60-Second Space

Oddball Eclipse Makes Star Brighter

When a white dwarf passes in front of its binary star system companion every 88 days, it acts like a lens to make the larger star appear brighter to us.


Eclipses are supposed to make things go dark: the moon blocks the sun, and day turns to night. Now astronomers have accidentally discovered the opposite: an eclipse that makes a star brighter.
Thank Einstein. And Kepler—the space telescope, not Johannes. Launched in 2009, Kepler watched more than 100,000 stars, looking for tiny dips in a star’s brightness caused by orbiting planets when they pass in front of their sun.

But one star didn't get the memo. Every 88 days, it brightens slightly.

Researchers realized that they were actually seeing a binary star system. One of the pair is big and bright like our sun. The other is a white dwarf—a small, dim star a little larger than Earth, but so dense that a spoonful weighs tons.

Because of its high mass, when the white dwarf passes in front of its mate its gravity bends and amplifies the larger star's light, just as Einstein said. In other words, the white dwarf acts like a lens that makes the bigger star appear brighter during the eclipse. The report is in the journal Science. [Ethan Kruse and Eric Agol, A Self-Lensing Binary Star System]

Black holes that orbit stars should do the same thing. So someday someone might find a black hole by looking for the light.

—written by Ken Croswell, voiced by Steve Mirsky

[The above text is a transcript of this podcast.]

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