which region of the h-r diagram does the high mass star moves to when it leaves the main sequence
Main sequence


They follow approximately horizontal evolutionary tracks from the main sequence across the top of the H-R diagram. Supergiants are relatively rare and do not show prominently on most H-R diagrams. Their cores will eventually collapse, usually leading to a supernova and leaving behind either a neutron star or black hole. When a cluster of stars is formed at about the same time, the main sequence lifespan of these stars will depend on their individual masses. The most massive stars will leave the main sequence first, followed in sequence by
19833948
Subgiant


red giants is entirely empty, with no subgiants. Stellar evolutionary tracks can be plotted on an H–R diagram. For a particular mass, these trace the position of a star throughout its life, and show a track from the initial main sequence position, along the subgiant branch, to the giant branch. When an H–R diagram is plotted for a group of stars which all have the same age, such as a cluster, the subgiant branch may be visible as a band of stars between the main sequence
18305100
Cosmic distance ladder


, used on progressively larger distance scales, include: When the absolute magnitude for a group of stars is plotted against the spectral classification of the star, in a Hertzsprung–Russell diagram, evolutionary patterns are found that relate to the mass, age and composition of the star. In particular, during their hydrogen burning period, stars lie along a curve in the diagram called the main sequence. By measuring these properties from a star's spectrum, the position of a main sequence star on the H–R diagram can be
12430367
Blue loop


rapidly losing mass. The most luminous red supergiants can lose mass quickly enough that they become hotter and smaller. In the most massive stars, this can result in the star evolving permanently away from the red supergiant stage to become a blue supergiant, but in some cases the star will execute a blue loop and return to being a red supergiant. Stars which are executing blue loops cross the yellow portion of the H-R diagram above the main sequence, so that many of them cross a region called the instability strip because
21669313
Star formation


's main sequence phase on the H–R diagram. The stages of the process are well defined in stars with masses around or less. In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined. The later evolution of stars are studied in stellar evolution. Key elements of star formation are only available by observing in wavelengths other than the optical. The protostellar stage of stellar existence is almost invariably hidden away
73798
Subgiant


Subgiants occupy a region above (i.e. more luminous than) the main sequence stars and below the giant stars. There are relatively few on most H–R diagrams because the time spent as a subgiant is much less than the time spent on the main sequence or as a giant star. Hot, class B, subgiants are barely distinguishable from the main sequence stars, while cooler subgiants fill a relatively large gap between cool main sequence stars and the red giants. Below approximately spectral type K3 the region between the main sequence and
18305099
Blue straggler


time, and thus in an H–R diagram for a cluster, all stars should lie along a clearly defined curve set by the age of the cluster, with the positions of individual stars on that curve determined solely by their initial mass. With masses two to three times that of the rest of the main-sequence cluster stars, blue stragglers seem to be exceptions to this rule. The resolution of this problem is likely related to interactions between two or more stars in the dense confines of the clusters in which blue
227735
Main sequence


the star forming a convective envelope steadily increases. Main-sequence stars below undergo convection throughout their mass. When core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen. In general, the more massive a star is, the shorter its lifespan on the main sequence. After the hydrogen fuel at the core has been consumed, the star evolves away from the main sequence on the HR diagram, into a supergiant, red giant, or directly to a white dwarf. In the
19833904
Betelgeuse


a high-mass multiple system within Ori OB1a, Betelgeuse was probably formed about 10–12 million years ago, but has evolved rapidly due to its high mass. In 2015, H. Bouy and J. Alves suggested that Betelgeuse may instead be a member of the newly-discovered Taurion OB association. Like many young stars in Orion whose mass is greater than , Betelgeuse will use its fuel quickly and not live long. On the Hertzsprung–Russell diagram, Betelgeuse has moved off the main sequence and has swelled and cooled to become a
9241999
Subgiant


instead of reaching the red giant branch are lower at low metallicity. A Hertzsprung–Russell (H–R) diagram is a scatter plot of stars with temperature or spectral type on the x-axis and absolute magnitude or luminosity on the y-axis. H–R diagrams of all stars, show a clear diagonal main sequence band containing the majority of stars, a significant number of red giants (and white dwarfs if sufficiently faint stars are observed), with relatively few stars in other parts of the diagram.
18305098
Color–color diagram


of main sequence stars are well known, a theoretical main sequence can be plotted for reference, as is done with the solid black line in the example to the right. Interstellar dust scattering is also well understood, allowing bands to be drawn on a color–color diagram defining the region in which stars reddened by interstellar dust are expected to be observed, indicated on the color–color diagram by dashed lines. The typical axes for infrared color–color diagrams have (H–K) on the horizontal axis and (
5762729
Main sequence


their cores and so they mark the lower edge of main sequence fuzziness caused by variance in chemical composition. A nearly vertical region of the HR diagram, known as the instability strip, is occupied by pulsating variable stars known as Cepheid variables. These stars vary in magnitude at regular intervals, giving them a pulsating appearance. The strip intersects the upper part of the main sequence in the region of class "A" and "F" stars, which are between one and two solar masses. Pulsating stars in this part of
19833936
Hypergiant


rotating stars with enhanced convection and mixing, may skip these steps and move directly to the Wolf–Rayet stage. This means that stars at the top of the Hertzsprung–Russell diagram where hypergiants are found may be newly evolved from the main sequence and still with high mass, or much more evolved post-red supergiant stars that have lost a significant fraction of their initial mass, and these objects cannot be distinguished simply on the basis of their luminosity and temperature. High-mass stars with a high proportion of remaining
6522160
Main sequence


