There are stars in the sky. Our own sun is one of billions of them in the Milky Way. Billions of galaxies are in the universe. We have learned that hundreds of stars have planets.
A star develops from a giant, slowly rotating cloud that is made up entirely or almost entirely of hydrogen and helium. Due to its own pull, the cloud begins to collapse inward, and as it shrinks, it spins more and more quickly, with the outer parts becoming a disk while the innermost parts become a spherical clump.
This material forms a ball-shaped protostar when it grows hotter and denser. The star ignites when the heat in the protostar reaches about 1 million degrees Celsius. Nuclear fusion converts a small amount of the mass of these atoms into extraordinary amounts of energy.
The life cycles of stars are based on their initial mass. Intermediate-mass stars such as the sun, with half to eight times the mass of the sun, high-mass stars that are more than eight solar mass, and low-mass stars are included. According to NASA, the lifespan of stars with greater mass is shorter. Nuclear fusion can't happen with objects smaller than a tenth of a solar mass.
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An intermediate-mass star begins with a cloud that takes 100,000 years to collapse into a protostar with a surface temperature of 6,750 degrees F. A variable star that fluctuates in brightness is the result of hydrogen fusion. After 10 million years of collapsing due to energy generated by nuclear fusion, the star becomes a main-sequence star that gets all its energy from hydrogen fusion in its core.
The bigger the star, the quicker it will use its hydrogen fuel and the shorter it will stay on the main sequence. After the hydrogen in the core is fused into helium, the star changes rapidly, without nuclear radiation to resist it, gravity immediately crushes matter down into the star's core, heating the star. The star's outer layers expand enormously and to cool and glow red as they do so, rendering it a red giant.
The core of the star becomes hotter once the helium is gone and it becomes bluer and brighter than before. The white dwarf is made of mostly carbon and oxygen with an initial temperature of 180,000 degrees F. White dwarfs have no fuel left for fusion, so they grow cooler and cooler over billions of years to become black dwarfs. Our sun should leave the main sequence in about 5 billion years.
A star forms and dies quickly. These stars were formed from the beginning of the universe in 100,000 to 10,000 years. They are hot and blue and are 10 times wider than the sun. When they leave the main sequence, they become a bright red supergiant and become hot enough to make carbon heavier. After 10,000 years of fusion, the result is an iron core roughly 3,800 miles wide, and since any more fusion would consume energy instead of freeing it, the star is doomed, as its nuclear radiation can no longer resist the force of gravity.
When a star reaches a mass of more than a solar mass, the pressure on the core can't support it. The result is a big bang. The core temperature rises to nearly 18 billion degrees F (10 billion degrees C) when gravity causes it to collapse. In about one second, the core shrinks to about 10 km wide and breaks in two, sending a shock wave through the star that causes fusion to occur in the outlying layers. The star explodes in a type II supernova. If the stellar core was less than three solar masses large, it becomes a neutron star made up almost entirely of neutrons, and rotating neutron stars that beam out radio waves are known as pulsars. If the stellar core was larger than three solar mass, no known force can support it against its own pull, and it collapses to form a black hole.
Since the universe is only about 13 billion years old, a low-mass star using hydrogen fuel can shine as a main-sequence star for 100 billion to 1 trillion years. Red dwarfs will never become red giants because they will never fusion with anything but hydrogen. They should become white dwarfs and then black dwarfs.
According to the International Astronomical Union, stars have been vital to navigation since the dawn of recorded civilization. The study of the heavens may be the most ancient of the sciences. The discovery of the laws of motion and gravity in the 17th century led to the realization that stars were just like the sun, obeying the same laws of physics. In the 19th century, the study of the wavelengths of light that objects emit made it possible to investigate the compositions and motions of stars from afar.
The first radio telescope was built in 1937. The first telescope to study star explosions was launched in 1961. Astronomers began using balloon-borne telescopes in the 1960s to gather information about stars and other objects based on their heat emissions, and the firstInfrared Telescope was launched in 1983.
The first study of microwave emissions from space was done in 1992. Microwave emissions can be used to probe the young universe's origins, but they can also be used to study stars. The Hubble Space Telescope was launched in 1990 to provide the deepest, most detailed view of the universe.
Over the years there have been more advanced observatories, and even more powerful ones are planned. The ELT is planned to start observations in the year 2024, and is one of a few examples. The James Webb Space Telescope will be used to probe stars in theIR.
Ancient cultures saw patterns in the heavens that resembled people, animals or common objects, and so they created constellations to represent figures from myth.
constellations are used in the naming of stars. 88 constellations are officially recognized by the International Astronomical Union. The first letter of the Greek alphabet is part of the scientific name of the bright star in a constellation. When all the Greek letters are used, the second brightest star in a constellation is usually designated "beta", the third "gamma" and so on.
A number of stars have been called Betelgeuse since antiquity. The scientific name of the star is Alpha Orionis. Different astronomer have compiled star catalogs that use different numbering systems. The Henry Draper Catalog has been used by the astronomy community for over half a century. Betelgeuse is designated as HD 39801 in the catalog.
The IAU uses a different system for new stars since there are so many. The abbreviation stands for either the type of star or a catalog that lists information about the star, followed by a group of symbols. J1302-6350 is a pulsar. The coordinates 1302 and 6350 are similar to the latitude and longitude codes used on Earth, according to the J.
