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Stars

The Milky Way galaxy is made up of hundreds of billions of stars, spheres of plasma sustained by nuclear fusion and bound together by the enormity of their mass. The energy from the fusion of hydrogen into helium and helium into other, heavier elements produces heat and light, or electromagnetic radiation. Stars form the center of star systems, in which stars are orbited by planets and other astronomical objects, including other stars. A subset of stars known as Main Sequence stars produce hydrogen-rich coronae that ships can skim for fuel using a Fuel Scoop.

Stellar Classification

Each star or dwarf in Elite: Dangerous has an identifier for its classification which conforms to the Morgan–Keenan (MK) classification system.

For example, the Sun of Sol has the classification identifier: G2 V

Each identifier consists of three components:

  1. Spectral class: A capital letter out of the sequence: O, B, A, F, G, K, M. (A helpful real-world mnemonic for remembering this is, "Oh Be A Fine Girl, Kiss Me.") This mainly specifies the temperature ranging from O (hottest) to M (coolest). Other letters specify extensions to this classification system, namely: W (WN, WC, WO), L, T, Y, C, S, D. A few of those classes have subclasses such as DA, DB and DC as subclasses of D.
  2. Spectral subclass: Each letter class is then subdivided using a numeric digit with 0 being the hottest and 9 being the coolest.
  3. Luminosity class: A luminosity class is added to the spectral class using Roman numerals.This classifies the stars by its spectral characteristics considering color and brightness. Those spectral characteristics provide information about the type of the star:
  • I for supergiants
    • Ia or 0 for hypergiants or extremely luminous supergiants
    • Iab for normal supergiants
    • Ib for less luminous supergiants
  • II for bright giants
  • III for regular giants
  • IV for sub-giants
  • V for main-sequence stars (most of the known stars belong to this class)
    • Va for extremely luminous main sequence stars
    • Vab for luminous main sequence stars
    • Vb for normal main sequence stars
    • Vz for less luminous main sequence stars
  • VI for sub-dwarfs
  • VII for white dwarf

Thus, G2 V means: The Sun is semi hot (G), it belongs to the hotter stars (2) in class G and it is considered as a so called main-sequence star (V).

Star Types


Main Sequence Stars (O, B, A, F, G, K, M)

With a ratio of ~77%[1] of all stars this category can be considered Very Common.[2]

Image[3] Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
Class O star.png
O Yes Very Rare (~0.2%) Class O type stars are the most luminous and massive main sequence stars in the galaxy. They range in mass from 15 to 90 solar masses and burn very brightly indeed, with a surface temperature reaching 52,000 K so appear very blue. They are very short lived with lifetimes of 1 - 10 million years, ending in supernova.

Class O star systems rarely contain terrestrial bodies. One of the most likely to host a stellar nursery.

Class B star.png
B Yes Rare (~1.7%) Class B stars are very luminous blue-white stars. They range in mass from 2 to 16 solar masses and have a surface temperature reaching 30,000 K. Their lifetimes are shorter than most main sequence stars.

Class B star systems rarely contain terrestrial bodies. One of the most likely to host a stellar nursery.

A V HIP 99152.png
A Yes Uncommon (~6%) Class A stars are hot white or bluish white main sequence stars. They range in mass from 1.4 to 2.1 solar masses and have a surface temperature reaching 10,000 K.

Class A star systems often contain high metal content worlds and metal-rich bodies.

F9 Vb Wredguia ZF-F d11-23.png
F Yes Common (~12%) Class F stars are white main sequence stars. They range in mass from 1 to 1.4 solar masses and have a surface temperature reaching 7,600 K.

Class F star systems are one of the most likely to contain Earth-like worlds.

G4 Vab Wredguia AG-F d11-24 A.png
G Yes Common (~9%) Class G stars are white-yellow main sequence stars. They range in mass from 0.8 to 1.2 solar masses and have a surface temperature reaching 6,000 K.

Class G star systems are one of the most likely to contain Earth-like worlds.

K (Yellow-Orange) Star - Ross 1069 A.jpeg
K4 Va Wredguia HY-G c24-11 A.png
K Yes Common (~25%) Class K stars are yellow-orange main sequence stars with a long and generally stable life. They range in mass from 0.6 to 0.9 solar masses and have a surface temperature reaching 5,000 K.

