Talk:List of largest known stars

Lower UY Scuti again?

Last time I checked, UY Scuti has a size of 825 SR on here. When was it moved back up to 1708? I heard it was unreliable. Should we lower it back down again? Atlantlc27Lol (talk) 19:16, 7 November 2023 (UTC)

I was thinking of removing it, NML Cyg and some other stars that have effective temperatures substantially lower than the Hayashi line, which could indicate that they are not in hydrostatic equilibrium which would be very unusual if it was permanent. UY Sct has a radius that uses an old distance anyway and a noiseless photogeometric distance based on Gaia EDR3 data, which is also less uncertain and results in a radius of 1,060+118
−98 R_☉ although that would not be added to the list since it fails WP:SYNTHESIS. Wing (2009)'s "Biggest Stars of All" also states that it would be hard to believe that a star like NML Cyg could be stuck in a non-equilibrium state for more than 40 years. Dorn-Wallenstein et al. (2023) states that the Hayashi line is 3650 K, however it also mentions two papers that put the limit at 3450 K for the Large Magellanic Cloud, which is more consistent with stars like WOH G64. Wing (2009) states the Hayashi line to be at around 3550 K, which is also consistent with good observations. SpaceImplorerExplorerImplorer 19:49, 7 November 2023 (UTC)

Well the temperaature of IRC -10414 (3110 - 3300 K) is also below the Hayashi limit and it's a M7 RSG too (NML Cygni is a M6I star). Diamantinasaurus (talk) 20:21, 7 November 2023 (UTC)

NML Cyg’s effective temperature of 3250 K is a direct assumption from its spectral type, where the measured T_eff comes from a source in 1980 that purely uses old interferometry and fluxes for some giant stars. The effective temperature used in the 2012 paper is extremely uncertain anyway and the luminosity leads to a really uncertain radius, and, again, Wing (2009)’s “The Biggest Stars of All” mentions that it would be hard to believe that NML Cyg could remain in non-equilibrium for over 40 years. SpaceImplorerExplorerImplorer 07:21, 8 November 2023 (UTC)

Such a low effective temperature would actually be unlikely or at least very unusual, since the mass-loss rate would be much higher than what is observed. (see Gvaramadze et al. (2014) on page 11) An effective temperature of 3700 K was estimated in Levesque et al. (2005), which is more consistent with the observed mass-loss, however it is inconsistent with its spectral type. SpaceImplorerExplorerImplorer 07:38, 8 November 2023 (UTC)

An important thing to note is that the radius estimate (1,708) is partly circular. The distance comes from a very old source which assumes a distance based on an assumed absolute magnitude based solely on the luminosity class. The newer paper then re-determines a luminosity based on that distance, rather than using the original value. The other stars with angular diameter estimates have estimated distances from much more direct and accurate methods like masers and association membership, so they should be kept, but UY Scuti should likely not be. VY Canis Majoris (talk) 20:32, 7 November 2023 (UTC)

The 1970 paper estimates that the distance to RW Cep is 1.8 kpc, where in reality it is around 3.4 kpc Diamantinasaurus (talk) 20:36, 7 November 2023 (UTC)

no we cant remove uy scuti from being the biggest can you add it? 2601:2C6:580:EEB0:7C30:9C59:994:7CD6 (talk) 23:21, 27 January 2024 (UTC)

Just because you don’t like it being off the list doesn’t mean it should be added back. SpaceImplorerExplorerImplorer 09:50, 28 January 2024 (UTC)

you don't want it being off the list doesn't mean it should be re-added. uy scuti is back on the list recently but with a lower radius based on effective temperature,... Hoanghao314159 (talk) 12:42, 15 April 2024 (UTC)

This should be archived, its back on the list with a better radius. Atlantlc27Lol (talk) 01:36, 2 May 2024 (UTC)

Removal of HV 888

HV 888 was said to be among the largest known stars, but it’s radius estimate varies too much, from 762 to 1,765 solar radii.

This indicates very poor certainty, making its values unreliable.

As a result, it had to be removed from the list.

