Something is killing-off galaxies by preventing the birth of stars—and astronomers now think they know why.

While studying 51 galaxies in a “galaxy-cluster” called the Virgo Cluster an international team of scientists have found that molecular gas—the fuel for new stars—is being “swept away by a huge cosmic broom.”

Exactly what is preventing nearby galaxies from birthing new stars has been a long-standing mystery in astrophysics. The new paper, now available online, blames the extreme environment of the Virgo Cluster. It’s been accepted by the journal Astrophysical Journal Supplement Series.