, or the 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.
19833947
Subgiant


when they leave the main sequence. The exact initial mass at which stars will show a hook and at which they will leave the main sequence with cores above the Schönberg–Chandrasekhar limit depend on the metallicity and the degree of overshooting in the convective core. Low metallicity causes the central part of even low mass cores to be convectively unstable, and overshooting causes the core to be larger when hydrogen becomes exhausted. Once the core exceeds the C-R limit, it can no longer remain in thermal equilibrium with the hydrogen shell
18305090
Color–color diagram


J–H) on the vertical axis (see infrared astronomy for information on band color designations). On a diagram with these axes, stars which fall to the right of the main sequence and the reddening bands drawn are significantly brighter in the K band than main sequence stars, including main sequence stars which have experienced reddening due to interstellar dust. Of the J, H, and K bands, K is the longest wavelength, so objects which are anomalously bright in the K band are said to exhibit infrared excess.
5762730
Messier 67


F, other than perhaps some of the blue stragglers, since the brighter stars of that age have already left the main sequence. In fact, when the stars of the cluster are plotted on the Hertzsprung-Russell diagram, there is a distinct "turn-off" representing the stars which have terminated hydrogen fusion in the core and are destined to become red giants. As the cluster ages, the turn-off moves progressively down the main sequence. It appears that M67 does not contain an unbiased sample of stars.
7867147
Subgiant


branch as for lower mass stars. The core contraction and envelop expansion is very rapid, taking only a few million years. In this time the temperature of the star will cool from its main sequence value of 6,000–30,000 K to around 5,000 K. Relatively few stars are seen in this stage of their evolution and there is an apparent lack in the H–R diagram known as the Hertzsprung gap. It is most obvious in clusters from a few hundred million to a few billion years old. Beyond about , depending on metallicity,
18305092
Turnoff point


The turnoff point for a star refers to the point on the Hertzsprung-Russell diagram where it leaves the main sequence after the exhaustion of its main fuel. It is often referred to as the main sequence turnoff. By plotting the turnoff point of the stars in star clusters, one can estimate the cluster's age. Red dwarfs are stars of 0.08-0.4 solar masses and are also referred to as class M stars. Red dwarfs have sufficient hydrogen mass to sustain hydrogen fusion to helium via the proton-proton chain reaction
299636
Main sequence


an approximation, however, and the mass-luminosity relation can vary depending on a star's composition. When a main-sequence star has consumed the hydrogen at its core, the loss of energy generation causes its gravitational collapse to resume and the star evolves off the main sequence. The path which the star follows across the HR diagram is called an evolutionary track. Stars with less than , are predicted to directly become white dwarfs when energy generation by nuclear fusion of hydrogen at their core comes to a halt although no stars
19833945
Messier 79


stars in this cluster are red giants. The elongated branch is the red giant branch. Some of the stars in the diagram, including those extending outward from the red giant branch toward the upper left, are actually foreground stars that are not members of the cluster. Altogether three regions of the Hertzsprung-Russell diagram are present here: the low-mass end of the main sequence, the complete red giant branch and the horizontal branch. Compared to optical bands, in infrared bands the lower main sequence is shallower and the
8331625
Pre-main-sequence star


A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas. After the protostar blows away this envelope, it is optically visible, and appears on the stellar birthline in the Hertzsprung-Russell diagram. At this point, the star has acquired nearly all of its mass but has
18679331
Hertzsprung–Russell diagram


structure and the evolution of stars produce plots that match those from observations. This type of diagram could be called "temperature-luminosity diagram", but this term is hardly ever used; when the distinction is made, this form is called the "theoretical Hertzsprung–Russell diagram" instead. A peculiar characteristic of this form of the H–R diagram is that the temperatures are plotted from high temperature to low temperature, which aids in comparing this form of the H–R diagram with the observational form. Although the
10477971
Giant star


already very luminous and they move horizontally across the HR diagram when they leave the main sequence, briefly becoming blue giants before they expand further into blue supergiants. They start core-helium burning before the core becomes degenerate and develop smoothly into red supergiants without a strong increase in luminosity. At this stage they have comparable luminosities to bright AGB stars although they have much higher masses, but will further increase in luminosity as they burn heavier elements and eventually become a supernova. Stars in the range have somewhat intermediate properties and have been
11942421
Hertzsprung gap


The Hertzsprung Gap is a feature of the Hertzsprung–Russell diagram for a star cluster. It is named after Ejnar Hertzsprung, who first noticed the absence of stars in the region of the Hertzsprung–Russell diagram between A5 and G0 spectral type and between +1 and −3 absolute magnitudes (i.e. between the top of the main sequence and the red giants for stars above roughly 1.5 solar mass. When a star during its evolution crosses the Hertzsprung gap, it means that it has finished core hydrogen burning, but has yet to start
19352208
Henyey track


The Henyey track is a path taken by pre-main-sequence stars with masses 0.5 Solar mass in the Hertzsprung–Russell diagram after the end of Hayashi track. The astronomer Louis G. Henyey and his colleagues in the 1950s, showed that the pre-main-sequence star can remain in radiative equilibrium throughout some period of its contraction to the main sequence. The Henyey track is characterized by a slow collapse in near hydrostatic equilibrium. They are approaching the main sequence almost horizontally in the Hertzsprung–Russell diagram (i.e. the
709156
Hertzsprung–Russell diagram


