Thursday, September 1, 2011

A star that is probably not

A star that is probably not

Guesswork about the oldest and most metal-poor star of all at the same
time (so far) cosmic times, the ESO astronomers recently discovered
Published today in the scientific journal "Nature" reported the team of
astronomers of the European Southern Observatory (ESO) in Chile from the
discovery of a stellar, highly durable loner, who, against all theory in
the interior hardly metals and mostly consists of hydrogen and helium.
According to the Stern model would also need to have a minimum
concentration of lithium - but he has not. Meanwhile, it looks to revise
astronomers as would some of their models of stellar formation. Further
observations should clarify how many bizarre stellar vagabond style of
this chemical in the universe are at home.


Stellar element factory
About a hundred million years after the Big Bang, still in the midst of
phase of galaxy formation, the first stars lit the young universe.
Consisting mainly of hydrogen and helium, this giant astral were unique
compared to our parent star much heavier and larger, so its interior
were held in the nuclear fusion processes faster and faster.
The pressure exerted by its own weight on the innermost regions of
Stern's pressed, the nuclei of hydrogen atoms so close together that
their merger was completed within a few million years to form helium.
And the pace has continued: the left for a short period-ending source of
energy inside the gravity of the star for only a short time free hand.
The star declined, the matter was again compressed and intensified even
more hotter.


In this heat the helium nuclei fused together and formed elements such
as carbon, oxygen and neon. Later, several elements have emerged in
several layers, but only when inside the star had enriched iron, this
process came to a halt. During her last stages of life produced the
archaic giants all stable heavy elements, gold and uranium last year.
Almost a pure hydrogen-helium star
No wonder then, that this type of star is still on the short-lived
stellar objects in the universe is one, but he clears his stellar fire
normally again after several million years.
That also in the primordial universe, at least ignited a chemically very
simply constructed stellar long-running has that ever since flooded the
universe with light, has recently signed a 15-strong European team of
astronomers with the installed at Cerro Paranal Very Large Telescope
(VLT) of the European Southern Observatory (ESO) in Chile found.

Digitized, multiple-frame shot of the approximately 600 light years
distant star Betelgeuse (and Betelgeuse), which has 662 times the
diameter of the sun and at least ten thousand times as large luminosity
in the visible range. Stars can be the best telescope can not resolve
detail - our sun is the Ausnahme.Bild: ESO / Digitized Sky Survey, 2nd
Acknowledgment: Davide De Martin.
With the 8.2-meter mirror Kueyen they localized in the constellation Leo
a faint star that has the characteristics that have kept many
researchers previously considered impossible.
Seen in that of the Earth from 4000 light years distant sun in the
unseemly Catalog SDSS J102915 is +172927 they are stellar member of the
Milky Way, which consists almost entirely of hydrogen (almost 75
percent) and helium (almost 25 percent) and few other chemical elements
in a remarkably small amount, has its value is only 0.0007 percent.
Of all the stars has been known of these celestial bodies whose mass is
slightly smaller than our Sun (about 0.8 solar masses), the lowest
proportion of elements on which are heavier than helium. All that is
heavier than helium call, astronomers commonly referred to as metals.


"Predicts a generally accepted theory is that a star that has a low mass
and very low concentration of metal, can not exist, because the dust
clouds from which he fashioned himself would like to never compacted,"
Elisabetta Caffau says of the Center for Astronomy at the University of
Heidelberg (ZAH, the lead author of the Nature contribution today
published "An extremely primitive halo star."
It was surprising to find a star for the first time in this, forbidden
zone '. It means that we need to rethink some of the models of stellar
formation.
20,000 times less iron than the Sun
The team examined the components of the star with the X-shooter and the
UVES spectrograph to the VLT, with which they could measure the
frequency of various chemical elements in the star. They found that the
metal content in SDSS J102915 +172927 whopping 20,000 times smaller than
our sun.

Without the arrow as a marker of the newly discovered star SDSS J102915
+172927 would barely notice. With the amateur telescope and even with
certain professional telescopes it would be impossible to locate. Image:
ESO / Digitized Sky Survey
To determine the small differences in the distribution of metals in the
star accurately, several observations were nonetheless necessary as the
project leader of the observation, Piercarlo Bonifacio, Observatoire de
Paris, confirms:
The star is so faint and metal-poor, that we were there at our first
observations only discovered the signature of a single element that is
heavier than helium: calcium. In order to observe the starlight detailed
with a longer exposure time, and find other metals, we had to ask the
Director General of ESO additional telescope time.
Against all theory is also the age of the star, which amounts to the
surprise of astronomers led by Caffau probably more than 13 billion
years. The astral fossil comes from the primordial universe, in its time
had the lightest elements of the substantive announcements. He continued
his approach in an interstellar environment in which there was the
matter of the very young universe to 75 percent to 25 percent of
hydrogen and helium, and some still bore traces of lithium.


All other heavy elements we know today were later (with the exception of
some man-made elements) over millions of stars formed in all. And as a
result of supernovae explosions evaporated then the star material in the
interstellar space, where the metal is enriched, and where new stars are
continually formed. Like this rose to everyone formation of a new star
of the metal content, the astronomers can now turn the age of a star.


50 times less lithium than expected
The formula for this is simple and effective: the higher the star
containing a metal concentration, the higher his age. SDSS J102915
+172927 But with the determination of the age would be based solely on
this not very productive, as confirmed by Lorenzo Monaco observation
team of ESO.
The star we have studied is very primitive and extremely metal
structure. He could be one of the oldest stars we have ever found.
Were no less surprised the researchers also measured the extremely low
percentage of SDSS J102915 +172927 in lithium. According to one model of
such old star would have to have those chemical composition, which has
coined shortly after the Big Bang, the chemistry of the universe. But in
fact, the lithium concentration fell from fifty times lower than
expected. "For us it's a mystery how this star that has consumed
immediately after the Big Bang formed lithium," says Piercarlo Bonifacio.

The ESO VLT at Cerro Paranal. Image: ESO
Other candidates in the focus
Since ESO scientists in 2005 with the VLT a very metal-poor star HE
1327-2326, called tracking down who had the lowest concentration of iron
until then, but it was very rich in carbon, discovered in 2007 and even
a 13.2 billion years old star ] wants to keep another team after
Bonifacio's brothers and sisters of SDSS J102915 +172927 lookout.
Finally, the newly discovered star Caffaus view, not be a cosmic loner.
There are many indications that he is not alone in the universe.

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