CZECH REPUBLIC: 26th International Astronomical Union General Assembly discusses developments in the field

Almost 3000 astronomers from around the world are meeting in Prague for the 26th International Astronomical Union General Assembly to discuss developments in the field. The team of Dr. Harvey Richer and Dr. Gregory Fahlman published the results of their project: "Probing the Faintest Stars in a Globular Star Cluster" in the observed field NGC 6397. NGC 6397 is the second closest globular star cluster to the Sun. Using the NASA/ESA Hubble Space Telescope for 5 days they have constructed the deepest ever colour-magnitude diagram for this cluster. They have discovered the lowest-mass stars capable of supporting stable nuclear reaction in this cluster. Any less massive ones faded early in the cluster's history and by now are too faint to be observed. "If you look at the star cluster. All the stars in the star cluster will move together across the sky," said Dr. Gregory Fahlman during the presser at Prague Congress Centre. "These stars are a big balls of gas, is what they are. And they have to be big enough in order to undergo the nuclear reactions that keep the star hot. The question has always been how big is big enough for a ball of gas to become a star. The answer has been known for quite a while, at least people have thought they know the answer for quite a while - it's about 8 per cent of the mass of the sun. Anything bigger will shine, anything fainter, anything smaller, will not shine as a star." Dr. Harvey Richer explained the conclusions of the project: "What we have found is that the end of the two major stellar sequences, the stars which are burning hydrogen in their core, which provides their energy and the group of burntout stars called white dwarfs and they have cooled to very, very cool temperatures and we have found the truncation in that sequence also. The first one tells us, what are the lowest mass stars that can actually burn hydrogen. The second one tells us how old the cluster is, how faint can these stars cool to over the lifetime of the cluster. And it's a very good diagnostic for the age of the cluster." The Astronomers Congress in Prague continues until August 25 during which time the astronomers will publish their new decision about whether or not Pluto is a planet.

ITN Source | August 18, 2006

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