+1 and −3 absolute magnitudes ("i.e." between the top of the main sequence and the giants in the horizontal branch). RR Lyrae variable stars can be found in the left of this gap on a section of the diagram called the instability strip. Cepheid variables also fall on the instability strip, at higher luminosities. The H-R diagram can be used by scientists to roughly measure how far away a star cluster or galaxy is from Earth. This can be done by comparing the apparent magnitudes of the stars in
10477975
Main sequence


This effect results in a broadening of the main sequence band because stars are observed at random stages in their lifetime. That is, the main sequence band develops a thickness on the HR diagram; it is not simply a narrow line. Other factors that broaden the main sequence band on the HR diagram include uncertainty in the distance to stars and the presence of unresolved binary stars that can alter the observed stellar parameters. However, even perfect observation would show a fuzzy main sequence because mass is not the only parameter that affects a
19833934
Blue giant


In astronomy, a blue giant is a hot star with a luminosity class of III (giant) or II (bright giant). In the standard Hertzsprung–Russell diagram, these stars lie above and to the right of the main sequence. The term applies to a variety of stars in different phases of development, all evolved stars that have moved from the main sequence but have little else in common, so blue giant simply refers to stars in a particular region of the HR diagram rather than a specific type of star
4165697
Red giant


, and so the outer layers of the star expand greatly, absorbing most of the extra energy from shell fusion. This process of cooling and expanding is the subgiant branch. When the envelope of the star cools sufficiently it becomes convective, the star stops expanding, its luminosity starts to increase, and the star is ascending the red giant branch of the Hertzsprung–Russell (H–R) diagram. The evolutionary path the star takes as it moves along the red-giant branch depends on the mass of the star.
6522556
Globular cluster


a red star with a cool surface temperature, while negative values imply a blue star with a hotter surface. When the stars near the Sun are plotted on an HR diagram, it displays a distribution of stars of various masses, ages, and compositions. Many of the stars lie relatively close to a sloping curve with increasing absolute magnitude as the stars are hotter, known as main-sequence stars. However the diagram also typically includes stars that are in later stages of their evolution and have wandered away from this main-
12584271
Stellar evolution


matter and preventing further gravitational collapse. The star thus evolves rapidly to a stable state, beginning the main-sequence phase of its evolution. A new star will sit at a specific point on the main sequence of the Hertzsprung–Russell diagram, with the main-sequence spectral type depending upon the mass of the star. Small, relatively cold, low-mass red dwarfs fuse hydrogen slowly and will remain on the main sequence for hundreds of billions of years or longer, whereas massive, hot O-type stars will
8344783
Main sequence


position on the main sequence until a significant amount of hydrogen in the core has been consumed, then begins to evolve into a more luminous star. (On the HR diagram, the evolving star moves up and to the right of the main sequence.) Thus the main sequence represents the primary hydrogen-burning stage of a star's lifetime. The majority of stars on a typical HR diagram lie along the main-sequence curve. This line is pronounced because both the spectral type and the luminosity depend only on a star
19833915
IK Pegasi


horizontal branch star. That is, it belonged to a group of stars that fall upon a roughly horizontal line on the H-R diagram. The fusion of helium formed an inert core of carbon and oxygen. When helium was exhausted in the core a helium-burning shell formed in addition to the hydrogen-burning one and the star moved to what astronomers term the asymptotic giant branch, or AGB. (This is a track leading to the upper-right corner of the H-R diagram.) If the
6313459
Hertzsprung–Russell diagram


uncertainties incurred in the conversions between theoretical quantities and observations. Most of the stars occupy the region in the diagram along the line called the main sequence. During the stage of their lives in which stars are found on the main sequence line, they are fusing hydrogen in their cores. The next concentration of stars is on the horizontal branch (helium fusion in the core and hydrogen burning in a shell surrounding the core). Another prominent feature is the Hertzsprung gap located in the region between A5 and G0 spectral type and between
10477974
Blue supergiant star


Blue supergiant stars are hot luminous stars, referred to scientifically as OB supergiants. They have luminosity class I and spectral class B9 or earlier. Blue supergiants (BSGs) are found towards the top left of the Hertzsprung–Russell diagram to the right of the main sequence. They are larger than the Sun but smaller than a red supergiant, with surface temperatures of 10,000–50,000 K and luminosities from about 10,000 to a million times the Sun. Supergiants are evolved high-mass stars, larger and more luminous than main-sequence stars
4165709
Stellar nucleosynthesis


about . As a main sequence star ages, the core temperature will rise, resulting in a steadily increasing contribution from its CNO cycle. Main sequence stars accumulate helium in their cores as a result of hydrogen fusion, but the core does not become hot enough to initiate helium fusion. Helium fusion first begins when a star leaves the red giant branch after accumulating sufficient helium in its core to ignite it. In stars around the mass of the sun, this begins at the tip of the red giant branch with a helium flash
19187437
Color–color diagram


