Stars {star} have different sizes and ages.
names
Famous stars are Aldebaran, Algol, Altair, Antares, Arcturus, Betelgeuse, Canopus, Capella, Deneb, Polaris or North Star, Pollux, Procyon, Regulus, Rigel, Sirius, Spica, and Vega. Sirius or Dog Star is brightest star. Six-star groups {Pleiades} can be in winter sky. Sky can have star clusters {Hyades}.
nearby stars
Nearest star is dwarf star Proxima Centauri, at 4.2 light years. The class-G star Alpha Centauri is at 4.3 light-years. Nearest single class-G star with possible life is Tau Ceti, at 11.2 light-years. The nearest stars lie in five general directions away from Earth.
planet
20% of stars have planets, typically one or two times Jupiter size.
first stars
The first stars formed 100,000,000 years after universe origin. They were 100 to 1000 times more massive than Sun. They were 4 to 14 times wider. They were 1 to 20 million times brighter. They had surface temperature 100,000 K. They lasted only 3 million years, forming big black holes.
first stars: reionization
Light from first stars ionized hydrogen and helium {reionization} and caused 5% to 17% of CMB.
The 250 Chinese constellations {asterism} have five or six stars each.
Young star spouts material from both poles {bipolar outflow}.
Some red-giant stars have mass less than 1.25 Sun mass {Chandrasekhar limit}.
Major constellations {constellation}| are Andromeda, Bootes, Canis Major, Cassiopeia, Draco, Hercules, Orion, Pegasus, Perseus, Ursa Major or Great Bear, and Ursa Minor or Little Bear.
Dense and visible ionized-hydrogen spheres {HII region} {emission nebula}, at 5000 K to 20000 K, can be around blue-white stars.
After formation, star masses correlate with other star properties {Main Sequence}. Main-Sequence stars have mass and brightness that depend on surface temperature, which determines color. 98% of stars are on Main Sequence.
types
Giant blue stars are 30,000 K at surface, have masses 60 times Sun mass, last 10^8 years, are in class O, and have strongly ionized gases.
Blue-white stars are 20,000 K at surface, last 10^8 years, are in class B, have much neutral helium, and are 10% of stars.
White stars are 11,000 K at surface, are in class A, and are predominantly hydrogen.
Yellow-white stars are 7800 K at surface, are in class F, and have hydrogen decreasing and metals increasing.
Yellow stars are 6700 K at surface, are in class G, and have metals predominant.
Yellow-orange stars are 5600 K at surface and last 10^10 years.
Orange stars are 4500 K at surface, are in class K, and metals surpass hydrogen.
Red stars are 3400 K at surface, are 0.1 Sun mass, last 10^11 years, are in class M, have titanium oxide, and have weak violet light.
1% of stars are fainter than class M stars: class W, class R, class N, and class S.
lifetimes
Large stars live shorter, because they burn faster.
rotation
Main-Sequence stars rotate every 4 hours to 30 days. Bigger stars spin faster.
evolution
Over time, Main-Sequence stars increase diameter by 30% and double brightness, but surface temperature and mass stay constant. Stars accumulate helium at center, as nuclear fusion turns hydrogen into helium.
large stars
Large stars can be 40 to 120 times more massive than Sun, such as Pistol Star and LBV 1806-20. Stars cannot be larger, because higher temperature blows gases away faster.
At red-giant-phase end, stars with less than eight solar masses blow away outer layers {planetary nebula}|, at 10 km/s increasing to 1000 km/s, during 100,000 to 1,000,000 years. Gas rings fluoresce by ultraviolet light from remaining hotter star layers. Magnetic fields and companion stars shape planetary nebulae. Faster winds can push into slower winds to make gas rings {interacting stellar winds hypothesis}, but most nebula do not follow this model. Planetary nebula include Ant, Blue Snowball, Bug, Calabash, Cat's Eye, Dandelion Puff Ball, Egg, Hubble's Double Bubble, Red Rectangle, Ring, Southern Crab, Stingray, Starfish twins, and Twin Jet.
RR Lyrae variable stars and blue horizontal branch (BHB) stars have standard intrinsic visible-light intensities {standard lights}. Type-1a-supernova intrinsic brightness varies directly with time visible, so brighter lasts longer (galaxies have one every hundred years). Quasars have standard intrinsic ultraviolet-light intensities. Comparing observed brightness to intrinsic brightness measures object distance, because brightness decreases with distance squared.
Galactic water-vapor clouds {water maser} have star formation.
Twelve constellations {Zodiac}| are in ecliptic. Sun is in Aquarius 1/21 to 2/20, Pisces 2/21 to 3/20, Aries 3/21 to 4/20, Taurus 4/21 to 5/20, Gemini 5/21 to 6/20, Cancer 6/21 to 7/20, Leo 7/21 to 8/20, Virgo 8/21 to 9/20, Libra 9/21 to 10/20, Scorpius 10/21 to 11/20, Sagittarius 11/21 to 12/20, and Capricorn 12/21 to 1/20.
