بسم الله
Looking at the chemical composition of stars that host planets, astronomers have found that while dwarf stars often show iron enrichment on their surface, giant stars do not
they think that the planetary debris falling onto the outer layer of the star produces a detectable effect in a dwarf star, but this pollution is diluted by the giant star and mixed into its interior
planets are preferentially found around stars that are enriched in iron
Planet-hosting stars are on average almost twice as rich in metals than their counterparts with no planetary system
chicken and egg paradox
whether
this richness in metals enhances planet formation
or
it is caused by the presence of planets
من خلق اولا ؟ : الدجاجه ام البيضه
البيضه اصلها دجاجه ، والدجاجه اصلها بيضه
سبحان الله
in first case
the stars would be metal-rich down to their centre.
second case
debris from the planetary system would have polluted the star and only the external layers would be affected by this pollution
by observing stars and take spectra
astronomers indeed only see the outer layers and can't make sure the whole star has the same composition
When planetary debris fall onto a star, the material will stay in the outer parts, polluting it and leaving traces in the spectra taken
A team of astronomers has decided to takc this question by looking at a different kind of stars
Looking at the distribution of metals in fourteen planet-hosting giants, the astronomers found that their distribution was rather different from normal planet-hosting stars
red gaints
have exhausted the hydrogen in their core
and so they have puffed up, becoming much larger and cooler
the sun will do this after several billion years
Looking at the various options, the astronomers conclude that the most likely explanation lies in the difference in the structure between red giants
and solar-like stars
convective zone is only 2% of star mass like sun
the region where all the gas is completely mixed
but for red gaints is huge
encompassing 35 times more mass than the star
The polluting material would thus be 35 times more diluted in a red giant than in a solar-like star
solar-like stars appear metal-rich because of the pollution of their atmospheres
When the star was still surrounded by a proto-planetary disc, material enriched in more heavy elements would fall onto the star, thereby polluting its surface. The metal excess produced by this pollution, while visible in the thin atmospheres of solar-like stars, is completely diluted in the extended, massive atmospheres of the giants
source
european south telescope
eso
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