Almost twice as ancient, star gives glimpse of sun's future
When the sun enters its twilight years, chances are it will look just like HIP 102152.
In terms of mass, temperature and chemical composition, the star HIP 102152 is the closest match to the sun ever found, astronomers announced August 28 at a press conference. But it’s also almost 4 billion years older, providing a tantalizing glimpse of what might happen to our 4.6-billion-year-old sun as it ages.
“Work with solar twins is helping us contextualize the sun as a star,” says Gustavo Porto de Mello, an astronomer at the Federal University of Rio de Janeiro who was not involved in the research. “This is another step toward finding stars that represent the sun at various stages of evolution.”
HIP 102152 has given the researchers insight on lithium, an element that exists in high amounts in some stars but is virtually absent in the sun. Some astronomers have wondered whether that makes the sun an outlier, Porto de Mello says. But the researchers found that HIP 102152 contains even less lithium than the sun, while a previously identified younger solar twin named 18 Scorpii has more. The findings suggest that the hot, churning interiors of sunlike stars gradually burn through lithium as the stars age. “This might be trying to tell us about the inner workings of the sun,” Porto de Mello says.
Like the sun, HIP 102152 has relatively low amounts of iron, magnesium and silicon, elements that tend to make up the bulk of the mass of rocky planets such as Earth. That could be a sign that the newly discovered star hosts planets, says study coauthor Iván Ramírez from the University of Texas at Austin. The researchers are using the La Silla 3.6-meter telescope in Chile to find out. So far they have ruled out the existence of Jupiter-mass planets, but small rocky ones are still possible.
Finding stars nearly identical to the sun is a difficult task because stars tend to have quirks and anomalies. Plus, it is time consuming and expensive to precisely measure a star’s properties.
An international team of astronomers has been hunting solar twins since 2006, when it began picking out promising candidates from a sky survey. One was HIP 102152, which is located about 250 light-years away in the constellation Capricornus.
Now the researchers have performed a detailed analysis with the European Southern Observatory’s Very Large Telescope in Chile, which will be published in Astrophysical Journal Letters. HIP 102152 is 97 percent as massive as the sun, 54 degrees Celsius cooler and has very similar abundances of more than 20 chemical elements. “It’s about as dead-on a twin as you could reasonably hope to find,” says David Soderblom, an astronomer at the Space Telescope Science Institute in Baltimore who was not on the research team.
At 8.2 billion years old, HIP 102152 is the oldest solar twin ever found. In less than 2 billion years, the star will run out of hydrogen in its core and start ballooning to hundreds of times its current size. When that happens to our star, the sun will fry Earth and probably engulf it.
Editor's Note: This story was updated on September 12, 2013, to correct the title of the journal in which the study was published.
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