Merger Of 2 Spiral Galaxies Leads To Unusual Cosmic Spindle Formation

Galaxies come in many shapes and sizes, and according to our current understanding, the large umbrella groups of elliptical and spiral galaxies make up the bulk of the galaxies in the known universe. And if we leave aside the so-called irregular galaxies, there are the lenticular galaxies, among which are the very unusual but not-so-rare spindle galaxies.

Only a dozen of these spindle-shaped curiosities had been observed till recently, but eight more have now been added to the list, and researchers have also suggested a mechanism that could be responsible for the creation of these cigar-shaped galaxies.

Properly called prolate rotators, these galaxies are likened to spindles not just for their shape but also for the fact that they spin along their lengths. A systematic study of data from the Calar Alto Legacy Integral Field Area (CALIFA) Survey — 600 galaxies were mapped with imagine spectroscopy at the Calar Alto Observatory in Spain — showed researchers eight new spindle galaxies, taking their total known count to 20.

Led by Athanasia Tsatsi of the Max Planck Institute for Astronomy (MPIA), Germany, the researchers also published a paper last Thursday in which they proposed an explanation for the existence of these spindle galaxies. They form when two large spiral galaxies collide at right angles to each other, and then merge. One of the spiral galaxies, under the influence of the other’s gravity, develops an elongated structure (technically called a “bar,” which is very common among spiral galaxies) and stars from the other spiral galaxy end up orbiting this long structure, leading to the final cigar-like shape.

While this mechanism explains the shape and observed spin of spindle galaxies, it also predicts some other properties that will require further observations to confirm or negate, the researchers said in a statement Thursday on the MPIA website. These additional observations could be made using “instruments like MUSE, the Multi Unit Spectral Explorer at ESO's Very Large Telescope, an 8-meter-telescope at Paranal Observatory in Chile,” they added.

Spindle galaxies aren’t always lenticular, though; they can also be elliptical. Merger of galaxies is also one of the theories for the formation of lenticular galaxies.

The study was titled “CALIFA reveals prolate rotation in massive early-type galaxies: A polar galaxy merger origin?” It appeared online Oct. 12 in the journal Astronomy & Astrophysics and its authors included researchers from Europe and Asia.