Today.Az » Weird / Interesting » The star that should not exist
01 September 2011 [19:40] - Today.Az
A faint star in the constellation of Leo (The Lion), called SDSS J102915+172927 [1], has been found to have the lowest amount of elements heavier than helium (what astronomers call "metals") of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.
"A widely accepted theory predicts that stars like this, with low
mass and extremely low quantities of metals, shouldn't exist because the
clouds of material from which they formed could never have condensed,"
[2] said Elisabetta Caffau (Zentrum fur Astronomie der Universitat
Heidelberg, Germany and Observatoire de Paris, France), lead author of
the paper. "It was surprising to find, for the first time, a star in
this 'forbidden zone', and it means we may have to revisit some of the
star formation models."
The team analysed the properties of the star using the X-shooter and
UVES instruments on the VLT [3]. This allowed them to measure how
abundant the various chemical elements were in the star. They found that
the proportion of metals in SDSS J102915+172927 is more than 20 000
times smaller than that of the Sun [4][5].
"The star is faint, and so metal-poor that we could only detect the
signature of one element heavier than helium -- calcium -- in our first
observations," said Piercarlo Bonifacio (Observatoire de Paris, France),
who supervised the project. "We had to ask for additional telescope
time from ESO's Director General to study the star's light in even more
detail, and with a long exposure time, to try to find other metals."
Cosmologists believe that the lightest chemical elements -- hydrogen
and helium -- were created shortly after the Big Bang, together with
some lithium [6], while almost all other elements were formed later in
stars. Supernova explosions spread the stellar material into the
interstellar medium, making it richer in metals. New stars form from
this enriched medium so they have higher amounts of metals in their
composition than the older stars. Therefore, the proportion of metals in
a star tells us how old it is.
"The star we have studied is extremely metal-poor, meaning it is very
primitive. It could be one of the oldest stars ever found," adds
Lorenzo Monaco (ESO, Chile), also involved in the study.
Also very surprising was the lack of lithium in SDSS J102915+172927.
Such an old star should have a composition similar to that of the
Universe shortly after the Big Bang, with a few more metals in it. But
the team found that the proportion of lithium in the star was at least
fifty times less than expected in the material produced by the Big Bang.
"It is a mystery how the lithium that formed just after the beginning
of the Universe was destroyed in this star." Bonifacio added.
The researchers also point out that this freakish star is probably
not unique. "We have identified several more candidate stars that might
have metal levels similar to, or even lower than, those in SDSS
J102915+172927. We are now planning to observe them with the VLT to see
if this is the case," concludes Caffau.
/Science Daily/
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