Astronomers plan search for rare stars

Astronomers using the large MMTO telescope on nearby Mount Hopkins plan to use it later this year to search for rare Wolf-Rayet stars as Gamma-ray sources in our Milky Way galaxy.

Grant Williams, a Mount Hopkins astronomer, told about 230 people Tuesday about the expanded look for Wolf-Rayet, or WR, stars relatively close to home, in our own galaxy.

Williams has done work using a smaller University of Arizona telescope housed on Kitt Peak, but he wants to find more WR stars, hence the use of the much larger MMTO telescope.

The main mirror in the MMTO is 6.5 meters across or about 21 feet.

Williams at one of the Smithsonian Institution’s periodic lectures here, said WR stars are the “genesis of Gamma-ray bursts.”

Gamma-rays are extremely powerful, but fortunately the Earth’s upper atmosphere can destroy them,

Their collision with the atmosphere produces a faint, bluish light called Cherenkov’s light.

Williams said there are about 230 WR stars in our Milky Way galaxy.

With the Kitt Peak instrument he and colleagues have surveyed 18 new WR stars.

WR stars are named for discoverers Charles Wolf and Georges Rayet, who first reported them in 1867 at the Paris Observatory.

WR stars “end their lives as black holes,” said Williams, when much of the matter has been ejected and they collapse into a seemingly bottomless pits where neither light nor energy can escape.

This kind of end game is when long bursts of Gamma-rays occur.

Earlier in their lives, WR stars are noted for shedding much of their mass through very strong stellar winds.

Our nearest star, the sun, sheds some of its mass through stellar winds, but that of WR stars is many, many times greater.

The MMTO started its life as the Multiple Mirror Telescope, using six mirrors to collect the light.

It has been rebuilt with the single mirror and although there is no more multiple mirror telescope the observatory retains the MMTO.

The next lecture in the Smithsonian’s “New Vistas in Astronomy” series will be 9 a.m. Tuesday, Feb. 26, at the West Center.

Astronomer Emilio Falco of the Whipple Observatory will talk about “Strange new planets.”

There’s no admission charge.

jlamb@gvnews.com | 547-9749