Earth has a star {Sun}.
location
Sun is in galaxy horizontal plane, 27,000 light-years, 2/3 galaxy radius, from galaxy center, in Sagittarius arm.
orbit
Orbit around galaxy takes 2.5 x 10^6 years.
speed
Speed through space is 12 miles/second. Speed around galaxy is 150 miles/second.
formation
Sun and solar system formed 4,600,000,000 years ago, from gas cloud.
energy
Sun electromagnetic radiation is 10^33 ergs per second. Photons from Sun hit Earth with energy 1 eV, which is average needed for chemical reactions.
properties
Sun gas has atomic nuclei and electrons, with density 1.5 g/cm^3 at surface. Sun has average size. Mass is 2 x 10^30 kilograms, 10^6 times Earth mass. Diameter is 432,000 miles.
temperature
Temperature is 10^7 K at center and 5800 K at surface.
rotation
Equator rotates once every 27 days, around axis perpendicular to ecliptic. Polar regions rotate once every 23 to 24 days.
vibration
Sun vibrates with period 10 to 48 minutes after surface activity.
cycle
Sunspots, solar flares, and magnetic storms follow cycle of 11.1 years, with maximum at 1994 and 2005.
Light intensity from edge is 70% less than from center {limb-darkening}. Center is hotter. Edge is cooler. Edge light has to travel longer through Sun atmosphere.
Bright spots can be at Sun sides {parhelion}.
Inner sphere {inner core, Sun} has most of Sun mass and rotates once a day.
In next layer {radiative zone}, heat transfers only by radiation, not convection.
In layer {convective zone} under surface, turbulence and shock waves transfer heat by convection and make sunspots. Convective zone has 1% of Sun mass and 20% of radius.
Convective-zone gas-circulation pattern has 1,000,000-m swirls {granulation} and 30,000,000-m swirls {supergranulation}.
Strong magnetic fields near surface cause lower darker regions {sunspot}| of cooler 3900-K gas. Sunspots last 1 to 21 days and are 1 to 10 times wider than Earth. Sunspots start as small specks in horizontal belt, coagulate to make east-west pair, and then drift toward equator. Small sunspots {pore, Sun} can be near sunspots.
Above convective zone is layer {photosphere} that makes visible light, at 5700 K.
The layer {chromosphere} above photosphere makes star color, at 4500 K to 35,000 K. Photosphere and chromosphere are 9000 miles thick.
Chromosphere has luminous-material columns {spicule, Sun} 500,000 meters wide and 1,000,000 meters high, lasting 10 minutes.
Above chromosphere, low-density yellow layer {inner corona} extends from 9000 miles above surface to 300,000 miles above surface and is 10^5 to 10^6 K. Temperature is due mostly to solar flares. Alfven magnetic waves, whose field can oscillate but at constant pressure or which can change pressure like sound waves, affect temperature slightly. Corona temperature and density decrease over poles {coronal hole}.
High-speed electron and atomic-nucleus streams {solar prominence} {solar flare}| arch from chromosphere into inner corona, up to 400,000,000 meters high and 50,000,000 meters wide, for up to 30 minutes. Solar flares can make x-rays. Sunspots and solar flares can have large plasma ejections {coronal mass ejection} (CME).
cause
Magnetic lines with opposite polarity squeeze together along current sheet, where they break to form new ends that connect {magnetic field reconnection} {Sweet-Parker magnetic reconnection} {slow reconnection} {Petschek magnetic reconnection} {fast reconnection} with opposite-polarity lines and annihilate.
Corona high temperature is due mostly to solar flares. Magnetohydrodynamic waves {Alfven wave}, whose field can oscillate but at constant pressure or which can change pressure like sound waves, affect temperature slightly.
Above inner corona, a low-density white gas layer {outer corona} {K corona} ends 10^6 miles from surface.
Outer corona expands away from Sun in waves {solar wind}|, as 5 x 10^5 tons of charged particles per second leave at 500,000 meters per second.
Cool gas and dust {F corona} surround outer corona.
Sun has a magnetosphere {heliosphere}. Ionized-gas convection makes magnetic fields. Because Sun plasma conducts, magnetic fields flow around convective zone and core. Faster rotation at equator wraps magnetic force lines around Sun, making stronger magnetic field than with no wrapping: 1000 gauss rather than 1 gauss like Earth. Magnetic-force lines repulse each other, making gas less dense there.
Stars {blue dwarf} with mass less than 0.25 Sun mass can burn all hydrogen and then become white dwarfs.