Class K star systems are the most likely to contain water worlds and rocky bodies.

M6 Va Wredguia FP-R b46-1.png
M (Red dwarf) Star (2) - 2MASS J04414489+2301513.jpeg
M Yes Very Common (~46%)
Class M stars are red stars that form the bulk of the main sequence stars in the galaxy. Their mass is low, as is their surface temperature.

Class M star systems tend to contain many icy bodies and rocky ice worlds.

Giants and Supergiants

With a ratio of ~0.25%[1] of all stars this category can be considered Very Rare.[2]

Image[3] Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
Class B Blue-White Supergiant.png
Class B Supergiant Alt.png
B Blue-White Supergiant Yes Very Rare (~0.7%) Class B blue-white supergiant star. It is approaching the end of its life and hydrogen burning has stopped in its core. The star has begun expanding towards being a red supergiant.
Blue-White Supergiant (Type B).jpg
Class A supergiant.png
A Blue-White Supergiant Yes Uncommon (~9.2%) Class A blue-white supergiant star. It is approaching the end of its life and hydrogen burning has stopped in its core, and the star has begun expanding into a red supergiant.
F (White super giant) Star - HD 164684.jpeg
F White Supergiant Yes Rare (~2.1%) Class F white supergiant star. It is approaching the end of its life and hydrogen burning has stopped in its core, and the star has begun expanding into a red supergiant.
Class G White-Yellow Sueprgiant.png
G White-Yellow Supergiant Yes Rare (~1.6%) Class G yellow-white supergiant star. It is approaching the end of its life and hydrogen burning has stopped in its core, and the star has begun expanding towards being a red supergiant.
K7 III 35 Ursae Majoris.png
K Orange Giant Yes Common (~20%)
Orange giant stars with spectral type K. Orange giants like this are reaching the end of their lives, and have moved off the main sequence. Hydrogen has stopped fusing in the core, leaving a collapsed core of degenerate helium, and hydrogen burning is taking place in an outer shell as the star continues to expand.
M (Red giant) Star - Lambda Aquarii.jpeg
M Red Giant Yes Very Common (~64%)
Red giants are in the latter part of their lives. Hydrogen has stopped fusing in their degenerate helium cores and has moved to an outer shell, causing the star to expand. The outer atmosphere is inflated and tenuous, and the surface temperature is below 5,000 K.
M (Red super giant) Star - 35 Pi Aurigae A.jpeg
M Red Supergiant Yes Rare (~1.4%)
Red supergiants are massive stars near the end of their lives. They have entered a helium burning phase, where helium is fused into carbon and oxygen. they have enormous sizes swelling up to many hundred solar diameters - up to 7 AU in some cases. their out reaches can be quite cool - typically 3500-4500 K.

Proto Stars (Herbig Ae/Be, TTS)

With a ratio of ~2.4%[1] of all stars this category can be considered Rare.[2]

Image[3] Class[4] Fuel-Scoopable Rarity Within Type[5]

Description / Notes

Herbig Ae Be Star (1) - Dumboe AA-A h207 ABC 4.jpeg
Herbig Ae Be Star (2) - Ogaiws AA-A h188 A.jpeg
Herbig Ae/Be No Rare (~4%)
Herbig Ae/Be stars are young stars typically less than 10 million years old with characteristics of either A or B class main sequence stars. They are usually between 2 and 8 solar masses. The mass of the proto-star determines its spectral class when it joins the main sequence.

Herbig Ae/Be stars are more common nearer the galactic core.

TTS5 Vab Wredguia HY-G c24-12.png
TTS0 VI Col 285 Sector LU-K b10-3.png
TT4.png
TTS No Very Common (~96%)
T Tauri type stars are very young stars which are in the process of gravitational contraction.

Take caution when travelling and using a fuel scoop, as the TTS' appearance often resembles M or K stars.