. The dust itself then begins to radiate as a blackbody, though one much cooler than the star. As a result, an excess of infrared radiation is observed for the star. Even without circumstellar dust, regions undergoing star formation exhibit high infrared luminosities compared to stars on the main sequence. Each of these effects is distinct from the reddening of starlight which occurs as a result of scattering off of dust in the interstellar medium. Color–color diagrams allow for these effects to be isolated. As the color–color relationships
5762728
Convection zone


envelope of the star contains a region where partial ionization of hydrogen and helium raises the heat capacity. The relatively low temperature in this region simultaneously causes the opacity due to heavier elements to be high enough to produce a steep temperature gradient. This combination of circumstances produces an outer convection zone, the top of which is visible in the Sun as solar granulation. Low mass main sequences of stars, such as red dwarfs below 0.35 solar masses, as well as pre-main sequence stars on the Hayashi track, are convective throughout
2880789
Sher 25


Sher 25 is a blue supergiant star in the constellation Carina, located approximately 25,000 light years from the Sun in the H II region NGC 3603 of the Milky Way. It is a spectral type B1Iab star with an apparent magnitude of 12.2. Its initial main sequence mass is calculated at 60 times the mass of our Sun, but a star of this type will have already lost a substantial fraction of that mass. It is unclear whether Sher 25 has been through a red supergiant phase or has just evolved from the main sequence
3258422
Hayashi track


and Ezer & Cameron realistically simulated pre-main-sequence evolution, including the Henyey track that stars follow after leaving the Hayashi track. These standard PMS tracks can still be found in textbooks on stellar evolution. The forbidden zone is the region on the HR diagram to the right of the Hayashi track where no star can be in hydrostatic equilibrium, even those that are partially or fully radiative. Newborn protostars start out in this zone, but are not in hydrostatic equilibrium and will rapidly move towards the Hayashi track. Because stars
22151862
Main sequence


an insulating effect that retains more energy at the core, so the star does not need to produce as much energy to remain in hydrostatic equilibrium. By contrast, a lower opacity means energy escapes more rapidly and the star must burn more fuel to remain in equilibrium. Note, however, that a sufficiently high opacity can result in energy transport via convection, which changes the conditions needed to remain in equilibrium. In high-mass main-sequence stars, the opacity is dominated by electron scattering, which is nearly constant with
19833943
Van Maanen 2


large proper motions in which he identified what he called "van Maanen's star" as one of only three known white dwarfs, a term he coined. These are stars that have an unusually low absolute magnitude for their spectral class, lying well below the main sequence on the Hertzsprung–Russell diagram of stellar temperature vs. luminosity. The high mass density of white dwarfs was demonstrated in 1925 by American astronomer Walter Adams when he measured the gravitational redshift of Sirius B as 21 km/s. In 1926, British astrophysicist Ralph
10448902
Red dwarf


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 billion years as a blue dwarf, during which the star would have one third of the Sun's luminosity () and a surface temperature of 6,500–8,500 kelvins. The fact that red dwarfs and other low-mass stars still remain on the main sequence when more massive stars have moved off the main sequence allows
11476484
Main sequence


the star as an idealized energy radiator known as a black body, the luminosity "L" and radius "R" can be related to the effective temperature "T" by the Stefan–Boltzmann law: where "σ" is the Stefan–Boltzmann constant. As the position of a star on the HR diagram shows its approximate luminosity, this relation can be used to estimate its radius. The mass, radius and luminosity of a star are closely interlinked, and their respective values can be approximated by three relations.
19833920
Supergiant star


is a clue to their nature as stars even more evolved than supergiants. Just as the AGB stars occur in almost the same region of the HR diagram as red supergiants, Wolf–Rayet stars can occur in the same region of the HR diagram as the hottest blue supergiants and main-sequence stars. The most massive and luminous main-sequence stars are almost indistinguishable from the supergiants they quickly evolve into. They have almost identical temperatures and very similar luminosities, and only the most detailed analyses can distinguish the spectral features that
7159996
Beta Pictoris


main sequence stars of spectral type A fall into a region of the Hertzsprung–Russell diagram called the instability strip, which is occupied by pulsating variable stars. In 2003, photometric monitoring of the star revealed variations in brightness of around 1–2 millimagnitudes on frequencies between about 30 and 40 minutes. Radial velocity studies of Beta Pictoris also reveal variability: there are pulsations at two frequencies, one at 30.4 minutes and one at 36.9 minutes. As a result, the star is classified as a Delta Scuti variable. The mass of Beta
6990750
HD 154088


of Nearby Stars indicated a distance of about 50 light-years. The star has a spectral type of K0V, indicating that it is a main sequence star that is about 350 degrees cooler than the Sun. On the Hertzsprung-Russell diagram (left), the star lies slightly above the main sequence. This is because the star is very metal-rich; with an Fe/H of 0.3 dex the star has about twice the solar abundance of iron, which makes HD 154088 fall into the somewhat vague group of
5310232
Am star


visual magnitude. A small number of Am stars show unusually late spectral types and particularly strong luminosity effects. Although Am stars in general show abnormal luminosity effects, stars such as ρ Puppis are believed to be more evolved and more luminous than most Am stars, lying above the main sequence. Am stars and δ Scuti variables lie in approximately the same location on the H–R diagram, but it is rare for a star to be both an Am star and a δ Scuti variable. ρ Puppis is one example and δ
19790743
Bahcall–Wolf cusp


objects will have "ρ" formula_4 "r". If the less massive stars dominate the total density, their density will follow the Bahcall–Wolf form, whereas the more-massive stars will follow "ρ" formula_4 "r". In an old stellar population, most of the mass is either in the form of main-sequence stars, with masses formula_6 1–2 Solar masses, or in black hole remnants, with masses ~ 10–20 Solar masses. It is likely that the main-sequence stars dominate the total
16468400
Subgiant


