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Wolf-Rayet Star
 Image from Trolligi | |
| WR 142, a Wolf-Rayet star 5,382 ly from Sol | |
Characteristics
Wolf-Rayet stars represent an evolutionary phase in the lives of massive stars during which they undergo heavy mass loss. They are characterized by a spectrum dominated by emission lines of highly ionized elements. These extremely hot (up to ~260,000 K) and very luminous (5E+4 to 1E+7 solar luminosities, with an average of 3E+5) stars are very rare, reflecting the short timescales of the Wolf-Rayet stage - only around 30 of these stars are currently in the Terragen Sphere. Intense stellar winds drive mass loss rates of between 1E-6 and 1E-4 solar masses per year; the latter are many times greater than expected for other hot, O-type or B-type stars, the former of which are the predecessors to these stars.There are three main types of Wolf-Rayet stars - carbon-rich (WC), nitrogen-rich (WN), and hydrogen-rich (WNh, also rich in nitrogen), the latter two of which are more common, especially in low-metallicity galaxies. The evolution of the star in its Wolf-Rayet stage is dependent on its initial mass. On their own, lower-mass WRs are unable to evolve into the WC class (and so are confined to the WNh class and then the WN class) as they don't have powerful enough stellar wind to eject enough mass to expose the carbon and oxygen fusing in their cores, although binary stripping - where a more massive companion strips the outer layers of the WN star - can reveal the latter's carbon-rich interior and making it a WC star. This is also how some very low mass stars can become small WN stars. More massive stars, on the other hand, can naturally attain the WC class through a lot of mass loss and proceed to get hotter and hotter, finally transitioning to the WO stage (the oxygen-rich stage) where they become extremely hot (over 130,000 K), and after under twenty thousand years, explode as type Ic supernovae.
The composition of WR stars can be quite extraordinary. WNh stars are not too different from regular stars, with a significant percentage of nitrogen. This amount increases as the WNh star loses mass very rapidly (WNh stars are especially prone to extremely strong mass loss, on the order of 1 solar mass every 10,000 years), expelling all of hydrogen and becoming a hydrogen-free WN star.
WN stars are made almost entirely out of helium with ~1% (a sizable amount) of it being made of nitrogen. Then, mass loss carries even more material away and then starts to expose the inner layers of the star. The WN star briefly becomes a WN/WC star, also called a transitional Wolf-Rayet star, another rare subtype of WR. Carbon level rises during this period.
After the star becomes a WC star, the level of helium substantially decreases to only half of the star's mass. The other half is carbon with a small amount of oxygen making up some 1-10% of the star. As the WC star shrinks and heats up, helium level decreases further, while carbon and oxygen levels increase. As the star transitions from WC to WO, helium now makes up between 30 and 10% of the star, while oxygen comprises about 20% of the star, and the rest is taken up by carbon. There is also a significant amount of iron in the star (~0.1%).
Finally, the WO star explodes and scatters all these elements across space.
Utilisation of Wolf-Rayet stars within the Terragen Sphere
Due to their high masses, WR stars are often utilized by archailect-level entities. Most WR stars are in the process of being disassembled by starlifting, the extracted mass either used to build computation nodes or other types of mass-intensive constructions. Since WC stars produce a lot of dust, it is possible to mine this dust and obtain a lot of carbon and oxygen as an alternative, slower resource extraction method.As Wolf-Rayet stars are extremely rare and mostly limited to young star clusters, they do not generally pose a great threat except to nearby systems. WRs are extremely bright and emit a fair bit of high energy radiation such as UV and X-rays. Therefore, colonizing systems located very close to Wolf-Rayet stars generally require radiation-resistant modifications, such as those utilised by the Radiation Nation and similar tweaks.
Wolf-Rayet stars can become tourist sites because of reasons such as their rarity, and the surrounding nebulosity, which many WRs possess. A lot of precaution is often taken when travelling there for touristic purposes, and for a good reason.
List of Wolf-Rayet Stars within the Terragen Sphere
About half of these stars have been colonised by non-Sephirotic metaempires, particularly the Solipsist Panvirtuality, so information about these systems is limited.| Name | Spectral type on discovery | Distance from Sol (light years) | Constellation | Notes |
| Gamma2 Velorum A / WR 11 | WC8 | 1100 | Vela | First WR star to be stabilised |
| WR 94 | WN5o | 3100 | Scorpius | stabilised |
| WR 146 A | WC6 | 3590 | Cygnus | stabilised (by Solipsist Panvirtuality) |
| WR 90 | WC7 | 3750 | Scorpius | stabilised |
| WR 78 | WN7h | 4080 | Scorpius | stabilised |
| WR 139 A | WN5o | 4270 | Cygnus | stabilised (by SP) |
| WR 79 A | WC7 | 4470 | Scorpius | stabilised |
| WR 145 | WN7o/CE | 4670 | Cygnus | stabilised (by SP) |
| WR 120 | WN7o | 4890 | Scutum | stabilisation commenced |
| WR 110 | WN5-6b | 5150 | Sagittarius | stabilised |
| WR 111 (Muora) | WC5 | 5320 | Sagittarius | This star exploded in 8684 AT, after Terragen explorers arrived |
| WR 140 A | WC7 | 5350 | Cygnus | stabilisation commenced (by SP) |
| WR 142 | WO2 | 5380 | Cygnus | This star exploded as a Gamma-Ray Burst in 2055 AT, luckily missing the Terragen Sphere completely |
| WR 105 | WN9h | 5640 | Sagittarius | stabilisation commenced |
| WR 52 | WC4 | 5710 | Centaurus | Went supernova |
| WR 134 | WN6b | 5710 | Cygnus | stabilisation commenced (by SP) |
| WR 144 | WC4 | 5710 | Cygnus | Went supernova |
| WR 93 A | WC7 | 5740 | Scorpius | |
| WR 142-1 | WN6o | 5770 | Cygnus | |
| WR 147 A | WN8(h) | 5840 | Cygnus | |
| WR 113 A | WC8 | 5870 | Serpens | |
| WR 142a | WC8 | 5900 | Cygnus | |
| WR 159 | WN4 | 5940 | Cassiopeia | |
| WR 133 A | WN5o | 6030 | Cygnus | |
| WR 113-2 | WC5-6 | 6070 | Scutum | |
| WR 141 A | WN5o | 6290 | Cygnus | |
| WR 136 | WN6b(h) | 6290 | Cygnus | |
| WR 70-5 | WC9 | 6360 | Norma | |
| WR 98 | WN8o/C7 | 6390 | Scorpius | |
| WR 25 A | O2.5If*/WN6 | 6430 | Carina | |
| WR 135 | WC8 | 6460 | Cygnus | |
| WR 85 | WN6h | 6490 | Scorpius |
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Development Notes
Text by Trolligi
Additional material by The Astronomer
Initially published on 24 July 2021.
Additional material by The Astronomer
Initially published on 24 July 2021.
