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The Solar System [d] is the gravitationally bound system of the Sun and the objects that orbit it. [11] It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc .
The core of the Sun is considered to extend from the center to about 0.2 of the solar radius (139,000 km; 86,000 mi). [1] It is the hottest part of the Sun and of the Solar System . It has a density of 150,000 kg/m 3 (150 g/cm 3 ) at the center, and a temperature of 15 million kelvins (15 million degrees Celsius; 27 million degrees Fahrenheit).
The Sun is the star at the center of the Solar System. It is a massive, nearly perfect sphere of hot plasma , heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies.
The Sun is believed to be inside the Local Bubble, so the density in the solar neighborhood is only about 10 3 atoms/m 3. [114] Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium.
Sagittarius B2 (Sgr B2) is a giant molecular cloud of gas and dust that is located about 120 parsecs (390 ly) from the center of the Milky Way.This complex is the largest molecular cloud in the vicinity of the core and one of the largest in the galaxy, spanning a region about 45 parsecs (150 ly) across. [2]
The solar wind consists of particles (ionized atoms from the solar corona) and fields like the magnetic field that are produced from the Sun and stream out into space. Because the Sun rotates once approximately every 25 days, the heliospheric magnetic field [11] transported by the solar wind gets wrapped into a spiral.
For the Sun, the astrosphere and astropause are called the heliosphere and heliopause. Approximately 70% of the mass of the interstellar medium consists of lone hydrogen atoms; most of the remainder consists of helium atoms. This is enriched with trace amounts of heavier atoms formed through stellar nucleosynthesis.
The Solar System is located within a structure called the Local Bubble, a low-density region of the galactic interstellar medium. [5] Within this region is the Local Interstellar Cloud (LIC), an area of slightly higher hydrogen density. It is estimated that the Solar System entered the LIC within the past 10,000 years. [6]