. The end of the subgiant branch is defined to be when the core becomes degenerate or when the luminosity starts to increase. In general, stars with lower metallicity are smaller and hotter than stars with higher metallicity. For subgiants, this is complicated by different ages and core masses at the main sequence turnoff. Low metallicity stars develop a larger helium core before leaving the main sequence, hence lower mass stars show a hook at the start of the subgiant branch. The helium core mass of a Z=0.001 (extreme population II)
18305096
Beta Cassiopeiae


of variable includes subgiant or main sequence stars of spectral classes F5–A0, having masses between 1.5–2.5 solar masses and nearing the end of their core hydrogen fusion lifetime. Their pulsations are related to the same helium instability strip on the Hertzsprung–Russell diagram as that of classical Cepheids. Delta Scuti stars are located at the intersection of the strip with the main sequence. This star is rotating at about 92% of its critical speed, completing 1.12 rotations every day. This is giving the star an oblate spheroid shape with an equatorial bulge
12407220
Star formation


jets are produced called Herbig–Haro objects. This is probably the means by which excess angular momentum of the infalling material is expelled, allowing the star to continue to form. When the surrounding gas and dust envelope disperses and accretion process stops, the star is considered a pre-main-sequence star (PMS star). The energy source of these objects is gravitational contraction, as opposed to hydrogen burning in main sequence stars. The PMS star follows a Hayashi track on the Hertzsprung–Russell (H–R)
73796
Messier 43


. It is part of the much larger Orion Molecular Cloud Complex. The main ionizing star in this nebula is HD 37061 (variable star designation NU Ori), which is positioned near the center of the H II region and located from the Sun. This is a triple star system with the brighter component being a single-lined spectroscopic binary. The main component is a blue-white hued B-type main-sequence star with a stellar classification of B0.5V or B1V. It has times the mass of the Sun and times
7544319
Canopus


classified as F0Ib (Ib referring to "less luminous supergiant") on account of its high luminosity, or F0II. Its position in the H–R diagram indicates that it is a massive giant star currently in the core-helium burning phase. This is an intermediate mass star that has left the red-giant branch and has entered a blue loop with a significantly increased effective temperature, which has been measured to be 6,998 K. Very-long-baseline interferometry has been used to calculate its angular diameter at 6.9 mas
9253818
Pre-main-sequence star


too quickly as protostars. By the time they become visible, the hydrogen in their centers is already fusing and they are main-sequence objects. The energy source of PMS objects is gravitational contraction, as opposed to hydrogen burning in main-sequence stars. In the Hertzsprung–Russell diagram, pre-main-sequence stars with more than 0.5 first move vertically downward along Hayashi tracks, then leftward and horizontally along Henyey tracks, until they finally halt at the main sequence. Pre-main-sequence stars with less than
18679333
Subgiant


they age and broadens the main sequence band in the Hertzsprung–Russell diagram. Once a main sequence star ceases to fuse hydrogen in its core, the core begins to collapse under its own weight. This causes it to increase in temperature and hydrogen fuses in a shell outside the core, which provides more energy than core hydrogen burning. Low- and intermediate-mass stars expand and cool until at about 5,000 K they begin to increase in luminosity in a stage known as the red-giant branch. The transition from the main
18305084
Star cluster


distances to be measured using parallax. A Hertzsprung–Russell diagram can be plotted for these clusters which has absolute values known on the luminosity axis. Then, when similar diagram is plotted for a cluster whose distance is not known, the position of the main sequence can be compared to that of the first cluster and the distance estimated. This process is known as main-sequence fitting. Reddening and stellar populations must be accounted for when using this method. Nearly all stars in the Galactic field, including the Sun, were
9000706
Red-giant branch


identified early in the 20th century when the use of the Hertzsprung–Russell diagram made it clear that there were two distinct types of cool stars with very different sizes: dwarfs, now formally known as the main sequence; and giants. The term "red-giant branch" came into use during the 1940s and 1950s, although initially just as a general term to refer to the red-giant region of the Hertzsprung–Russell diagram. Although the basis of a thermonuclear main-sequence lifetime, followed by a thermodynamic contraction
8376372
Stellar isochrone


In stellar evolution, an isochrone is a curve on the Hertzsprung-Russell diagram, representing a population of stars of the same age. The Hertzsprung-Russell diagram plots a star's luminosity against its temperature, or equivalently, its color. Stars change their positions on the HR diagram throughout their life. Newborn stars of low or intermediate mass are born cold but extremely luminous. They contract and dim along the Hayashi track, decreasing in luminosity but staying at roughly the same temperature, until reaching the main sequence directly or by
6974388
Silicon-burning process


In astrophysics, silicon burning is a very brief sequence of nuclear fusion reactions that occur in massive stars with a minimum of about 8-11 solar masses. Silicon burning is the final stage of fusion for massive stars that have run out of the fuels that power them for their long lives in the "main sequence" on the Hertzsprung-Russell diagram. It follows the previous stages of hydrogen, helium, carbon, neon and oxygen burning processes. Silicon burning begins when gravitational contraction raises the star's core temperature to 2.7–3.5
3839591
Astrophysical X-ray source


