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天文学家发现一颗系外行星，它的主恒星起源于银河系外，而且此恒星的金属含量明显少于模型预期中的带有行星的恒星。Christopher Intagliata报道
Astronomers have already discovered hundreds of exoplanets. But make way for the new kid. Which is orbiting a kind of star that models say it shouldn’t.
Researchers found the exoplanet while looking at the star HIP 13044—or Sergio, for Star of Extra-Galactic Origin. It’s in what once was a separate galaxy, which the Milky Way gobbled up billions of years ago.
The scientists saw Sergio wobbling due to the gravitational tug of a Jupiter-sized gas planet, which the scientists dubbed Sergio Junior [IAU name: HIP 13044 b]. They detail their find in the journal Science. [Johny Setiawan et al., "A Giant Planet Around a Metal-Poor Star of Extragalactic Origin"]
You don’t ordinarily find planets hanging around a star like Sergio. First, it's really old—past the Red Giant phase, when stars balloon in size and swallow up planets in close orbits. And planets tend to form around metal-rich stars, like our Sun. But Sergio has only one percent the metal content of our Sun. That doesn't jibe with one widely accepted model of planetary formation.
The Sergios may offer a glimpse of the future of our own planetary system—in about five billion years. We hope to be back then with an update.
—Christopher Intagliata
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