THE LIFE CYCLE OF STARS - Montessori Training

When the hydrogen in the core of asupergiant star is exhausted, the radiationof light and heat from the core can nolonger support the outer layers. The outerlayers collapse in upon the core suddenlyand then rebound in a supernova explosion.The explosion sends the outer layers flyingoff into space at tremendous speed,releasing as much energy in seconds as thesun will release in its lifetime, while theremaining core is crushed down into anincredibly small remnant.variations in stars are often visible fromearth. Astronomers attribute thosevariations to each star’s size, the amount oflight radiated, its distance from the earth,and its color.The simplest measure of a star’s brightnessis its luminosity, a measure of the amountof light energy produced by a star.Temperature and size have the most effecton the luminosity of a star, and temperaturealso determines the color. The bigger a staris, the greater the temperature and pressurein the core, the more nucleosynthesisoccurs, the more light it will give off, andthe more blue-white it will be. The smallerand cooler a star is, the less light it will giveoff, and the more red it will be.Astronomers also compare the brightnessof stars against each other in two differentways:Supernova 1987AIf the original giant star was six to ten timesthe mass of the sun, the core collapses toform a neutron star, an extremely densestar approximately 12 mi (20 km) indiameter. If the original star was more thanten times the mass of the sun, the corecollapses to form a black hole, an objectapproximately 6–12 mi (10–20 km) indiameter whose gravity is so powerful thateven light cannot escape.In sum, stars come in many sizes andcolors, from tiny red dwarfs that barelyqualify as stars, to massive supergiants sobig and bright that they would make thesun look like a very dim light bulb if put sideby side. Despite how far away they are, the• Absolute magnitude compares thebrightness of stars as if viewed from thesame distance, so that a star’s absolutemagnitude is determined by its size andtemperature, not by how close it is to theearth.• Apparent magnitude compares thebrightness of stars when viewed from theearth, so that a star’s apparentmagnitude is determined by its absolutemagnitude or luminosity, its distance fromearth, and any obscuring interstellarmaterial, gas and dust between starsand the earth.Many different factors thus make a starappear more or less bright when seen fromthe earth. If two stars are an equal distancefrom the earth, the larger star will appear© NAMC - North American Montessori Center108