This is a list of the most massive stars so far discovered, in solar masses (M☉).
Most of the masses listed below are contested and, being the subject of current research, remain under review and subject to revision. Indeed, many of the masses listed in the table below are inferred from theory, using difficult measurements of the stars’ temperatures and absolute brightnesses. All the listed masses are uncertain: both the theory and the measurements are pushing the limits of current knowledge and technology. Either measurement or theory, or both, could be incorrect. For example, VV Cephei could be between 25–40 M☉, or 100 M☉, depending on which property of the star is examined.
Massive stars are rare; astronomers must look very far from the Earth to find one. All the listed stars are many thousands of light years away and that alone makes measurements difficult. In addition to being far away, many stars of such extreme mass are surrounded by clouds of outflowing gas created by powerful stellar winds; the surrounding gas interferes with the already difficult-to-obtain measurements of stellar temperatures and brightnesses and greatly complicates the issue of estimating internal chemical compositions. For some methods, different determinations of chemical composition lead to different estimates of mass. In addition, the clouds of gas make it difficult to judge whether the star is just a single supermassive object or, instead, a multiple star system. A number of the "stars" listed below may actually consist of two or more companions in close orbit, each star being massive in itself but not necessarily supermassive. Other combinations are possible – for example a supermassive star with one or more smaller companions or more than one giant star. Without being able to see inside the surrounding cloud, it is difficult to know the truth of the matter. More globally, statistics on stellar populations seem to indicate that the upper mass limit is in the 100–200 solar mass range.
Amongst the most reliable listed masses are those for the eclipsing binaries NGC 3603-A1, WR21a, and WR20a. Masses for all three were obtained from orbital measurements – for a binary star, it is possible to measure the individual masses of the two stars by studying their orbital motions, using Kepler's laws of planetary motion. This involves measuring their radial velocities and also their light curves. The radial velocities only yield minimum values for the masses, depending on inclination, but light curves of eclipsing binaries provide the missing information: inclination of the orbit to our line of sight. Therefore, eclipsing binaries are the only stars whose masses are derived with some confidence.
However note that almost all of the masses listed in the table below were inferred by indirect methods; only a few masses were determined using eclipsing systems.
Some stars may once have been heavier than they are today. It is likely that many have suffered significant mass loss, perhaps as much as several tens of solar masses, expelled by the process of superwind, where high velocity winds are expelled from the hot photosphere into interstellar space. This process is similar to superwinds generated by Asymptotic Giant Branch (AGB) stars in form red giants or planetary nebulae. The process forms an enlarged extended envelope around the star that interacts with the nearby interstellar medium and infusing the region with element heavier than Hydrogen or Helium.
There are also – or rather were – stars that might have appeared on the list but no longer exist as stars or are supernova impostors. Today we see only the debris (see for example hypernovae and supernova remnant). The masses of the precursor stars that fueled these cataclysms can be estimated from the type of explosion and the energy released, but those masses are not listed here.
The following is a list of a few stars with an estimated mass of 25 M☉ or greater, including the stars of Arches cluster, Cygnus OB2 cluster, Pismis 24 cluster, and R136 cluster. Note that all O-type stars have masses greater than 15 M☉ and catalogs of such stars (GOSS, Reed) list hundreds of cases.
The majority of stars thought to be more than 100 M☉ are shown, but this list is far from complete – especially below 80 M☉. The method used to determine the mass is included in the list to give an idea of uncertainty: direct methods (binary stars) being more secure than indirect ones (conversion from luminosity, extrapolation from stellar atmosphere models, ...).
The masses listed below are the stars’ current (evolved) mass, not their initial (formation) mass.