Carbon Stars (C, CH, CHd, CJ, CN, CS, MS, S)

With a ratio of ~0.08%[1] of all stars this category can be considered Very Rare.[2]

Image[3] Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
C Star (1) - HIP 38242 A.jpeg
C Star (2) - HIP 22796 A.jpeg
C Star (3) - HIP 75691.jpeg
C Star (4) - 53 Aquarii.jpeg
C No Very Rare (~0.7%)
Carbon class stars are stars approaching the end of their life. A carbon star is a late-type star similar to a red giant (or occasionally to a red dwarf) whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "sooty" atmosphere and a strikingly ruby red appearance. The surface temperature is rarely higher than 4300 K.
CH No
CHd No
CJ Star - Lasuae RJ-X d2-574 A.jpeg
CJ No Rare (~3%)
C-J Class stars are variants of carbon class stars, stars that are approaching the end of their stellar lives as hydrogen fusion begins to stop. This CJ variant has much more carbon-13 in its atmosphere.
CN Star - Eorgh Prou CU-R d4-568 A.jpeg
CN No Common (~24%)
Class C-N stars are variants of carbon class stars, stars that are approaching the end of their stellar lives as hydrogen fusion begins to stop. They were once K or M type stars that have degenerated to the carbon phase of their life cycle.
CS No
MS-type Star - Dryipai XP-G d10-37 A.jpeg
MS No Very Common (~36%)
MS class stars are late sequence stars having progressed from the S class stage of their life cycle and heading towards becoming a carbon star, a star nearing the end of its stellar life.
S-type Star (1) - HIP 40977 A.jpeg
S-type Star (2) - HIP 96983 A.jpeg
S-type Star (3) - Boeph WY-S e3-890 C.jpeg
S No Very Common (~37%)
Class S stars are a late-type giant star (similar to class K5–M) whose spectrum displays bands from zirconium oxide, in addition to the titanium oxide bands characteristically exhibited by K and M class giant stars.

Wolf-Rayet Stars (W, WC, WNC, WNC, WO)

With a ratio of ~0.05%[1] of all stars this category can be considered Very Rare.[2]

Image Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
20160901141747 1.jpg
W No Very Rare (~0.44%)
Wolf-Rayet class stars are massive stars that are nearing the end of their life cycle and have moved out of their hydrogen-burning phase. They were once over 20 solar masses but now shed considerable amounts of material through solar wind. Their surface temperature can reach 200,000 K, so they appear a brilliant blue.
WC.jpg
WC No Common (~21%)
Wolf-Rayet class stars are massive stars that are nearing the end of their life cycle and have moved out of their hydrogen-burning phase. They were once over 20 solar masses but now shed considerable amounts of material through solar wind. Their surface temperature can reach 200,000 K, so they appear a brilliant blue. This star is a variant of the Wolf-Rayet stars whose spectrum is dominated by ionised carbon lines.
Wolf-Rayet N Star.jpg
WN No Common (~15%)
Wolf-Rayet class stars are massive stars that are nearing the end of their life cycle and moved out of their hydrogen-burning phase. They were once over 20 solar masses but now shed considerable amounts of material through solar wind. Their surface temperature can reach 200,000 K, so they appear a brilliant blue. This star is a variant of the Wolf-Rayet stars whose spectrum is dominated by ionised nitrogen and helium lines.
Wolf-Rayet NC Star.jpg
WNC No Common (~16%)
Wolf-Rayet class stars are massive stars that are nearing the end of their life cycle and have moved out of their hydrogen-burning phase. They were once over 20 solar masses but now shed considerable amounts of material through solar wind. Their surface temperature can reach 200,000 K, so they appear a brilliant blue. This star is a variant of the Wolf-Rayet stars whose spectrum is dominated by ionised nitrogen, carbon-oxygen and helium lines.
WO Wolf Rayet Class Star.png
WO No Very Common (~47%)
Wolf-Rayet class stars are massive stars that are nearing the end of their life cycle and have moved out of their hydrogen-burning phase. They were once over 20 solar masses but now shed considerable amounts of material through solar wind. Their surface temperature can reach 200,000 K, so they appear a brilliant blue. This star is a variant of the Wolf-Rayet stars whose spectrum is dominated by ionised helium, carbon and oxygen lines.

Black Holes

With a ratio of ~0.41%[1] of all stars this category can be considered Very Rare.[2]

Image Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
Black-Hole-Deep-Space.jpg
Black Hole No N/A Black holes are typically the stellar remnants of super massive stars of twenty solar masses or more, that have reached the end of their lives. Nuclear fusion has ceased, and the star collapsed to the most extreme point possible - where gravity is so extreme light itself can no longer escape. If matter should fall on to such a body, an extreme burst of gamma radiation will be emitted, but otherwise the body is only visible by the gravitational distortion in the vicinity. In many cases black holes can be seen emitting brightly in X-rays because of matter falling on to their surface from a companion body.

