Distant, Big Galaxies Caught Cannibalizing Smaller Ones
Stellar streams around the spiral galaxy M 63 show remnants of a satellite galaxy that M 63 has swallowed. The central part is an ordinary positive image; in the outer regions, the negative of the image is shown (darker areas show brighter light). In this way, the faint structures that are the target of this survey are more readily discerned.
Credit: D. Martínez-Delgado (MPIA)

Massive, distant galaxies have been spotted gorging on smaller ones to build up their bulk in a far-flung cannibal feast, scientists report.

Galactic cannibalism has been seen before ? even the Milky Way is guilty ? but now scientists have observed the cosmic behavior in distant galaxies beyond our cosmic neighborhood. [Photo of cannibal galaxy at work.]

As they are digested, smaller dwarf galaxies are severely distorted, forming structures such as spindly tendrils and stellar streams that surround their captors.

These star streams, called tidal tails, form because of the stronger gravitational pull on the near side of the small galaxy compared to the far side. Stars closer to the parent galaxy are pulled in more quickly, while stars farther away lag behind.

In the new study, the tidal tails were discovered around spiral galaxies at distances of up to 50 million light-years from Earth.

The observations were collected by an international group of researchers ? led by David Mart?nez-Delgado of the Max Planck Institute for Astronomy and Instituto de Astrof?sica de Canarias in the Spanish Canary Islands ? working with amateur astronomers using amateur telescopes and commercially available CCD cameras.

The study found that major tidal streams with masses between 1 and 5 percent of the galaxy's total mass are quite common in spiral galaxies. The discovery will be detailed in the October issue of the Astronomical Journal.