Wolf–Rayet star |
Luminous blue variable star |
O-class star |
B-class star |
Hypergiant |
Star name | Mass (M☉, Sun = 1) |
Distance from earth (ly) | Method used to estimate mass | Refs. |
---|---|---|---|---|
R136a1 | 315 | 163,000 | Evolutionary model | [1] |
R136c | 230 | 163,000 | Evolutionary model | [1] |
BAT99-98 | 226 | 165,000 | Luminosity/Atmosphere model | [2] |
R136a2 | 195 | 163,000 | Evolutionary model | [1] |
Melnick 42 | 189 | 163,000 | Luminosity/Atmosphere model | [3] |
R136a3 | 180 | 163,000 | Evolutionary model | [1] |
Melnick 34 | 179 | 163,000 | Luminosity/Atmosphere model | [4] |
HD 15558 A | >152 ± 51 | 24,400 | Binary | [5][6] |
VFTS 682 | 150 | 164,000 | Luminosity/Atmosphere model | [7] |
R136a6 | 150 | 157,000 | Evolutionary model | [1] |
LH 10-3209 A | 140 | ? | [8] | |
NGC 3603-B | 132 ± 13 | 24,700 | Luminosity/Atmosphere model | [9] |
HD 269810 | 130 | Luminosity/Atmosphere model | [10] | |
P871 | 130 | ? | [8] | |
WR 42e | 125–135 | 25,000 | Ejection in triple system | [11][a] |
R136a4 | 124 | 157,000 | Evolutionary model | [1] |
Arches-F9 | 111–131 | 25,000 | Luminosity/Atmosphere model | [12] |
NGC 3603-A1a | 120 | 24,700 | Eclipsing binary | [9] |
LSS 4067 | 120 | Evolutionary model | [13] | |
NGC 3603-C | 113 ± 10 | 22,500 | Luminosity/Atmosphere model | [9] |
Cygnus OB2-12 | 110 | 5,220 | Luminosity/Atmosphere model | [14] |
WR 25 | 110 | 10,500 | Binary? | |
HD 93129 A | 110 | 7,500 | Luminosity/Atmosphere model | |
Arches-F1 | 101–119 | 25,000 | Luminosity/Atmosphere model | [12] |
Arches-F6 | 101–119 | 25,000 | Luminosity/Atmosphere model | [12] |
WR21a A | 103.6 | 26,100 | Binary | [15] |
BAT99-33 (R99) | 103 | 16,400 | Luminosity/Atmosphere model | [2] |
R136a5 | 101 | 157,000 | Evolutionary model | [1] |
η Carinae A | 100 - 200 | 7,500 | Luminosity/Binary | [16][17] |
Peony Star (WR 102ka) | 100 | 26,000 | Luminosity/Atmosphere model? | [18] |
Cygnus OB2 #516 | 100 | 4,700 | Luminosity? | |
Sk -68°137 | 99 | ? | [8] | |
R136a8 | 96 | 157,000 | Evolutionary model | [1] |
HST-42 | 95 | ? | [8] | |
P1311 | 94 | ? | [8] | |
Sk -66°172 | 94 | ? | [8] | |
Arches-F7 | 86–102 | 25,000 | Luminosity/Atmosphere model | [12] |
R136b | 93 | 163,000 | Evolutionary model | [1] |
NGC 3603-A1b | 92 | 24,800 | Eclipsing binary | [9] |
HST-A3 | 91 | ? | [8] | |
HD 38282 B | >90 | Luminosity | [19] | |
Cygnus OB2 #771 | 90 | Luminosity/Atmosphere model? | ||
Arches-F15 | 80–97 | Luminosity/Atmosphere model | [12] | |
HSH95 31 | 87 | Evolutionary model[1] | ||
HD 93250 | 86.83 | Luminosity/Atmosphere model | [20] | |
LH 10-3061 | 85 | ? | [8] | |
BI 253 | 84 | |||
WR20a A | 82.7 ± 5.5 | Eclipsing binary | [21] | |
MACHO 05:34-69:31 | 82 | ? | [8] | |
WR20a B | 81.9 ± 5.5 | Eclipsing binary | [21] | |
NGC 346-3 | 81 | ? | [8] | |
HD 38282 A | >80 | Luminosity | [19] | |
Sk -71 51 | 80 | Luminosity | [22] | |
Cygnus OB2-8B | 80 | Luminosity? | ||
WR 148 | 80 | ? | [23] | |
HD 97950 | 80 | ? |
A few additional examples with masses lower than 80 M☉.
