl and William Cochran, together with calculations by Rob Wittenmyer of the University of New South Wales, indicate that it’s unlikely that any gas giant planet like Jupiter orbits the star. The studies do not rule out the presence of smaller terrestrial planets.

The project’s larger purpose is to create a road map for how to identify solar siblings, in preparation for the flood of data expected soon from surveys such as Gaia, the European Space Agency mission to create the largest and most precise 3-D map of the Milky Way. Gaia will provide accurate distances and proper motions for a billion stars.

Ramirez’s team has identified the elements barium and yttrium as particularly useful. They vary greatly among stars, which otherwise have very similar chemical compositions, largely dependent on where in the galaxy the star formed. Ramirez says his team’s road map will speed up the process of narrowing down the field of potential solar siblings.

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