Studying galaxies and clusters in many wavelengths of light tells astronomers more than a single image ever could. Imaged with the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, NGC 4666 lies some 80 million light years from Earth in the constellation Virgo. All looks calm and peaceful, however the bright centre of this galaxy is actually the site of clashing, titanic forces where new stars are blazing into existence. Very active star-forming galaxies like this are known as starburst galaxies. But why do some galaxies form stars much more rapidly (and apparently more efficiently) than others? What makes a galaxy a starburst galaxy?
Making stars is easy: you just need to arrange for huge quantities of hydrogen to be squeezed together. This is just what we see here. Stirred by the gravitational pull of other nearby galaxies such as NGC 4668 (lower left of image), clouds of cold interstellar gas in NGC 4666 are colliding. As a result NGC4666 is pumping out new generations of stars. Starbursts are short-lived events, stars are forming so quickly that the reservoirs of interstellar gas from which stars are coalescing would be used up on a timescale much shorter than the age of the galaxy
Starburst galaxies are exciting, turbulent places. Strong stellar winds from giant new stars in the starburst region combine with the blasts of supernovae to push a mighty flood of extremely hot gas, a “superwind” from the galaxy thousands of light years into intergalactic space. Alas the superwind is too tenuous to see in visible light, but has been observed in X-rays by the European Space Agency’s XMM-Newton space telescope.
There is much, much more to the Universe than meets the eye.