There is an apparent X-ray "dividing line" in the H-R diagram among the giant stars as they cross from the main sequence to become red giants. Alpha Trianguli Australis (α TrA / α Trianguli Australis) appears to be a Hybrid star (parts of both sides) in the "Dividing Line" of evolutionary transition to red giant. α TrA can serve to test the several Dividing Line models. There is also a rather abrupt onset of X-ray emission around spectral type A7-F0, with a
6492237
Main sequence


dominant energy production process and the excess energy gained from gravitational contraction has been lost, the star lies along a curve on the Hertzsprung–Russell diagram (or HR diagram) called the standard main sequence. Astronomers will sometimes refer to this stage as "zero age main sequence", or ZAMS. The ZAMS curve can be calculated using computer models of stellar properties at the point when stars begin hydrogen fusion. From this point, the brightness and surface temperature of stars typically increase with age. A star remains near its initial
19833914
Main sequence


Above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of carbon, nitrogen and oxygen as intermediaries in the CNO cycle that produces helium from hydrogen atoms. Main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. Below this mass, stars have cores that are entirely radiative with convective zones near the surface. With decreasing stellar mass, the proportion of
19833903
Visual binary


main-sequence stars. This equation and the usual value of a = 3.5 only applies to main-sequence stars with masses 2"M"  "M"  20"M" and does not apply to red giants or white dwarfs. For these stars, the equation applies with different constants, since these stars have different masses. For the different ranges of masses, an adequate form of the Mass-Luminosity Relation is The greater a star's luminosity, the greater its mass will be. The absolute magnitude or luminosity of a star can
9241877
Main sequence


In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or dwarf stars. These are the most numerous true stars in the universe, and include the Earth's Sun. After condensation and ignition of a star, it generates thermal energy in its dense core region through
19833900
V509 Cassiopeiae


a ZAMS star show it crossing the "yellow evolutionary void" instability region first towards cooler temperatures, then later back towards hotter temperatures. The yellow evolutionary void is named because very few stars are found in that part of the H–R diagram. This is likely to be because the evolution of stars with such parameters is extremely rapid, perhaps even almost instant in astronomical terms. The first crossing of the yellow evolutionary void is very rapid but the star does not experience major instability. The second crossing, returning to hotter
21897557
HD 41742/41700


stars lie slightly below the main sequence on the Hertzsprung–Russell diagram (left image), which is probably due to their sub-solar metallicity (Fe/H ≈ −0.2). HD 41742 B is a much cooler star than the brighter components; its B-V indicates a spectral type of K3, making it approximately 1000 K cooler than the Sun. It lies on the main sequence on the HRD (left image), and its photometry is fully consistent with an dwarf. Indication of a young age for
17545342
Blue straggler


A blue straggler is a main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main sequence turnoff point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3. Standard theories of stellar evolution hold that the position of a star on the Hertzsprung–Russell diagram should be determined almost entirely by the initial mass of the star and its age. In a cluster, stars all formed at approximately the same
227734
Color–color diagram


studying color-color outliers in cases where one member is off the main sequence. The stages of the evolution of stars along the asymptotic giant branch from carbon star to planetary nebula appear on distinct regions of color–color diagrams. Quasars also appear as color-color outliers. Color–color diagrams are often used in infrared astronomy to study star forming regions. Stars form in clouds of dust. As the star continues to contract, a circumstellar disk of dust is formed, and this dust is heated by the star inside
5762727
Red giant


before it is dense enough to be degenerate, so helium fusion will begin much more smoothly, and produce no helium flash. The core helium fusing phase of a star's life is called the horizontal branch in metal-poor stars, so named because these stars lie on a nearly horizontal line in the H–R diagram of many star clusters. Metal-rich helium-fusing stars instead lie on the so-called red clump in the H–R diagram. An analogous process occurs when the central helium is exhausted
6522558
Hayashi track


follows the Hayashi track downwards, becoming several times less luminous but staying at roughly the same surface temperature, until either a radiative zone develops, at which point the star starts following the Henyey track, or nuclear fusion begins, marking its entry onto the main sequence. The shape and position of the Hayashi track on the Hertzsprung–Russell diagram depends on the star's mass and chemical composition. For solar-mass stars, the track lies at a temperature of roughly 4000 K. Stars on the track are nearly fully convective and
22151856
Giant star


the most obvious grouping of stars after the main sequence on most HR diagrams, although white dwarfs are more numerous but far less luminous. Examples: Giant stars with intermediate temperatures (spectral class G, F, and at least some A) are called yellow giants. They are far less numerous than red giants, partly because they only form from stars with somewhat higher masses, and partly because they spend less time in that phase of their lives. However, they include a number of important classes of variable stars. High
11942428
Giant star


whereas stars can spend much longer on the horizontal branch. Horizontal-branch stars, with more heavy elements and lower mass, are more unstable. Examples: The hottest giants, of spectral classes O, B, and sometimes early A, are called blue giants. Sometimes A- and late-B-type stars may be referred to as white giants. The blue giants are a very heterogeneous grouping, ranging from high-mass, high-luminosity stars just leaving the main sequence to low-mass, horizontal-branch
11942430
Stellar core


range of the M-type main-sequence stars, or red dwarf. The VLMS form the primary stellar component of the Milky Way at over 70% of the total population. The low mass end of the VLMS range reaches about , below which ordinary (non-deuterium) hydrogen fusion does not take place and the object is designated a brown dwarf. The temperature of the core region for a VLMS decreases with decreasing mass, while the density increases. For a star with , the core temperature is about while the
12324298
Mimosa (star)