Less likely to be found nearer the edge of the galactic plane.

Sagittarius A.png
Supermassive Black Hole No Only 1 documented Supermassive Black Holes tend to form when an initial Black Hole begins to swallow even more mass including other Black Hole. With time they acquire a vast mass - and become a key compoment of the galaxy. With much of the other galactic mass rotating around them and can be several million solar masses.

Take great caution when approaching a supermassive black hole, as unlike other smaller black holes, a supermassive black hole will cause rapid heat build-up if approached too closely, causing significant ship damage. Sagittarius A* is currently the only known Supermassive Black Hole in the game.

Neutron Stars

With a ratio of ~4.0%[1] of all stars this category can be considered Rare.[2]

Image Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
Neutron-Star-in-Elite.png
Neutron Star No N/A
Neutron stars are the stellar remnants of massive stars that have reached the end of their lives. Once nuclear fusion was exhausted, the star collapsed into a tiny volume.
Because of its high mass, the matter has collapsed into Neutron-degenerate matter (sometimes called Neutronium), an extremely high density state made up entirely of neutrons (matter composed of stuff other than atoms, such as quarks, protons, neutrons or whatever, is referred to as "degenerate matter"). Unlike most degenerate matter where electrons are below the Fermi-Energy (chemical potential at T=0), the compression is so great that the Fermi-Energy of the electrons increases such that they combine with protons to form neutrons. As the star is in equilibrium, its gravity is balanced by 'neutron degeneracy pressure' (compressed neutron wave functions which are energetic due to the uncertainty principle), though with more mass the system's gravity would overcome the neutron degeneracy pressure forming a black hole. Degenerate matter stars are as dense as matter can possibly be without becoming a black hole.

Take caution when approaching these stars, as they are so tiny they are almost invisible. They still radiate heat, and getting closer than 0.25Ls will cause one's heat to build up. If you fly with your ship into the emitted energy cloud your FSD will be supercharged and the jump range for the next jump will be dramatically increased. However, dropping out of supercruise while within a neutron star's jet is incredibly dangerous, as incredibly fast particles of ionized matter will tear through your ship's hull and systems. Take special care when supercharging to ensure that you do not fly too close to the star, or your ship may be heavily damaged/destroyed after performing an emergency drop. More common near the center of the galaxy.

White Dwarfs (D, DA*, DB*, DC*, DO*, DQ, DX)

With a ratio of ~0.36%[1] of all stars this category can be considered Very Rare.[2]

White dwarfs (category D for degenerate) are the collapsed core of a star that has lost a large proportion (~20%) of its original mass as the ejected material of a planetary nebula or in a supernova explosion, the terminal stages of stellar evolution. White dwarfs are not stars because they no longer sustain nuclear fusion, and lacking this interior thermal source of support the star has gravitationally collapsed to a very small radius. White dwarfs glow with the residual heat of the degenerate core, which can have a temperature well above 100,000 K at collapse and that cools over several billion years. Class D is further divided into spectral types[6] that indicate the elemental composition of the photosphere.

  • DA: strong Balmer series hydrogen absorption lines only; no helium or metals present.
  • DB: strong He I (neutral helium) absorption lines only; no hydrogen or metals present.
  • DC: a continuous (blackbody) spectrum with no absorption lines deeper than 5% in any part of the electromagnetic spectrum.
  • DO: strong lines of He II (ionized helium) with molecular hydrogen or helium present.
  • DQ: carbon absorption lines, either atomic or molecular, in any part of the electromagnetic spectrum.
  • DZ: metal (elements heavier than helium) absorption lines in the absence of both hydrogen and helium lines.

Symbols Appended to the Above Designations

  • P: magnetic white dwarfs with detectable polarization.
  • H: magnetic white dwarfs without polarization.
  • X: peculiar or unclassifiable spectrum.
  • E: emission lines (of any element) present.
  •  ?, :: uncertain classification.
  • V: variable luminosity.
  • d: circumstellar dust.
  • C I, C II, O I, O II added within parentheses to indicate the presence of these elements in DQ objects.

