The rate of star formation might play a bigger role in affecting a galaxy's shape than previously thought, according to a recent study.
Galaxies, a smattering of dust, gas and stars glued together by gravitational attraction, come in all sorts of shapes and sizes. Edwin Hubble's classic "tuning fork" diagram describes four different types: ellipticals, disk-like lenticulars, spirals and irregular galaxies.
The lack of a defined structure and a large bulge where old stars and gas are concentrated have led scientists to believe that ellipticals are formed when two smaller galaxies merge together.
But a paper published in The Astrophysical Journal shows that a burst of star formation will cause a galaxy's center to puff up in size. The concentrated material dominates the galaxy's evolution, and over time it mellows out to become an elliptical or lenticular galaxy.
Ken-ichi Tadaki, lead author of the paper and a postdoctoral researcher at the National Astronomical Observatory of Japan, said: "Massive elliptical galaxies are believed to be formed from collisions of disk galaxies. But it is uncertain whether all the elliptical galaxies have experienced galaxy collision. There may be an alternative path."
By inspecting the light from different galaxies from 11 billion years ago, the researchers can see what the galaxies looked like in the past, three billion years after the Big Bang. It's a time when star formation was most active.
The Hubble Space Telescope captures the ancient light, allowing scientists to see the shape of the galaxies. The Atacama Large Millimeter/submillimeter Array, a series of radio telescopes in Chile, examines the amount of molecular dust and clouds in the cores of galaxies – an indicator of star formation activity.
The massive clusters of gas and dust in the galaxies concentrate star formation at the center of the galaxy. By using the European Southern Observatory's Very Large Telescope, the researchers confirmed that none of the galaxies' stellar bulges were a result of merger events.
"Here, we obtained firm evidence that dense galactic cores can be formed without galaxy collisions. They can also be formed by intense star formation in the heart of the galaxy," noted Tadaki. ®