Galactic prang fingered in star formation mystery

Gas + shock waves = shiny things

By Lucy Sherriff, 30th March 2005

Astronomers now have direct evidence that stars form when galaxies collide. Data from the ISO, the European Space Agency's (ESA) infrared observatory, has shown that the shock wave caused by the collision of two galaxies has excited the gas from which new stars form. The discovery could shed light on how the first ever stars formed.

Excited gas in the overlapping parts of the two galaxies known as Antennae

It has been known for a while that shock waves from supernovae excite clouds of gas, which causes the cloud to collapse and eventually to form a new star. Hydrogen molecules radiate at a particular frequency when they are excited by this process, and it is this signature that scientists have spotted in the colliding galaxies known collectively as Antennae. The region where they overlap is very rich in excited molecular hydrogen.

The two galaxies are located 60m light-years away in the constellation 'Corvus'. They are at a very early stage (relatively speaking) in their encounter. Although the excitation of the gas has been detected, there are relatively few supernovae in the region which means that winds from these massive explosions cannot be responsible for getting the hydrogen all worked up: it has to be a result of the collision.

The researchers now believe that shock waves from collisions of early clouds of gas could have triggered the formation of the very first stars.

The researchers from the AIRUB Institute in Bochu and the Max-Planck-Institut für Astronomie in Heidelberg estimate that new stars will be born over the next million years or so, causing the galaxies to become twice as bright in the infrared.

The results will be published in full in Astronomy & Astrophysics, this spring.®