The public was included in the naming process of several stars in recent years. The IAU took suggestions from science and astronomy clubs around the world in order to create 14 star names for the contest.
In 2016 the IAU approved 227 star names. The goal was to reduce variations in star names and spelling. The name of the famous star system with planets just four light-years from Earth was replaced with Rigel Kentaurus.
Our solar system only has one star, but it's not the only star in the system. One-third of stars like our sun are single, while two-thirds are multiples, and the closest neighbor to our solar system, Proxima Centauri, is part of multiple systems.
Two stars form near each other. Mass transfer is a process in which one member of this pair can influence its companion. If one of the members is a giant star that leaves behind a black hole, an X-ray binaries can form, where the companion can get very hot.
A nova can occur if gas pulled from a companion onto a white dwarf is thrown into the sky. When enough gas builds up for the dwarf to collapse, the dwarf's carbon will explode in a Type I supernova, which can take months to complete.
There is a high amount of brightness.
The magnitude and luminosity of stars are described by Astronomers.
The magnitude of a star is based on a scale more than 2,000 years old, devised by Greek astronomer Hipparchus around 125 BC, according to NASA. The stars were numbered based on their brightness as seen from Earth, with the first magnitude stars, the second magnitude, and the faintest visible ones.
Astronomers refer to a star as its apparent magnitude, but since the distance between Earth and the star can affect the light one sees from it, they now also describe the actual brightness of a star using the term absolute magnitude. The magnitude scale runs to more than six and less than one, even descending into negative numbers, and the bright star in the night sky is Sirius with an apparent magnitude of -1.46.
The rate at which a star emits energy is called luminosity. The sun's luminosity is 400 trillion trillion watt and is usually measured in terms of the star's luminosity. Alpha Centauri A is 1.3 times as bright as the sun. A star with an absolute magnitude of 1 is 100 times more Luminous than a star with an absolute magnitude of 5.
The surface temperature and size of a star have an effect on its brightness.
There is a color.
Stars are in a range of colors. A star's color depends on its surface temperature.
A star might appear to have a single color, but actually emits a broad spectrum of colors, including radio waves and IR rays. By studying a star's spectrum, one can divine what its composition might be, as different elements or compounds absorb and emit different colors or wavelength of light.
The surface temperature.
Astronomers measure the star's temperature in a unit known as the kelvin, which is minus 273.15 degrees C or minus 459.67 degrees F.
The surface temperature of a star depends on its mass and how bright it is. The star's luminosity is determined by the temperature of the fourth power. If two stars are the same size but one is hotter, the latter would be 16 times as bright as the other.
How hot is the sun?
There is a size.
Astronomers measure the size of stars by the radius of the sun. Alpha Centauri A has a radius of 1.05. The stars range in size from small to large, with some being 1,000 times the diameter of the sun.
A star's brightness is affected by its size. The luminosity is related to the radius squared. If one star was twice as wide as the other, the latter would be four times as bright.
Mass.
The mass of our sun is represented by the solar mass, which is the mass of a star. Alpha Centauri A is 1.08 solar mass.
Stars with different densities might be different in size. The mass of the sun is roughly the same as that of the B, but it's dense and only a fiftieth of its diameter.
The surface temperature is affected by the mass of a star.
There is a magnetic field.
Magnetic fields are generated by stars spinning balls of charged gas. The sun's magnetic field can become highly concentrated in small areas, creating features such as sunspots and flares. The Harvard-Smithsonian Center for Astrophysics found that the stellar magnetic field increases with the star's rate of rotation and decreases as it ages.
There is metallicity.
The metallicity of a star is the amount of metal it has.
Three generations of stars may be based on metallicity. Population II stars released heavy elements into the universe when they died, but they have not yet been discovered. Heavy elements were released when a number of these died, and the youngest Population I stars like our sun have the largest amounts of heavy elements.
According to the European Southern Observatory, stars are classified by their spectrum in the Morgan-Keenan system. There are eight classes, each similar to a range of surface temperatures, ranging from the hottest to the lowest.
Under the Morgan-Keenan system, stars are classified by their luminosity. Ia is a bright supergiant, Ib is a supergiant, II is a bright giant, III is a giant, and IV is a subgiant.
For instance, the sun is a G2V.
The structure of a star can be thought of as a series of thin nested shells.
A main-sequence star consists of a core, radiative and convective zones, a photoosphere, and a corona. Nuclear fusion takes place in the core.
In the radiative zone, the energy from the reactions is taken out by radiation, like heat from a light bulb, while in the convective zone, the energy is taken out by hot gases. Massive stars that are more than several times the mass of the sun are convective in their core and radiative in their outer layers, while stars comparable to the sun or less in mass are radiative in their core and outer layers. Intermediate-mass stars of type A may be radiative.
The surface of the star is referred to as the photoosphere after those zones. There is a reddish layer after that because of all the hydrogen found there. The corona is the part of the atmosphere that is super-hot.
NASA has a Skymap tool that you can use to explore the stars of our universe. The European Space Agency has an archive of images taken by the Hubble Space Telescope.
The evolution of stars and stellar populations was studied. John Wiley and Sons are on the internet.
Thetral classification The Annual Review of Astronomy and Astrophysics was published in 1973.
The Star Formation Cycle in Nearby Star-forming Galaxies is known as the Gas. The Astrophysical Journal published an assessment of multi-scale variations.
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