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Video: The Planet That Wasn't

Credit: Jet Propulsion Laboratory/California Institute of Technology

The white orb in this video is more than meets the telescope lens. When astronomers saw red dwarf KOI-256 (large red object)—about 400 light-years away in the constellation Draco—dim every 28 hours or so, they first thought that a Jupiter-sized planet was passing in front. But upon looking closer at the Kepler space telescope data, they were surprised by how sharply the light dipped. Sensing something strange, the astronomers measured how much the red dwarf wobbled from the object's gravitational pull and found it wobbling 1000 times more intensely than it should. It turned out that the "planet" was actually a collapsed star, the researchers report in an upcoming issue of The Astrophysical Journal, and the dimness was caused when the smaller star passed behind KOI-256, blocking its light. When the astronomers returned to the Kepler data to look for the collapsed star passing in front, they found a surprisingly mild dip in brightness. That's because, although the tiny star is Earth-sized, it's as massive as our sun and about 75,000 times as dense as KOI-256. So its intense gravity acts as a lens, magnifying KOI-256's light in Earth's direction.

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