WHEN two dwarf galaxies meet, the larger one will steal almost all of the smaller galaxy鈥檚 stars.
It had been a mystery how some dwarf galaxies can be so devoid of stars, while remaining full of dark matter. Now computer simulations by Elena D鈥橭nghia of Harvard University and colleagues have shown show that it can happen when a smaller galaxy starts orbiting a larger one.
The orbital period sometimes ends up matching the time it takes the smaller galaxy to complete one spin on its axis. This 鈥渞esonance鈥� means that the small galaxy feels a constant tug which strips out its stars.
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The dark matter around the smaller galaxy is not rotating, however, so after a few billion years, it is virtually all that is left of the small galaxy. 鈥淚t is only a few per cent that is normal matter,鈥� says D鈥橭nghia (Nature, ).
