"begins to radiate at about 10 K, upon formation, while its greater interior mass is at 10 K but cannot radiate through its normal matter shell. The visible radiation emitted by white dwarfs varies over a wide color range, from the blue-white color of an O-type main sequence star to the red of an M-type red dwarf. White dwarf effective surface temperatures extend from over 150,000 K to barely under 4,000 K. In accordance with the Stefan–Boltzmann law, luminosity increases with increasing surface temperature; this surface temperature range corresponds to a luminosity from over 100 times the Sun's to under"
"time, the red giant had a radius of . It is thought that the red giant phase of the current white dwarf was shortened from around 100 million years on average, to a few decades—while the brown dwarf was within the red giant, it hastened the expulsion of matter during this phase by rapidly heating gas and accreting a portion of it. During this phase, drag from the red giant also decreased the orbital speed of the brown dwarf, causing it to fall inwards. The orbit of the brown dwarf is slowly decaying. In about 1.4 billion years, it is"
"released by this size reduction is converted into heat, which is carried throughout the star by convection. According to computer simulations, the minimum mass a red dwarf must have in order to eventually evolve into a red giant is ; less massive objects, as they age, would increase their surface temperatures and luminosities becoming blue dwarfs and finally white dwarfs. The less massive the star, the longer this evolutionary process takes. It has been calculated that a red dwarf (approximately the mass of the nearby Barnard's Star) would stay on the main sequence for 2.5 trillion years, followed by five"
"A white dwarf is the remnant of a small to medium size star (our sun is an example of these). At the end of its life, the star has burned its hydrogen and helium fuel, and thermonuclear fusion processes cease. The star does not have enough mass to either burn much heavier elements, or to implode into a neutron star or type II supernova as a larger star can, from the force of its own gravity, so it gradually shrinks and becomes very dense as it cools, glowing white and then red, for a period many times longer than the"
"faster than those. A white dwarf is stable once formed and will continue to cool almost indefinitely, eventually to become a black dwarf. Assuming that the Universe continues to expand, it is thought that in 10 to 10 years, the galaxies will evaporate as their stars escape into intergalactic space. White dwarfs should generally survive galactic dispersion, although an occasional collision between white dwarfs may produce a new fusing star or a super-Chandrasekhar mass white dwarf which will explode in a Type Ia supernova. The subsequent lifetime of white dwarfs is thought to be on the order of the lifetime"
"and falls on its surface in the end. At least during the active phase an accretion disk forms around the white dwarf. During the ""quiescent"" phase, most of the white dwarf luminosity comes from stable hydrogen burning on its surface, and photons emitted this way ionize the wind of the red giant which causes nebular emission. The giant star, however, follows a quasi-periodic activity cycle (similar to the solar cycle) roughly every 7,550 days; when the activity of the star is enhanced, the stellar wind becomes stronger, and in response the white dwarf increases in size and cools, triggering the"
"times its previous size and becomes a red giant, such as Aldebaran (or Alpha Tauri). Eventually the red giant sheds its outer layers of gas, which become a planetary nebula, while the core rapidly cools and contracts into a compact, dense white dwarf. The revised Yerkes Atlas system (Johnson & Morgan 1953) listed 11 G-type dwarf spectral standard stars; however, not all of these have survived to this day as standards. The ""anchor points"" of the MK spectral classification system among the G-type main-sequence dwarf stars, i.e. those standard stars that have remained unchanged over years, are beta CVn (G0V),"
"equilibrium. Stars larger than red dwarfs do this by increasing their size and becoming red giants with larger surface areas. Rather than expanding, however, red dwarfs with less than 0.25 solar masses are predicted to increase their radiative rate by increasing their surface temperatures and becoming ""bluer"". This is because the surface layers of red dwarfs do not become significantly more opaque with increasing temperature. Blue dwarfs eventually evolve into white dwarfs once their hydrogen fuel is completely exhausted, which in turn will eventually cool to become black dwarfs. Blue dwarf (red-dwarf stage) A blue dwarf is a predicted class"
