The most likely places where stars and planetary systems are forming in the universe are in nebulae composed of gas and dust.
Stars are massive, hot, luminous bodies of gas that emit large amounts of radiation and derive their energy from nuclear fusion. A planetary system comprises of a star and all the objects that revolve around it.
Stars are born in nebulae. They are a cluster of gas and dust scattered throughout a galaxy. Gravitational attraction between the gas and dust particles causes turbulence, which gives rise to knots. When these knots acquire sufficient mass, they collapse, and when the reach a certain temperature, nuclear fusion of hydrogen atoms into helium atoms begins. At this point, star has been born.
Planets can be said to be formed as a by-product of star formation, through a process called accretion. Smaller objects stick together through gravity, forming bigger objects. Gravitational pull from the nearby star and the object's own momentum causes the object to revolve round the star. At this point, a planet has been born.
Thus, the most likely places where stars and planetary systems are forming in the universe are in nebulae composed of gas and dust.
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