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SESK: Stuff Everyone Should Know · sesk.info/astro-microlensing-brightening

What happens when a foreground star microlenses a background star?

The background star is temporarily magnified.

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  1. Its light is magnified ✔
  2. It becomes physically larger
  3. Its spectrum loses all lines

Why: The foreground star's gravity curves light from the more distant star. Close alignment produces a temporary brightness increase, and a planet can add a smaller feature.

Huh, didn't know that: Microlensing can reveal planets far from their host stars.

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Microlensing makes a star brighter without giving it a bigger bulb.
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References

Answer: Its light is magnified. The foreground star's gravity curves light from the more distant star. Close alignment produces a temporary brightness increase, and a planet can add a smaller feature.

  1. Microlensing 101 science.nasa.gov/mission/roman-space-telescope/microlensing
    the nearer star acts like a natural cosmic lens, magnifying light from the background star
    Checked 2026-10-10.

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