"outer layers of intermediate-mass stars cool sufficiently to become opaque, their hydrogen shells increase in temperature and the stars start to become more luminous. This is known as the red giant branch; it is a relatively long-lived stage and it appears prominently in H-R diagrams. These stars will eventually end their lives as white dwarfs. The most massive stars do not become red giants, instead their cores quickly become hot enough to fuse helium and eventually heavier elements and they are known as supergiants. They follow approximately horizontal evolutionary tracks from the main sequence across the top of the H-R"
"will steadily cool as the remaining heat is radiated into space over more than two billion years. A white dwarf forms only after the star has evolved from the main sequence and then passed through a red giant stage. This occurred when Sirius B was less than half its current age, around 120 million years ago. The original star had an estimated and was a B-type star (roughly B4–5) when it was still on the main sequence. While it passed through the red giant stage, Sirius B may have enriched the metallicity of its companion. This star is primarily composed"
"will then become a white dwarf star, radiating 10 Watts that sustains 1e13 kg biomass for an immense hundred million trillion (10) years, contributing a time-integrated ""BIOTA"" of 10 years. The 10 white dwarfs that may exist in the galaxy during this time can then contribute a time-integrated ""BIOTA"" of 10 kg-years. Red dwarf stars with luminosities of 10 Watts and life-times of 10 years can contribute 10 kg-years each, and 10 red dwarfs can contribute 10 kg-years, while brown dwarfs can contribute 10 kg-years of time-integrated biomass (""BIOTA"") in the galaxy. In total, the energy output of stars during"
"be a red dwarf that is nondetectable at that range). Spectroscopic analysis and calculation gave an estimate of 125 parsecs (407.5 light years). The system consists of a white dwarf and a donor star which orbit around a common centre of gravity every 1.5 hours. The white dwarf sucks matter from the other star onto an accretion disc and periodically erupts, reaching apparent magnitude 11.2 in superoutbursts, 12.1 in normal outbursts and remaining at magnitude 16.7 when quiet. The ""superhumps"" see the star increase by 0.24 magnitude for 1.55 hours during these superoutbursts. Spectroscopic observations of the white dwarf with"
"a lifetime of a few hundred million years. Finally brown dwarfs can form new stars colliding with each other to form a red dwarf star, that can survive for 10 (10 trillion) years, or accreting gas at very slow rates from the remaining interstellar medium until they have enough mass to start hydrogen burning as red dwarfs too. This process, at least on white dwarfs, could induce Type Ia supernovae too. Over time, the orbits of planets will decay due to gravitational radiation, or planets will be ejected from their local systems by gravitational perturbations caused by encounters with another"
"white dwarfs, they are extremely dense, being composed of degenerate matter, and so have radii of order the radius of Earth. Astronomers believe that the two stars will eventually merge, based on data from many X-ray satellites, such as Chandra X-Ray Observatory, XMM-Newton and the Swift Gamma-Ray Burst Mission. These data show that the orbital period of the two stars is steadily decreasing at a rate of 1.2 milliseconds per year as they thus are getting closer by approximately per day. At this rate, they can be expected to merge in approximately 340,000 years. With a revolution period of 5.4"
"becomes a white dwarf. The white dwarf is surrounded by an expanding shell of gas in an object known as a planetary nebula. Planetary nebulae seem to mark the transition of a medium mass star from red giant to white dwarf. X-ray images reveal clouds of multimillion degree gas that have been compressed and heated by the fast stellar wind. Eventually the central star collapses to form a white dwarf. For a billion or so years after a star collapses to form a white dwarf, it is ""white"" hot with surface temperatures of ~20,000 K. X-ray emission has been detected"
"produce oxygen. It is worth noting that the violent flaring period of a red dwarf's life cycle is estimated to only last roughly the first 1.2 billion years of its existence. If a planet forms far away from a red dwarf so as to avoid tidelock, and then migrates into the star's habitable zone after this turbulent initial period, it is possible for life to have a chance to develop. The major advantage that red dwarfs have over other stars as abodes for life: they produce light energy for a very long time. It took 4.5 billion years before humans"