The current practice is to append numerical indicators of the white dwarf temperature and surface gravity, separated by an underline "_". Temperature is indicated as the effective surface temperature divided into 50400 and rounded to the first decimal place, e.g. DA.9 = 56000 K and DB1.2 = 42000 K. Gravity is assessed as the width of the dominant spectral lines and the log values range from 7 to 9.

The table below shows the white dwarf subtypes within Elite Dangerous. These do not necessarily match the notation mentioned above (for example, ED uses DAZ which probably should be DZ) but comes very close. The "Rarity" column indicates the subtype rarity within the White Dwarfs spectrum.

Image Class[4] Authoring (mainly) Rarity Within Type[5] Description / Notes
D Manual Very Rare (~0.9%)
Class DA star.png
DA Procedural Common (~29%)
Class DA stars are white dwarf stars with a hydrogen rich atmosphere.

Take caution when approaching these stars, as their sphere of influence is surprisingly large for their size.

DAB (White Dwarf) Star.jpg
DAB Procedural Common (~12%) Class DAB stars are white dwarf stars with hydrogen and helium rich atmospheres and neutral helium emission lines.
DAO
DAV.jpg
DAV Procedural Rare (~3.2%)
DAV class stars are also known as pulsating white dwarfs as their luminosity changes according to non-radial gravity waves within the star. They have hydrogen rich atmospheres.
XPonM9J - Imgur.jpg
DAZ Procedural Very Rare (~0.43%) Class DAZ stars are white dwarfs which are hydrogen rich metallic stars.
DB (White Dwarf) Star.jpg
DB Procedural Uncommon (~5.1%)
Class DB stars are white dwarf stars with a helium rich atmosphere with neutral helium emission lines.
DBV Class Star.jpg
DBV Procedural Rare (~1.0%)
DBV class stars are known as pulsating white dwarfs as their luminosity changes according to non-radial gravity waves within the star. They have helium rich atmospheres.
DBZ Procedural Very Rare (~0.11%)
Class DBZ stars are helium rich and metallic white dwarf type stars.
DC (White Dwarf) Star.jpg
DC Procedural Very Common (~44%)
Class DC stars have a continuous (blackbody) spectrum with no absorption lines deeper than 5% in any part of the electromagnetic spectrum.
Class DCV Dwarf.png
DCV Procedural Rare (~3.8%)
Class DCV stars are white dwarfs with varying luminosity.
DO
DOV
DQ.png
DQ Manual Very Rare (0.02%)
Class DQ stars are white dwarfs with a carbon rich atmosphere.
DX

Brown Dwarfs (L, T, Y)

With a ratio of ~15% [1] of all stars this category can be considered Common.[2]

Image Class[4] Fuel-Scoopable Rarity Within Type[5] Description / Notes
L3 V Wredguia HY-G c24-10 B.png
L No Very Common (~58%)
Class L dwarfs are dwarf stars that are cooler than M class stars. They are on the borderline of supporting fusion of hydrogen in their cores, and their temperatures range from 1,300 to 2,400 K, cool enough to have alkaline metals and metal hydrides in their atmospheres.

Class L star systems tend to contain many icy bodies.

T3 V Wredguia HY-G c24-11 C.png
T No Common (~27%)
Class T dwarfs are brown dwarfs with a surface temperature between 700 and 1,300 K. They are sometimes known as Methane Dwarfs due to the prominence of methane in their composition. They are on the borderline between what might be considered a very large gas giant planet and a star.

Class T star systems tend to contain many icy bodies.

Y1 V Wredguia HY-G c24-10 D.png
Y1 V HIP 99152 1.png
Y No Common (~15%)
Class Y dwarfs are the coolest of brown dwarfs. Surface temperatures are less than 700 K, and are effectively very large gas giant planets, with some stellar properties.

Class Y star systems tend to contain many icy bodies. Take caution when exiting a hyperspace jump into a Y-Class star system, as the humble appearance of these star types can cause one to fly too close to the star, hitting the body exclusion zone and triggering an emergency drop from supercruise.

Undiscovered Star Types

These classes are mentioned in the Journal documentation,[4] but none have been submitted to EDSM yet.