Stars {brown dwarf} can have mass 13 to 80 times Jupiter mass or 7% Sun mass. Color is red, because it is ten times hotter than Jupiter. It burns deuterium but not hydrogen. It cannot burn lithium but has methane. Galaxy has 100,000,000,000 brown dwarfs. Objects {sub-brown dwarf} with mass less than 13 times Jupiter mass do not burn but only have heat from gravitational collapse.
In red-giant stars with mass more than 1.5 times, but less than 3 times, Sun mass, helium nuclear fusion to carbon at 10^8 K causes explosion. Stars {Cepheid variable star} {yellow supergiant} have a carbon center, helium layer, hydrogen-fusion layer, and hydrogen layer. Old stars in globular clusters and galactic nuclei are Cepheid variables {type-two Cepheid variable}.
65% of all stars are pairs {double star} or higher multiples. Large star typically has smaller stars circling it. Probably all stars have companion stars, black-dwarf companions, or planets. 15% of stars have black-dwarf companions. Perhaps, galaxies have 3000 x-ray-emitting double stars {x-ray star} with white-dwarf, pulsar, or black-hole companions.
Stars {dwarf star} can have less than 10% Sun mass.
Black holes {gravastar} can contain dark energy, which has negative gravity. Surface is ordinary matter.
Almost black holes {gray hole} can let light out, but then it falls back in.
Short-duration gamma-ray flares can come from stars {magnetar}, as star quakes disrupt magnetic field.
Dwarf stars {massive compact halo object} (MACHO) can be dark matter.
65% of all stars are pairs or higher multiples {multiple star}. Large stars typically have smaller stars circling. Probably all stars have companion stars, black-dwarf companions, or planets. 15% of stars have black-dwarf companions.
Stars {neutron star}| can be mostly neutrons, with density the same as atomic nuclei.
layers
Neutron stars have heavy-particle nucleus, neutron layer, elements up to atomic mass 140, and gas layer.
size
Neutron stars are 10,000-meter diameter and have mass the same as Sun mass.
temperature
Neutron stars have high temperature, because gravitational collapse turns potential energy into random kinetic energy.
spin
Neutron stars spin at 1 Hz to 30 Hz, because any initial rotation increases as diameter decreases.
magnetism
Few rotating neutron stars are magnetic, with magnetic field 10^12 times Earth field.
process
Neutron star starts with mass between 1.4 and 2.5 Sun mass. If mass is more, it becomes black hole rather than neutron star. If mass is less, it becomes white dwarf. After fusion forms iron at center, and nuclear reactions stop, heat and pressure decrease, and gravitational attraction causes a Type-Ib, Type-Ic, or Type-II supernova. Supernova explosions are typically asymmetric and push star through space at up to 1000 km/s. After supernova, gravitation is so great that it overcomes electron degeneracy pressure, and atoms collapse, leaving only neutrons, to keep total charge zero. Neutron stars balance gravity by neutron degeneracy pressure.
bursts
Once every 10 million years in galaxy, neutron stars collide and emit gamma-ray bursts {gamma-ray burst} (GRB). Neutron-star collisions make 95% of nuclei heavier than iron.
In red-giant stars with mass less than 1.25 Sun mass {Chandrasekhar limit, nova}, outer layers expand away by explosions {nova}|. For several months, nova radiates energy 10^6 times Sun energy. At any moment, galaxy has 1000 novas.
White dwarf remains. White dwarfs are 5% to 10% of all stars. White dwarfs fuse all hydrogen into helium, and then fuse all helium into carbon. Helium fusion is hotter than hydrogen fusion, so star is white. White dwarfs keep contracting and exploding. White dwarfs in binary star systems explode off outer layers every 30 to 50 years.
Young stars {population I star}, like Sun, have many metals, so they can have rocky planets.
Old stars {population II star} are in globular clusters, galactic halo, and galactic nucleus and have only hydrogen and helium, so they have no rocky planets.
Neutron stars {pulsar}| can emit radio waves with 1000 times greater intensity than Sun radiation. From them, Earth observers receive dozens of microwave pulses per second. Galaxy has million pulsars.
accretion-powered pulsar
Pulsars {accretion-powered pulsar} can accrete matter from companion stars and have matter-accretion disks that spin almost as fast as pulsar. Disk charge acceleration emits x-rays, not radio waves, because gravitational force is very high.
magnetar
Neutron-star magnetars can have magnetic field 10^10 tesla. Strong magnetic field accelerates charges, emitting x-rays constantly.
rotation-powered pulsar
Most pulsars {rotation-powered pulsar} emit microwave radiation by magnetic-field rotation. Such pulsars have magnetic fields 10^12 times Earth magnetic field and spin dozens of times per second. Pulsar radiation causes rotation-powered pulsars to spin slower as rotational energy is lost.
Rotation-powered pulsars can have companion stars and can accrete matter, typically increasing pulsar spin but weakening magnetic field. These pulsars spin tens or hundreds of times each second.
