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Abundance of Elements in Milky Way
Our home galaxy, Milky Way galaxy, with its stellar disk approximately 100,000 ly (light years) in diameter and 1000 ly in thickness, is estimated to contain 100-400 billion stars, 10 billion white dwarfs, one billion neutron stars, 100 million black holes, at least as many planets bound to stars as there are stars, more rogue planets not bound to host stars than there are stars (It is interesting to know that even with these huge numbers, Milky Way galaxy loses the competition to the nearby Andromeda galaxy located at 2.5 million light years from earth where the neighboring Andromeda galaxy is estimated to contain one trillion (10^12) stars!!).
Milky Way is massive, a low estimate of its mass is about 6×10^11 solar masses (the solar mass is the mass of the Sun, approximately equal to 2×10^30 kg). Much of the mass of the Milky Way appears to be dark matter, an unknown and invisible form of matter that interacts gravitationally with ordinary matter. The total mass of all the stars in the Milky Way is estimated to be about 5×10^10 solar masses, in addition to the stars, there is also interstellar gas and dust, the matter that exists in the space between the star systems in a galaxy, and the mass of this interstellar matter is about 10-15% of the total mass of the galaxy’s stars.
While stars like sun, interstellar gas and dust, planets … are made of standard (baryonic) matter in the form of atoms or ions (plasma), other astronomical bodies like neutron stars and black holes have different situations. Spectroscopic methods have been a powerful tool for study of the universe from many aspects like determination of abundance of elements.
(Numbers are from the Wikipedia article “Milky Way”, for more information see: https://en.wikipedia.org/wiki/Milky_Way)
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