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In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-dark) matter in the universe is either hydrogen or helium, and astronomers use the word "metals" as convenient shorthand for "all elements except hydrogen and helium".
Metallicity comparison: [Fe/H] - Ratio of Iron to Hydrogen. This is not an exact ratio, but rather a logarithmic representation of the ratio of a star's iron abundance compared to that of the Sun.
The diagram shows the iron abundance, [Fe/H], on the x-axis and the abundance of alpha process elements, [α/Fe], on the y-axis. The data from Wallerstein (1962) is shown as red circles on top of the 2020 public data from the large scale stellar spectroscopic surveys APOGEE (DR16) and GALAH (DR3).
The metallicity distribution function is an important concept in stellar and galactic evolution.It is a curve of what proportion of stars have a particular metallicity ([Fe/H], the relative abundance of iron and hydrogen) of a population of stars such as in a cluster or galaxy.
The average amount of heavier elements relative to hydrogen, known as metallicity in astronomy, ranges from a third to a half of the value in the sun. [1] [2] Studying the chemical composition of the ICMs as a function of radius has shown that cores of the galaxy clusters are more metal-rich than at larger radii. [2]
Gas drag slows the pebbles below the escape velocity of the massive body causing them to spiral toward and to be accreted by it. Pebble accretion may accelerate the formation of planets by a factor of 1000 compared to the accretion of planetesimals, allowing giant planets to form before the dissipation of the gas disk.
They have even weaker hydrogen lines than F, but along with the ionized metals, they have neutral metals. There is a prominent spike in the G band of CN molecules. Class G main-sequence stars make up about 7.5%, nearly one in thirteen, of the main-sequence stars in the solar neighborhood. There are 21 G-type stars within 10pc. [c] [11]
It is not just heavy metals which can be toxic; other metals (for example beryllium and lithium) can be toxic too. [267] Sleeping in a closed room with an electric fan running does not result in "fan death", as is widely believed in South Korea among older people. [268] [269] As of 2019 this belief was in decline. [270]