Rotation-powered pulsars {strong-field pulsar} can have stronger 10^8-tesla magnetic fields and spin once each second.
rotation-powered pulsar: poles
Magnetic poles typically do not align with spin axis. Magnetic field rotates at angle to pulsar rotation, causing electric fields. Electric fields accelerate charges from pulsar surface. Magnetic field aligns accelerated charges along magnetic poles. Accelerated charges have almost light speed and emit synchrotron-radiation microwaves. Synchrotron radiation lowers relativistic mass, to keep charges below light speed.
When charges have almost light speed, special relativity causes light waves not to radiate in all directions but form a beam in motion direction. Synchrotron radiation aligns along magnetic-pole axis. Microwave beams continuously radiate from both poles, in opposite directions. See Figure 1.
Because pulsars spin, magnetic-pole axis rotates. Axis can point toward Earth once each rotation. For most pulsars, magnetic-pole axis never points toward Earth. Because pulsars rotate, magnetic-pole axis can never constantly point at Earth.
Stars {pulsating star}, like RR Lyrae stars, can be average-size stars that can double brightness over hours or years, as they expand and contract up to 30%. Ion and helium layers change depth and cause brightness changes. Pulsating stars are less than 1% of stars.
After white dwarf is mostly carbon, it cools, first to yellow and then to red {red dwarf}. Eventually, it becomes dark.
Main-Sequence stars accumulate helium at center, as nuclear fusion turns hydrogen into helium. In stars with average mass, 30% of stars, when helium becomes more than hydrogen, helium fuses to make carbon. This makes star hotter, so hydrogen nuclear fusion becomes faster. Outer hydrogen layer expands. After 10^9 years, outer layer is thousands of times bigger and is cooler, so star {red giant}| is red.
Massive stars have extreme novas {supernova}|. For several months, star radiation is 10^9 times Sun radiation. Only 1% of stars become supernovas, so one galaxy has one supernova every 50 years. Sumerians saw a supernova (Mul Nun-ki) [-3000] in Vela. A supernova [185] lasted 20 months and was as bright as Moon. Supernova [393]. A supernova [1006] lasted years and was as bright as Moon. A type-2 supernova [1054] formed the Crab nebula. Supernova [1181]. Tycho observed a Type-1a supernova [1572], as bright as Venus. Kepler observed a supernova [1604].
Supernovas make all titanium through iron nuclei, mostly carbon, oxygen, silicon, magnesium, and iron. Supernovas also make five percent of elements heavier than iron.
Very young stars {T-Tauri star} have gas and dust around them.
Starting with hydrogen, stars first make helium, then carbon and oxygen, then heavier nuclei, such as silicon, sulfur, and calcium. Heat dissipates, and star stops fusion. Star still has high temperature and turbulence. Helium rises to surface, and heavier nuclei go to core. White-dwarf stars have no hydrogen and are small. White dwarfs orbiting stars with larger diameters but smaller masses can become supernovas {Type 1a supernova} {supernova 1a}. White dwarfs accrete gas from other star, until gas has enough matter to pressure star core to restart nuclear reactions. From carbon and oxygen, chain reactions produce nickel, iron, and cobalt and, after several seconds, explode star.
Stars with mass 8 to 25 times Sun mass start with hydrogen and first make helium, then carbon and oxygen, then heavier nuclei, such as silicon, magnesium, and iron. Such massive stars can fuse nuclei to make elements up to iron, which requires temperature 10^12 K. Such stars have turbulent hydrogen, helium, carbon, oxygen, silicon, magnesium, and iron layers, from surface to core, respectively. Star diameter is more than four million kilometers. Iron cannot fuse to anything else, so core becomes cooler and has less pressure. At critical pressure, gravitation collapses iron nuclei in one second to make neutron star. Gravitation continues to pull matter inward, and nuclei bounce off neutron star turbulently at supersonic speed, making shock waves. Nuclei stream inward between shock-wave sides. Neutrinos heat shock-wave gas, which keeps expanding. Shock waves explode star {Type 1b supernova} {Type 1c supernova} {Type 2 supernova} {supernova 2}. Asymmetrical explosion pushes neutron star to speeds up to 1000 km/s. Explosion makes high temperature and pressure and can make elements higher than iron. Perhaps, higher-element making involves antineutrinos. Higher-element making uses energy rather than making energy, absorbs heat, and cools core. Expansion weakens, and gravitational collapse takes several minutes.
In red-giant stars with mass less than 1.25 Sun mass {Chandrasekhar limit, white dwarf}, as outer layers expand away by nova explosions, Earth-size star {white dwarf} remains. Electron-degeneracy pressure counterbalances gravity, so atoms do not collapse. White dwarfs are 5% to 10% of all stars.
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Date Modified: 2022.0225