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Some stars may once have been more massive than they are today. It is likely that many large stars have suffered significant mass loss (perhaps as much as several tens of solar masses). This mass may have been expelled by superwinds: high velocity winds that are driven by the hot photosphere into interstellar space. The process forms an ...
It is known that small planets (of roughly Earth-like mass or slightly larger) are more common than giant planets. [6] It also appears that there are more planets in large orbits than in small orbits. Based on this, it is estimated that about 20% of Sun-like stars have at least one giant planet, whereas at least 40% may have planets of lower mass.
The coolest of these, 2MASS J10475385+2124234 with a temperature of 800-900 K, retains a magnetic field stronger than 1.7 kG, making it some 3000 times stronger than the Earth's magnetic field. [18] Radio observations also suggest that their magnetic fields periodically change their orientation, similar to the Sun during the solar cycle .
These magnetic fields are a hundred million times stronger than any man-made magnet, [11] and about a trillion times more powerful than the field surrounding Earth. [12] Earth has a geomagnetic field of 30–60 microteslas, and a neodymium-based, rare-earth magnet has a field of about 1.25 tesla, with a magnetic energy density of 4.0 × 10 5 J ...
A typical large galaxy like the Milky Way contains hundreds of billions of stars. There are more than 2 trillion (10 12) galaxies, though most are less than 10% the mass of the Milky Way. [107] Overall, there are likely to be between 10 22 and 10 24 stars [108] [109] (more stars than all the grains of sand on planet Earth).
The stars with the most confirmed planets are the Sun (the Solar System's star) and Kepler-90, with 8 confirmed planets each, followed by TRAPPIST-1 with 7 planets. The 1,033 multiplanetary systems are listed below according to the star's distance from Earth. Proxima Centauri, the closest star to the Solar System, has three planets (b, c and d).
The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapse supernovae; [102] while smaller stars blow off their outer layers and leave behind the inert core in the form of a white dwarf. The ejection of the outer layers forms a planetary nebula. [103]
Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right Chart of stellar evolution