-type stars. It is generating a strong stellar wind and is losing about per year, or the equivalent of the mass of the Sun every 100 million years. The wind is leaving the system with a velocity of 2,000 km s or more. The secondary, β Crucis B, may be a main sequence star with a stellar class of B2. In 2007, a third companion was announced, which may be a low mass, pre-main sequence star. The X-ray emission from this star was detected
21914708
O-type star


or supergiants, they continue to burn hydrogen in their cores for several million years and develop in a very different manner from low-mass stars such as the Sun. Most O-type main-sequence stars will evolve more or less horizontally in the HR diagram to cooler temperatures, becoming blue supergiants. Core helium ignition occurs smoothly as the stars expand and cool. There are a number of complex phases depending on the exact mass of the star and other initial conditions, but the lowest mass O-type stars will eventually
18811704
O-type star


short lifetimes, they are thought to be normal stages in the evolution of common stars only a little more massive than the Sun. O-type main-sequence stars are fueled by nuclear fusion, as all main-sequence stars are. However, the high mass of O-type stars results in extremely high core temperatures. At these temperatures, hydrogen fusion with the CNO cycle dominates the production of the star's energy and consumes its nuclear fuel at a much higher rate than low-mass stars which fuse hydrogen predominantly
18811700
Planetary habitability


biosphere to develop. Massive stars are thus eliminated as possible abodes for life. However, a massive-star system could be a progenitor of life in another way – the supernova explosion of the massive star in the central part of the system. This supernova will disperse heavier elements throughout its vicinity, created during the phase when the massive star has moved off of the main sequence, and the systems of the potential low-mass stars (which are still on the main sequence) within the former massive-star system may
7511760
Main sequence


outer region. By contrast, cool, very low-mass stars (below 0.4 ) are convective throughout. Thus the helium produced at the core is distributed across the star, producing a relatively uniform atmosphere and a proportionately longer main sequence lifespan. As non-fusing helium ash accumulates in the core of a main-sequence star, the reduction in the abundance of hydrogen per unit mass results in a gradual lowering of the fusion rate within that mass. Since it is the outflow of fusion-supplied energy that supports the
19833932
Star


convection will occur, forming a convection zone. This can occur, for example, in regions where very high energy fluxes occur, such as near the core or in areas with high opacity (making radiatative heat transfer inefficient) as in the outer envelope. The occurrence of convection in the outer envelope of a main sequence star depends on the star's mass. Stars with several times the mass of the Sun have a convection zone deep within the interior and a radiative zone in the outer layers. Smaller stars such as the
7029878
Main sequence


. This is suitable for stars at least as massive as the Sun, exhibiting the CNO cycle, and gives the better fit "R" ∝ "M". The table below shows typical values for stars along the main sequence. The values of luminosity ("L"), radius ("R") and mass ("M") are relative to the Sun—a dwarf star with a spectral classification of G2 V. The actual values for a star may vary by as much as 20–30% from the
19833923
Stellar core


the mass exceeds that limit, the core collapses and the outer layers of the star expand rapidly to become a red giant. In stars up to approximately , this occurs only a few million years after the star becomes a subgiant. Stars more massive than have cores above the Schönberg–Chandrasekhar limit before they leave the main sequence. Once the supply of hydrogen at the core of a low mass star with at least is depleted, it will leave the main sequence and evolve along the red giant branch of the Hertzsprung–Russell
12324305
Astronomical object


hierarchical organization. A planetary system and various minor objects such as asteroids, comets and debris, can form in a hierarchical process of accretion from the protoplanetary disks that surrounds newly formed stars. The various distinctive types of stars are shown by the Hertzsprung–Russell diagram (H–R diagram)—a plot of absolute stellar luminosity versus surface temperature. Each star follows an evolutionary track across this diagram. If this track takes the star through a region containing an intrinsic variable type, then its physical properties can cause it to become a variable
5133
AM Canum Venaticorum star


after mass transfer is started, and we should typically observe the binary after the period minimum. The third type of potential donor in an AM CVn system is the evolved main-sequence star. In this case, the secondary star does not cause a common envelope, but fills its Roche lobe near the end of the main sequence (terminal-age main sequence or "TAMS"). An important ingredient for this scenario is magnetic braking, which allows efficient angular-momentum loss from the orbit and hence a strong shrinkage
20730282
Radiation zone


ions. This leads to a violation of the stability criterion and to the creation of the convection zone; in the sun, opacity increases by more than a tenfold across the radiation zone, before the transition to the convection zone happens. Additional situations in which this stability criterion is not met are: For main sequence stars—those stars that are generating energy through the thermonuclear fusion of hydrogen at the core, the presence and location of radiative regions depends on the star's mass. Main sequence stars below about 0.3 solar masses
2880394
Red dwarf


of their hydrogen before leaving the main sequence. As a result, red dwarfs have estimated lifespans far longer than the present age of the universe, and stars less than have not had time to leave the main sequence. The lower the mass of a red dwarf, the longer the lifespan. It is believed that the lifespan of these stars exceeds the expected 10-billion-year lifespan of our Sun by the third or fourth power of the ratio of the solar mass to their masses; thus, a red dwarf may continue burning
11476482
ADS 9731