"times brighter than the Sun), with little variation. The model for the formation of this category of supernova is a closed binary star system. The larger of the two stars is the first to evolve off the main sequence, and it expands to form a red giant. The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue nuclear fusion. At this point it becomes a white dwarf star, composed primarily of carbon and oxygen. Eventually the secondary star also"
"mass, reducing the angular momentum, orbital radius and period. After the primary has degenerated into a white dwarf, the secondary star later evolves into a red giant and the stage is set for mass accretion onto the primary. During this final shared-envelope phase, the two stars spiral in closer together as angular momentum is lost. The resulting orbit can have a period as brief as a few hours. If the accretion continues long enough, the white dwarf may eventually approach the Chandrasekhar limit. The white dwarf companion could also accrete matter from other types of companions, including a subgiant or"
"stellar evolution). Thus, the longest living stars in the universe are low-mass red dwarfs, with a mass of about 0.08 solar masses (), which have a lifetime of order 10 (10 trillion) years. Coincidentally, this is comparable to the length of time over which star formation takes place. Once star formation ends and the least massive red dwarfs exhaust their fuel, nuclear fusion will cease. The low-mass red dwarfs will cool and become black dwarfs. The only objects remaining with more than planetary mass will be brown dwarfs, with mass less than , and degenerate remnants; white dwarfs, produced by"
"system consists of a red dwarf of spectral type M6 and a white dwarf that orbit each other every seven hours; the former is 18% as massive as the Sun, while the latter has 44% of the Sun's mass. The red dwarf is tidally locked with the white dwarf, meaning it displays the same side to the heavier star. The system is also a post-common-envelope binary, and the red dwarf star is transferring material onto the white dwarf. In approximately 9–20 billion years, RR Caeli will likely become a cataclysmic variable star due to the period's gradual shortening, leading to"
"region. They may be called ""pre-white dwarfs"". These variables all exhibit small (1%–30%) variations in light output, arising from a superposition of vibrational modes with periods of hundreds to thousands of seconds. Observation of these variations gives asteroseismological evidence about the interiors of white dwarfs. White dwarfs are thought to represent the end point of stellar evolution for main-sequence stars with masses from about 0.07 to 10 . The composition of the white dwarf produced will depend on the initial mass of the star. Current galactic models suggest the Milky Way galaxy currently contains about ten billion white dwarfs. If"
"these evolve to Wolf Rayet stars before exploding. Red supergiants are necessarily no more than about 25 million years old and such massive stars are expected to form only in relatively large clusters of stars, so they are expected to be found mostly near prominent clusters. However they are fairly short-lived compared to other phases in the life of a star and only form from relatively uncommon massive stars, so there will generally only be small numbers of red supergiants in each cluster at any one time. For example, in the substantial Double Clusters in Perseus there is just a"
"a binary consisting of a white dwarf and a low-mass giant evolve through a common-envelope (CE) phase. The outcome of the CE will be a double white-dwarf binary. Through the emission of gravitational radiation, the binary loses angular momentum, which causes the binary orbit to shrink. When the orbital period has shrunk to about 5 minutes, the less-massive (and the larger) of the two white dwarfs will fill its Roche lobe and start mass transfer to its companion. Soon after the onset of mass transfer, the orbital evolution will reverse and the binary orbit will expand. It is in this"
"value. The most rapid part of the Sun's expansion into a red giant will occur during the final stages, when the Sun will be about 12 billion years old. It is likely to expand to swallow both Mercury and Venus, reaching a maximum radius of . The Earth will interact tidally with the Sun's outer atmosphere, which would serve to decrease Earth's orbital radius. Drag from the chromosphere of the Sun would also reduce the Earth's orbit. These effects will act to counterbalance the effect of mass loss by the Sun, and the Earth will probably be engulfed by the"
"dwarfs. However, studies of the Hyades show that it is deficient in stars at both extremes of mass. At an age of 625 million years, the cluster's main sequence turn-off is about , meaning that all heavier stars have evolved into subgiants, giants, or white dwarfs, while less massive stars continue fusing hydrogen on the main sequence. Extensive surveys have revealed a total of 8 white dwarfs in the cluster core, corresponding to the final evolutionary stage of its original population of B-type stars (each about ). The preceding evolutionary stage is currently represented by the cluster's four red clump"
