Supernovae workshop to explore theories related to expansion

Two independent research groups created a sensation early this year when-using exploding stars from the most distant reaches of space as astronomical measuring devices-they separately presented evidence that the universe will expand forever.

But according to Jens Niemeyer, the Enrico Fermi Fellow at the University's Enrico Fermi Institute, these findings could backfire on the astronomical community. Because the physics of exploding stars are not yet fully understood, can they really be used to foretell the ultimate fate of the universe? An international group of astronomers will attempt to answer that question during a workshop about Type Ia Supernovae Theory taking place from Thursday, Oct. 29, to Saturday, Oct. 31, at the University.

Type Ia supernovae are believed to be thermonuclear explosions of white dwarfs, which are compact stars whose nuclear fuel has been exhausted. "The explosion is a complete disruption of the white dwarf. There's no compact remnant, no neutron star or anything left over," said Niemeyer.

Some white dwarfs exist in binary systems consisting of two stars. The white dwarf draws mass from its binary companion until it reaches a critical size. The heat intensifies, igniting a thermonuclear explosion that blasts the white dwarf to bits.

These explosions shine so brightly-and with such predictable brightness that they are known as standard candles-that astronomers use them as astronomical measuring devices to help determine the expansion rate of the universe. Theoretically, by comparing a type Ia supernovae at the edge of the known universe to similar ones nearby, scientists can estimate whether the universe will expand forever or eventually collapse back into itself under the force of gravity.

Workshop organizers Niemeyer and James Truran, Professor in Astronomy & Astrophysics, are members of a Chicago research group that specializes in the physics of type Ia supernovae.

"We will focus on how little or how much we understand of the explosions themselves in order to get a better feeling for their use as standard candles," Niemeyer said.

About 80 scientists are expected to attend the workshop, including representatives of the research groups whose findings triggered the meeting. Speakers will include Saul Perlmutter of the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory in California and Alex Filippenko of the international High-Z Supernova Search Team.

Both groups separately announced early this year that the expansion rate of the universe was not what most astronomers assumed it was. Most astronomers have assumed that a force called the cosmological constant has a value of zero. The latest supernovae findings suggest that the cosmological constant has a small but significant value, enough to measurably affect the expansion rate of the universe.

According to Einstein's 1917 therory of general relativity, the universe should be expanding. He introduced the concept of the cosmological constant into his equations to account for a steady-state universe because at the time, astronomers did not know the universe was expanding.

Following Edwin Hubble's discovery in 1929 that the universe does indeed expand, Einstein recanted his cosmological constant, calling it his greatest scientific mistake.