Star name | Mass (M☉, Sun = 1) |
Method | Refs. |
---|---|---|---|
R139 A | 78 | [24] | |
V429 Carinae A | 78 | ||
WR 22 | 78 | ||
Pismis 24-17 | 78 | [25] | |
Cygnus OB2-11 | 73+32 −24 |
[26] | |
Arches-F12 | 70–82 | ||
Arches-F18 | 67–82 | ||
Var 83 in M33 | 60–85 | ||
Arches-F4 | 66–76 | ||
Arches-F28 | 66–76 | ||
R126 | 70 | ||
Companion to M33 X-7 | 70 | [27] | |
BD+43° 3654 | 70 | ||
HD 93205 | 69 | [8] | |
R136a7 | 69 | Evolutionary model[1] | |
HD 93403 A | 68.5 | ||
HD 5980 B | 66 | ||
HD 5980 A | 61 | ||
BAT99-119 (R145) | 53+20 −40 + 54+20 −40 |
Binary | [28][b] |
Arches-F21 | 56–70 | ||
Arches-F10 | 55–69 | ||
AG Carinae | 55 | ||
Arches-F14 | 54–65 | ||
S Monocerotis | 59 | ||
WR21a B | 58.3 | [15] | |
WR 102ea | 58 | [29] | |
Arches-F3 | 52–63 | ||
CD Crucis A | 57 | [30] | |
Arches-B1 | 50–60 | ||
HD 16691 | 56.6 | ||
ζ Puppis (Naos) | 56.1 | ||
Plaskett's star B | 56 | ||
9 Sagittarii A | 55 | ||
η Carinae B | 30-80 | Luminosity/Binary [17] | |
BD+40° 4210 | 54 | ||
Plaskett's star A | 54 | ||
HD 93129 B | 52 | [31] | |
Cygnus OB2-4 | 52 | ||
Arches-F20 | 47–57 | ||
LH54-425 | A=47 ± 2, B=28 ± 1 | Binary[32] | [32] |
Arches-F16 | 46–56 | ||
WR 102c | 45–55 | [18] | |
CD Crucis B | 48 | [30] | |
Arches-F8 | 43–51 | ||
Sher 25 in NGC 3603 | 40–52 | ||
Arches-F2 | 42–49 | ||
HD 15558 B | 45 ± 11 | [5][6] | |
S Doradus | 45 | ||
HD 50064 | 45 | ||
WR 141 | 45 | [23] | |
IRS-8* | 44.5 | [33] | |
Cygnus OB2-8A A | 44.1 | ||
Cygnus OB2-1 | 44 | ||
Cygnus OB2-10 | 43.1±14 | [26] | |
α Camelopardalis | 43 | ||
Pismis 24-2 | 43 | ||
χ2 Orionis | 42.3 | ||
Cygnus OB2-8C | 42.2±14 | [26] | |
Cygnus OB2-6 | 42 | ||
ε Orionis (Alnilam) | 30-64.5[34] | ||
θ1 Orionis C | 40 | ||
μ Nor | 40 | ||
Cygnus OB2-7 | 39.7+17 −10 |
[26] | |
Companion to NGC 300 X-1 | 38 | [35] | |
Pismis 24-16 | 38 | ||
Pismis 24-25 | 38 | ||
Cygnus OB2-8A B | 37.4 | ||
HD 93403 B | 37.3 | ||
ζ1 Scorpii | 36 | ||
Pismis 24-13 | 35 | ||
Companion to IC 10 X-1[36] | 35 | ||
Cygnus OB2-9 A | >34 | ||
Arches-F5 | 31–36 | ||
Cygnus OB2-18 | 33 | ||
ζ Orionis (Alnitak) | 33 | ||
19 Cephei | 30–35 | ||
ξ Persei | 26–36 | ||
Cygnus OB2-5 A | 31 | ||
Cygnus OB2-9 B | >30 | ||
γ Velorum A (Regor A) | 30 | ||
P Cygni | 30 | ||
VFTS 352 | A=28.63 ± 0.3, B=28.85 ± 0.3 | [37] | |
The Pistol Star (V4647 Sgr) | 27.5 | ||
10 Lacertae | 26.9 | ||
6 Cassiopeiae | 25 | [38] | |
Pismis 24-3 | 25 | ||
NGC 7538 S | 25 | [39] | |
VFTS 102 | 25 | ||
ρ Cassiopeiae | 14–30 |
Black holes are the end point evolution of massive stars. Technically they are not stars, as they no longer generate heat and light via nuclear fusion in their cores.
The limit on mass arises because stars of greater mass have a higher rate of core energy generation, their luminosity increasing far out of proportion to their mass. For a sufficiently massive star the outward pressure of radiant energy generated by nuclear fusion in the star’s core exceeds the inward pull of its own gravity. This is called the Eddington limit. Beyond this limit, a star ought to push itself apart, or at least shed enough mass to reduce its internal energy generation to a lower, maintainable rate. In theory, a more massive star could not hold itself together because of the mass loss resulting from the outflow of stellar material. In practice the theoretical Eddington Limit must be modified for high luminosity stars and the empirical Humphreys-Davidson limit is derived.[40]
Astronomers have long theorized that as a protostar grows to a size beyond 120 M☉, something drastic must happen. Although the limit can be stretched for very early Population III stars, and although the exact value is uncertain, if any stars still exist above 150-200 M☉ they would challenge current theories of stellar evolution.
Studying the Arches cluster, which is currently the densest cluster of stars in our galaxy, astronomers have confirmed that stars in that cluster do not occur any larger than about 150 M☉. One theory to explain rare ultramassive stars that exceed this limit – for example in the R136 star cluster – is the collision and merger of two massive stars in a close binary system.[41]
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