Our solar system lies within the Milky Way whose name is derived from its appearance when seen from the Earth which is a cloudy collection of visible at night because it is composed of numerous stars which not distinguishable without the aid of powerful space telescope. In 1610 Galileo said that the band of light as it is seen from the Earth was actually made of individual stars and after the early 1920s it was widely believed that it contains all the staler objects in the universe.
However, after the 1920s, it was discovered that the Milky Way is just one among the several galaxies that exist in our universe. The galaxy is estimated to have a diameter of between 150,000 and 200,000 light years. The solar system is estimated to lie at a radius of about 26,490 light years from the galactic center in the Milky Way. Some of the common elements in the Milky Way galaxy include hydrogen, helium, oxygen, carbon, and others.
Hydrogen is by far the universe’s most abundant element. It accounts for about 75% of the baryonic mass in the universe. Most of the non-remnant stars are primarily made up of hydrogen, particularly in a plasma state. Diatomic hydrogen appeared in the universe during the recombination or Big Bang epoch. Hydrogen in its standard pressure and temperature is odorless, colorless, tasteless, non-metallic, non-toxic, and highly combustible. Hydrogen found in the universe is not in the form of the chemical-element type, but it is believed to occur in undetected forms such as dark energy and dark matter. Hydrogen is the most abundant in the Milky Way galaxy and our solar system. Most stars have hydrogen in abundance, and it is the element that powers the stars through the CNO and Proton-to-proton reaction of nuclear fusion. Hydrogen in the universe is mainly in the state of plasma or atomic having properties which are relatively unlike the molecular hydrogen. Hydrogen in plasma state has protons and electrons which are not bonded and therefore, they have a high conductivity of electrical an extremely high emissivity, which gives the stars like our sun the property to emit light.
Helium is an odorless, colorless, tasteless, monoatomic, and non-toxic gas. It is the universe’s second most plentiful element and by far the lightest element. Helium accounts for 25% of all the atoms in the universe and most of it were created during the Big Bang nucleosynthesis, and it is known as primordial helium, but colossal amounts of the gas is created almost daily through nuclear fusion of hydrogen in the stars. The element has two neutrons and two protons surrounded by two electrons. The most abundant type of helium in the universe is helium-4, which is a non-radioactive isotope of the helium element. Primordial helium-4 is largely not found in the Earth, because it is believed to have escaped during the high-temperature stage of the Earth’s formation. The helium-4 found on Earth is a result of radioactive decay of other elements, which were produced after the Earth solidified and cooled.
Oxygen is a nonmetal, reactive, chemical element, and it is an oxidizing agent as well, which reacts with most elements or other compounds to form oxides. It is the universe’s 3rd most plentiful element. Two atoms of oxygen under standard pressure and temperature would form one of the allotropes of oxygen known as dioxygen or diatomic oxygen, which is an odorless and colorless gas. The halo or the corona of the Milky Way galaxy is believed to host extremely hot ionized oxygen, which is thought to have been blasted by the exploding supernovas or stars in the galaxy. According to the NASA’s satellite in 2000, it captured images of super hot oxygen cloud widely distributed irregularly along the Milky Way, and it is believed to extend in all directions covering a distance of between 5,000 and 10,000 light years away from the plane of the galaxy. The region is part of the Milky Way where stars and other staler object are found.
Carbon is a chemical element having an atomic number of 6, which is tetravalent and nonmetallic. Carbon-12 and carbon-13 are three isotopes of carbon occurring naturally and are stable, but carbon-14, which is another isotope, is radionuclide having half-life decay of approximately 5,730 years. There are four electrons existing in carbon element available to form chemical bonds and covalent. Carbon is among the elements which have been known from antiquity and it the 15th most plentiful in the crust our planet Earth and the 4th most plentiful in the universe. NASA has been tracking and following polycyclic aromatic hydrocarbons (PAHs), and in 2014, it announced that it had upgraded its database on PAHs. It is estimated that the universe is composed of more than 20% carbon mainly associated with PAHs, which is a complex compound of carbon and hydrogen and does not contain oxygen. The combination of these elements has been used in the PAH hypothesis, which is believed to have played a significant role in abiogenesis and the formation of life. The thought PAH may have been formed several billions of years following the Big Bang, and they are widely found throughout the universe which has led to the belief that they are responsible for the formation of new stars and exoplanets.
Contents of the Milky Way Galaxy
According to astronomers, the Milky Way galaxy host stars ranging from 200 billion to 400 billion and at least 100 billion planets. The nearest galaxy Andromeda Galaxy is believed to have about one trillion stars and planets. It is also believed that the Milky Way galaxy hosts about ten billion white dwarfs and one billion neutron stars. It is also thought to have about 100 million black holes. The spaces between the stars are filled with a disc of dust and gas, which is known as the interstellar medium, which has a comparable radius to that of the stars. The thickness of the dust layer lies between hundreds of light-years for a cooler gas and thousands of light-years for hotter gas.