Where are the sun's siblings?
Most stars form in groups inside of gas clouds. But scientists aren't sure where the sister stars of the sun went. A new survey of the chemical makeup of 350,000 Milky Way stars could soon shed light on the mystery.
Scientists are looking for stars that match the chemical composition of the sun, which would confirm that they formed in the same gas cloud roughly 4.5 billion years ago. While seeking the sun's long-lost siblings, astronomers will also learn more about how the Milky Way formed.
"This survey allows us to trace the ancestry of stars, showing astronomers how the universe went from having only hydrogen and helium — just after the Big Bang — to being filled with all the elements we have here on Earth that are necessary for life," Martin Asplund of Australia National University said in a statement.
The survey, called GALactic Archaeology with HERMES, or GALAH, gathers information from HERMES, which uses a technique called spectroscopy to look at the abundance of elements in a star. HERMES is housed on the 3.9-meter Anglo-Australian Telescope at ANU's Siding Spring Observatory.
"The formation and evolution of galaxies is one of the great outstanding problems of modern astrophysics,” states the GALAH website. “The goal of galactic archaeology is to reconstruct the lost stellar substructures of the early Milky Way, thereby obtaining a detailed physical picture of its formation and evolution.”
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The universe was formed in an explosive event called the Big Bang about 13.7 billion years ago. About five minutes after the event, the universe was made up of 75 percent hydrogen and 25 percent helium. But as stars formed and began burning up those gases, they created more complex elements such as carbon, neon, oxygen, silicon, and iron.
As the stars ran out of elements to burn, they either exploded or shed their outer layers, depending on how massive they were. Either way, they dispersed elements throughout the cosmos.
"The next generation of stars forms out of this enriched material and, upon its death, releases the complex elements it produced,” the GALAH website explains. “Over time, the chemistry of the universe gets increasingly complex and varied thanks to this cycle of stellar recycling.”
GALAH isn't the only star survey underway. The European Space Agency's Gaia spacecraft aims to map more than one billion stars in the Milky Way. The next major data release will take place on April 23.
"Gaia is compiling the largest astrometric catalogue ever created, enabling investigations into the Milky Way's origin and evolution," the European Space Agency stated. "And there is more: The satellite has also been measuring stellar brightnesses and colors and has been taking spectra of the brightest stars in its survey."
The two surveys complement one another. While Gaia will focus more on mapping positions, motion, and distances, GALAH will examine temperatures and metallicity — the proportion of elements that are not hydrogen or helium — for all stars, not just for the brightest ones, as Gaia does. The combined surveys will help determine the timeline of galaxy development.
Research papers based on GALAH data can be found on the mission's website.