"be habitable for another , possibly up to if nitrogen is removed from the atmosphere. Even if the Sun were eternal and stable, 27% of the water in the modern oceans will descend to the mantle in one billion years, due to reduced steam venting from mid-ocean ridges. The Sun will evolve to become a red giant in about . Models predict that the Sun will expand to roughly , about 250 times its present radius. Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will"
"the white dwarf to produce a thermonuclear explosion. The white dwarf orbits close to the red giant, with an accretion disc concentrating the overflowing atmosphere of the red giant onto the white dwarf. RS Ophiuchi is a system consisting of a white dwarf with a red giant companion. The stars are in a binary system with an orbital period of around 454 days. The 1898 eruption was, in fact, not discovered until several years after it happened. Williamina Fleming discovered a nova-like spectrum in the Henry Draper Memorial photographs and announced it as a potential nova in 1904. This diagnosis"
"cores becomes depleted. Then they expand and cool to become supergiants. They spend a few thousand years as a yellow supergiant while cooling, then spend one to four million years as a red supergiant, typically. Supergiants make up less than 1% of stars; though different proportions in the visible early eras of the universe. The relatively brief phases and concentration of matter explains the rarity of these stars. Some red supergiants undergo a ""blue loop"", temporarily re-heating and becoming yellow or even blue supergiants before cooling again. Stellar models show that blue loops rely on particular chemical makeups and other"
"and the creation of a planetary nebula finally ends the red-giant phase of the star's evolution. The red-giant phase typically lasts only around a billion years in total for a solar mass star, almost all of which is spent on the red-giant branch. The horizontal-branch and asymptotic-giant-branch phases proceed tens of times faster. If the star has about 0.2 to , it is massive enough to become a red giant but does not have enough mass to initiate the fusion of helium. These ""intermediate"" stars cool somewhat and increase their luminosity but never achieve the tip of the red-giant branch"
"increases as the mass decreases, the luminosity increases, and more fusion products are dredged up to the surface. They ""ascend"" the AGB until the mass loss becomes so extreme that they start to increase in temperature and enter the post-AGB phase, eventually to become a white dwarf. The evolution of a Mira variable should cause its period to increase, assuming it stays with the unstable region of pulsations. However, this secular trend is interrupted by the thermal pulses. These thermal pulses occur tens of thousands of years apart, but are theorised to produce rapid period changes over less than a"
"gradually becomes denser. It is estimated that the Sun has become 30% brighter in the last 4.5 billion years. At present, it is increasing in brightness by about 1% every 100 million years. The Sun does not have enough mass to explode as a supernova. Instead it will exit the main sequence in approximately 5 billion years and start to turn into a red giant. As a red giant, the Sun will grow so large that it will engulf Mercury, Venus, and probably Earth. Even before it becomes a red giant, the luminosity of the Sun will have nearly doubled,"
"entered its red giant phase. GD 362 has been a white dwarf for approximately 900 million years. GD 362 GD 362 is a white dwarf approximately 150 light years from Earth. In 2004, spectroscopic observations showed that it had a relatively high concentration of metals in its atmosphere. Since the high gravitational field of white dwarfs quickly forces heavy elements to settle towards the bottom of the atmosphere, this meant that the atmosphere was being polluted by an external source. In 2005, infrared photometric observations suggested that it was surrounded by a ring of dust with size comparable to the"
"a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist. Over the following approximately 4 billion years, the energy output of the Sun increased and atmospheric composition changed. The Great Oxygenation Event—oxygenation of the atmosphere around 2.4 billion years ago—was the most notable alteration. Over the next five billion years from the present, the Sun's ultimate death as it becomes a red giant and then a white dwarf will have large effects on climate, with the red giant phase possibly ending any life on Earth that survives until that time. Solar output varies on shorter time"