F4V and F5V and 1.35 and 1.32 solar masses respectively, which orbit each other every 3.27 days. This pair is in a 450-year orbit with star B, a star of spectral type G4V that has around the same mass as the Sun. Star C is a yellow white star of spectral type F3V around 1.41 times as massive as the sun, which has just started brightening and moving off the main sequence. It is in a 1000-year orbit with a pair of stars, Da and Db, a yellow-white main sequence
14339225
Main sequence


consumed during the main-sequence lifetime. The outer regions of a massive star transport energy by radiation, with little or no convection. Intermediate-mass stars such as Sirius may transport energy primarily by radiation, with a small core convection region. Medium-sized, low-mass stars like the Sun have a core region that is stable against convection, with a convection zone near the surface that mixes the outer layers. This results in a steady buildup of a helium-rich core, surrounded by a hydrogen-rich
19833931
Betelgeuse


on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks." Moreover, if future research bears out this hypothesis, Betelgeuse may prove to have traveled close to 200,000 AU as a red supergiant scattering as much as along its trajectory. Betelgeuse is a red supergiant that has evolved from an O-type main sequence star. Its core will eventually collapse, producing a supernova explosion and leaving behind a compact remnant. The details depend on the exact initial mass and other physical properties of that
9242017
Hayashi track


. The endpoints of each track lie on the main sequence. The horizontal segments for higher-mass stars show the Henyey track. It is approximately true that: The diagram to the right shows how Hayashi tracks change with changes in chemical composition. Z is the star's metallicity, the mass fraction not accounted for by hydrogen or helium. For any given hydrogen mass fraction, increasing Z leads to increasing molecular weight. The dependence of temperature on molecular weight is extremely steep—it is approximately Decreasing Z by a factor of
22151880
Red dwarf


occurs because of opacity of the interior, which has a high density compared to the temperature. As a result, energy transfer by radiation is decreased, and instead convection is the main form of energy transport to the surface of the star. Above this mass, a red dwarf will have a region around its core where convection does not occur. Because low-mass red dwarfs are fully convective, helium does not accumulate at the core, and compared to larger stars such as the Sun, they can burn a larger proportion
11476481
Star


plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram (H–R diagram). Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined. A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, releasing energy in the process
7029780
Hertzsprung–Russell diagram


the tip of the red giant branch stars. Contemplation of the diagram led astronomers to speculate that it might demonstrate stellar evolution, the main suggestion being that stars collapsed from red giants to dwarf stars, then moving down along the line of the main sequence in the course of their lifetimes. Stars were thought therefore to radiate energy by converting gravitational energy into radiation through the Kelvin–Helmholtz mechanism. This mechanism resulted in an age for the Sun of only tens of millions of years, creating a conflict over the age of the
10477977
Sh2-264


Sharpless 264, also known as the Lambda Orionis Ring, is a molecular cloud and H II region, which can be seen in the northern region of the Orion Molecular Cloud Complex (OMCC), in the constellation of Orion. The OMCC is one of the best-known star formation regions and the closest sector of the Milky Way to our Solar System where high-mass stars are born. The nebula is named after its main star, λ Orionis, a blue giant responsible for the ionization of the surrounding material.
6311617
Wolf–Rayet star


loss is influenced by a star's rotation rate, especially strongly at low metallicity. Fast rotation contributes to mixing of core fusion products through the rest of the star, enhancing surface abundances of heavy elements, and driving mass loss. Rotation causes stars to remain on the main sequence longer than non-rotating stars, evolve more quickly away from the red supergiant phase, or even evolve directly from the main sequence to hotter temperatures for very high masses, high metallicity or very rapid rotation. Stellar mass loss produces a loss of
7322001
T Tauri star


System would be one means by which the angular momentum of the contracting Sun was transferred to the protoplanetary disc and hence, eventually to the planets. Analogs of T Tauri stars in the higher mass range (2–8 solar masses)—A and B spectral type pre–main-sequence stars, are called Herbig Ae/Be-type stars. More massive (8 solar masses) stars in pre–main sequence stage are not observed, because they evolve very quickly: when they become visible (i.e. disperses surrounding circumstellar gas and dust cloud
14145010
Aldebaran b


likely to be around , as it is strongly irradiated by its giant host star. Nevertheless, when Aldebaran was a main sequence star, it is likely that the planet had an equilibrium temperature comparable to that of the Earth. The host star, Aldebaran, is an orange giant star, meaning it has moved off from the main sequence and exhausted the supply of hydrogen in the core. It has a spectral class of K5 III. Aldebaran is a K-type star that is 1.16 ± 0.07 times the mass and 44
19586263
Main sequence


are old enough for this to have occurred. In stars more massive than , the hydrogen surrounding the helium core reaches sufficient temperature and pressure to undergo fusion, forming a hydrogen-burning shell and causing the outer layers of the star to expand and cool. The stage as these stars move away from the main sequence is known as the subgiant branch; it is relatively brief and appears as a gap in the evolutionary track since few stars are observed at that point. When the helium core of low-mass stars becomes degenerate
19833946
Algol variable


Algol variables or Algol-type binaries are a class of eclipsing binary stars that are related to the prototype member of this class, β Persei (Beta Persei, Algol) from an evolutionary point of view. An Algol binary is a semidetached binary system where the primary component is an early type, main sequence star that does not fill its Roche lobe, while the cooler, fainter, larger, less massive secondary component lies above the main sequence in a Hertzsprung–Russell diagram and fills the Roche lobe. Early in its
17926935