Andromeda galaxy eats its neighbors

Astronomers have so far drawn the fullest picture of galaxy evolution

PAndAS map of the neighborhood of the Andromeda galaxy (top right) including the triangle nebula (bottom left). The colors stand for different star densities: red color indicates that there are many stars in the respective region; From red to yellow, green, light and dark blue, the number of existing stars decreases. In the (red) centers of highest density, images of the Andromeda galaxy and the triangle nebula are inserted, showing these galaxies as they appear on telescopic images. The distribution of the stars shows complex structures: star streams, arcs and some dwarf galaxies. A number of these structures have been rediscovered within the framework of the research described here, and none of the structures has so far been depicted as detailed as here. The dotted circles have diameters of about 900, 000 and about 300, 000 light years, and mark the target areas of the survey. On the top left, the full moon slice is drawn to scale for size comparison. © A. McConnachie / NRC; Triangulum disk courtesy of TA Rector and M. Hanna
Read out

New observations on astronomers in Nature report the most complete and detailed picture of processes in galaxy evolution so far. They show the remnants of smaller galaxies that have been "eaten" by the Andromeda galaxy.

In traditional models, the key element in the evolution of galaxies - accumulations of billions of stars held together by gravity - is cannibalism: more massive galaxies are created by the fusion of smaller galaxies, and they continue to grow by becoming more galaxies incorporate.

Only in the last five years have astronomers in our home galaxy, the Milky Way, and in some of the more remote galaxies been able to detect evidence of such acts of galactic cannibalism: stellar streams - very long accumulations of thousands of stars orbiting around the galaxies as in formation flight, Compared to the many stars in the disk of our Milky Way galaxy, these stellar streams are very weak and therefore difficult to detect.

A stroboscopic projection of results of a detailed numerical simulation of a possible orbit of the triangle nebula around Andromeda. Andromeda is the circular disk to the right of the center of the picture. The shape of the triangle nebula, which is shown here in different phases of its orbit, changes under the gravitational influence of the larger galaxy. The simulation suggests that Andromeda will eventually incorporate the triangular nebula. John Dubinski

Andromeda galaxy screened

Now, new results of the international project PAndAS - "Pan-Andromeda Archaeological Survey" - paint the most complete and detailed picture of such stellar currents in the vicinity of a galaxy. PAndAS performs an extensive survey of the Andromeda Galaxy (M 31) and its surroundings. At a distance of 2.5 million light-years, it is the closest other spiral galaxy to our home galaxy. Its central region can be seen in the sky with the naked eye as a diffuse stain.

Nicolas Martin from the Max Planck Institute for Astronomy, who was involved in the data analysis, explains the results: "Astronomers have already found traces of such stellar currents. But only now has it been possible to create such a detailed map of a star-flow area. The pictures show six different currents. Two of them are new discoveries. None of the currents had previously been measured as accurately as in the PAndAS study. The new data is the starting point for attempts to understand the evolution of the Andromeda galaxy over the last billion years. display

The Andromeda Galaxy, taken with the Schmidt Telescope of the Calar Alto Observatory. Kurt Birkle / MPI for Astronomy

Star streams as remnants of dwarf galaxies

In the words of Martin: "The stellar streams are the remnants of dwarf galaxies that have taken on andromeda galaxy. So we caught a galactic cannibal in the act. The stars will dissipate over the next billion years. Then nothing will indicate that these stars were once part of another galaxy

The story of the Triangle Nebula, a smaller companion galaxy by Andromeda, must also be rewritten in the light of the new findings. Martin again: "Until now, the triangular mist was just a companion to Andromeda. Now we have convincing evidence that the two galaxies were involved in a collision a few billion years ago. "This is shown by a newly discovered" star tail "of the triangle nebula, which, in this encounter, by the action of gravity Andromeda galaxy may have arisen.

(Max Planck Institute for Astronomy, 04.09.2009 - DLO)