Why do stars twinkle?

Want to know about the formation of stars? Well, scientists have found that cosmic dust is a vital ingredient that shapes them.

Astronomers also said that is important for understanding how primordial diffuse gas clouds assemble themselves into full-blown galaxies.

Thanks to a combination of new observations and supercomputer simulations, including those conducted by Kravtsov and Nick Gnedin, physicist at Fermi National Accelerator Laboratory, researchers have explained why stars formed more slowly in the early history of the universe than they did much later.

"What it shows is that at early stages of evolution, galaxies were much less efficient in converting their gas into stars," said Kravtsov.

"Early on, galaxies didn''t have enough time to produce a lot of dust, and without dust it''s very difficult to form these stellar nurseries.

"They don't convert the gas as efficiently as galaxies today, which are already quite dusty," he said.

The star-formation process begins when interstellar gas clouds become increasingly dense. At some point the hydrogen and helium atoms start combining to form molecules in certain cold regions of these clouds. A hydrogen molecule forms when two hydrogen atoms join.

The Gnedin-Kravtsov model has also provided a natural explanation for why spiral galaxies predominately fill the sky today, and why small galaxies form stars slowly and inefficiently.

"We usually see very thin disks, and those types of systems are very difficult to form in galaxy-formation simulations," said Kravtsov.

That''s because astrophysicists have assumed that galaxies formed gradually through a series of collisions. The problem: simulations show that when galaxies merge, they form spheroidal structures that look more elliptical than spiral.

But early in the history of the universe, cosmic gas clouds were inefficient at making stars, so they collided before star formation occurred.

"Those types of mergers can create a thin disk," said Kravtsov.

The findings were published in The Astrophysical Journal.