A nice little piece demonstrating how scientists ideas can change.

A mysterious cosmic signal radiating from the center of our Milky Way galaxy is actually triggered by ancient stars, rather than dark matter, according to a new study.
There is a mysterious abundance of high-energy gamma-rays at the Milky Way's core, also known as the galactic bulge. Previous studies suggested that this abundance originated from dark matter the mysteriously invisible substance that does not emit light or energy, yet is thought to make up most of the matter in the universe.
Instead, new research shows that the gamma-rays emanate from thousands of rapidly spinning neutron stars known as millisecond pulsars, which are believed to be some 10 billion years old.
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