Missing primitive stars outside Milky Way uncovered

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Munich, Feb 18 (ANI): New observations using ESO's (European Southern Observatory's) Very Large Telescope have uncovered the missing primitive stars outside the Milky Way galaxy.

"We have, in effect, found a flaw in the forensic methods used until now," says Else Starkenburg, lead author of the paper reporting the study.

"Our improved approach allows us to uncover the primitive stars hidden among all the other, more common stars," Starkenburg added.rimitive stars are thought to have formed from material forged shortly after the Big Bang, 13.7 billion years ago.

They typically have less than one thousandth the amount of chemical elements heavier than hydrogen and helium found in the Sun and are called "extremely metal-poor stars".

They belong to one of the first generations of stars in the nearby Universe. Such stars are extremely rare and mainly observed in the Milky Way.

Cosmologists think that larger galaxies like the Milky Way formed from the merger of smaller galaxies.

Our Milky Way's population of extremely metal-poor or "primitive" stars should already have been present in the dwarf galaxies from which it formed, and similar populations should be present in other dwarf galaxies.

"So far, evidence for them has been scarce. Large surveys conducted in the last few years kept showing that the most ancient populations of stars in the Milky Way and dwarf galaxies did not match, which was not at all expected from cosmological models," said co-author Giuseppina Battaglia.

Element abundances are measured from spectra, which provide the chemical fingerprints of stars.

The Dwarf galaxies Abundances and Radial-velocities Team used the FLAMES instrument on ESO's Very Large Telescope to measure the spectra of over 2000 individual giant stars in four of our galactic neighbours, the Fornax, Sculptor, Sextans and Carina dwarf galaxies.

Since the dwarf galaxies are typically 300 000 light years away - which is about three times the size of our Milky Way - only strong features in the spectrum could be measured, like a vague, smeared fingerprint.

The team found that none of their large collection of spectral fingerprints actually seemed to belong to the class of stars they were after, the rare, extremely metal-poor stars found in the Milky Way.

The team of astronomers around Starkenburg has now shed new light on the problem through careful comparison of spectra to computer-based models.

They found that only subtle differences distinguish the chemical fingerprint of a normal metal-poor star from that of an extremely metal-poor star, explaining why previous methods did not succeed in making the identification. (ANI)

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