Image Class[4] Fuel-Scoopable Rarity Within Type Description / Notes
Exotic None found/reported yet.
Nebula Some systems, when searched for in the galaxy map, will result in the selection of a correspondingly named nebula, which was presumably once the system that was searched for.
Rogue Planet None found/reported yet.
Stellar Remnant Nebula None found/reported yet.

Binary and multiple stars

Binary Star

Binary Star in Hegua WY-I d9-7 AB 3

Some star systems consist of two or more stars that orbit one or more common barycentres. These are typically referred to as binary star systems in the case of two stars, or multiple star systems in the case of more than two stars. For each star, the others in its system are known as companion stars. The first person who discovered binary stars was German-British astronomer William Herschel. He published the first catalogue of binary stars with measurements of their relative positions to the Royal Society in London in 1782 CE (269 double or multiple systems).[7] A second catalogue was published in 1784 (434 systems) and a third catalogue in 1821 (145 systems).[8] William noted that Newton's laws of gravity also apply outside of the Sol system. His son John Herschel found thousands more binary stars and updated the catalogue.[9]

Binary and multiple star systems are somewhat uncommon in the Milky Way galaxy, but they can present a travel hazard to unprepared pilots as they drop into a new system from hyperspace, as the distance between these stars can sometimes be only a few light seconds. A ship flying between an especially close pair of stars can easily overheat, which can be disastrous for explorers who happen to be thousands of light years away from a station.

Systems with binary or multiple neutron stars are especially rare. The system Dryuae Scraa BA-A g18, near Colonia, is the only known example of a system with two pairs of binary neutron stars.[10]

Ringed Stars

On rare occasions, stellar objects can host ring systems. This is much more common for Class T and Y brown dwarfs orbiting class B or O stars. Occasionally, Class L brown dwarfs will also host ring systems under similar circumstances. It is very rare for main-sequence stars to host ring systems, and this generally only occurs for Class M red dwarfs. White dwarfs and neutron stars may also have rings, with a similar level of rarity as M classes having rings.

Largest Stars

Comparison of planets and stars

Some of the largest and most well-known stars in the galaxy are listed below, from smallest to largest. They are ordered by solar radius which is the unit of measurement based on the radius of the sun in Sol (695,700 km; 432,288 mi).

The largest known star within 10k ly from Sol is Eta Carinae, located 7500 ly from Sol. The larger of the two stars weighs in at ~90 solar masses. It has a companion at ~30 solar masses (estimates are variable) and they are 750 ls apart at periastron.

UY Scuti and NML Cygni are not included because back in 2013 when the game's galaxy was being crafted, the diameter of UY Scuti had not yet been measured and reported in the popular astronomy press. At that time, VY Canis Majoris was "the largest star in the known galaxy".

Videos

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Rarity in relation to all stars (34 million in total), according to [1] on 10 Aug 2019. The usual disclaimers about bias(es) apply.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Based on the following thresholds: <1% Very Rare; 1-5% Rare, 5-10% Uncommon; 10-30% Common; >30% Very Common
  3. 3.0 3.1 3.2 3.3 Images marked with * were made an provided by schlowi123.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Classes according to the official Journal documentation (v25 for ED 3.4). Not all classes listed in the documentation are available/found within the game as per ED 3.4. The following undocumented classes have been found: B_BlueWhiteSuperGiant, G_WhiteSuperGiant
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Rarity in relation to entries within the table, according to [2] on 10 Aug 2019. The usual disclaimers about bias(es) apply.
  6. http://www.handprint.com/ASTRO/specclass.html
  7. Herschel, W. (1 January 1785). "Catalogue of Double Stars. By William Herschel, Esq. F. R. S". Philosophical Transactions of the Royal Society of London. 75: 40–126. doi:10.1098/rstl.1785.0006. Retrieved 5 June2018. Read December 8, 1784
  8. MacEvoy, Bruce. "The William Herschel Double Star Catalogs Restored". Astronomical Files from Black Oak Observatory. Retrieved 5 June 2018.
  9. Buttmann, Gunther 1974. In the shadow of the telescope: a biography of John Herschel. Lutterworth, Guilford. p50 & 197
  10. r/EliteDangerous: After Searching thousands of systems,finally found binary sets of neutron stars!
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