Stars with smaller variations and better certainty can qualify as members. Eric Nelson27 (talk) 09:18, 3 December 2023 (UTC)

It is still useful to take into account the reliability of each estimate. Massey et al. (2022) got to a very plausible effective temperature of 3650 K and a log(L) of 5.48. The lower and higher values you mentioned have problems with accuracy; the lower value is derived from very low resolution spectra, that even got to a very low distance and the higher value is in a catalogue that contains all sorts of overestimated radii, which is typical if it contains more extreme stars like HV 888. SpaceImplorerExplorerImplorer 11:47, 3 December 2023 (UTC)

Well some stars have been removed by various users due to too much uncertainty in their radii.

NML Cygni, UY Scuti, and Stephenson 2-18 are great examples. Eric Nelson27 (talk) 01:23, 4 December 2023 (UTC)

The difference with them is that they don’t have any reliable radii. SpaceImplorerExplorerImplorer 07:09, 4 December 2023 (UTC)

UY Scuti and Stephenson 2 DFK 1 have no accurate distance estimates (UY Scuti's 2.9 kpc distance estimate is outdated and Gaia parallaxes have very high levels of astrometric noise, the Gaia parallax of RSGC2-01 is literally negative and it's not a member of the cluster in its name). NML Cygni's radius is based on an estimated temperature which is too cold and the star is probably smaller anyway (but it's still very big). The HV 888 smaller estimate is unreliable. If we are counting that, then WOH G64 should be removed too because it's radius estimate range from 1,540 R_☉ to 13,127 R_☉ (which is from the same paper as 1,765 R_☉ HV 888 by the way). Diamantinasaurus (talk) 14:12, 4 December 2023 (UTC)

1800 pc is noiseless unlike the actual Gaia data release parallax. WOH G64's estimate has however been carefully constrained for inaccuracies, making it currently a likely candidate for the largest known star. 13,108 R_☉ is in a large-scale survey that has many overestimations. SpaceImplorerExplorerImplorer 14:35, 4 December 2023 (UTC)

The size estimate of WOH G64 is indeed accurate. HV 888 is also very large and the size estimate is probably accurate. Diamantinasaurus (talk) 15:12, 4 December 2023 (UTC)

I calculated a size of 1,514 Rs for HV 888 but redid it and got 1374 Rs. I used a luminosity of Reid, from 1990 for the first one, and then the values stated. Cosmicwolfanimations (talk) 00:59, 3 March 2024 (UTC)

Technically, you could also say it varies from 762-1974 solar radii, because the 1974 solar radii estimate was on the list for a while (at least it was in 2020 & 2021) Atlantlc27Lol (talk) 03:28, 25 December 2023 (UTC)

1974 solar radii is not a good estimation. SpaceImplorerExplorerImplorer 10:44, 25 December 2023 (UTC)

1,765 probably isn’t either Atlantlc27Lol (talk) 17:34, 27 December 2023 (UTC)

V354 Cephei

The size of 1,520 solar radii for V354 Cephei was removed without reason known to me. Should we re-add it? It would also make it the largest known star in the Milky Way, and the second (or third counting MSX LMC 839 which was also removed without reason known to me), only 20 solar radii behind WOH G64. Atlantlc27Lol (talk) 23:59, 14 December 2023 (UTC)

1,520 R_☉ uses a very high extinction value and is therefore unlikely to be accurate. The star is still on the list but with a lower radius. SpaceImplorerExplorerImplorer 07:46, 15 December 2023 (UTC)

What about MSX LMC 839? Atlantlc27Lol (talk) 11:37, 15 December 2023 (UTC)

It is on here, however, it is named TRM 89 which is another designation for the star. SpaceImplorerExplorerImplorer 13:06, 15 December 2023 (UTC)

The reason for the removal is because V354 Cephei is only 3.6-3.7 solar masses, far less than most red supergiant stars. Hoanghao314159 (talk) 09:17, 10 February 2024 (UTC)

That’s based on Gaia data SpaceImplorerExplorerImplorer 09:25, 10 February 2024 (UTC)

Remove all the stars in galaxies other than Milky Way and the Magellanic clouds?

The stars in galaxies other than Milky Way and the Magellanic clouds should be removed simply because their sizes and other characteristics are very inaccurate (they are too far from Earth to be measured accurately). The star "Godzilla" (in Sunburst galaxy) broke the variability rule (470-2365 solar radii) and its luminosity is too high while its temperature is equivalent to a B6-O9 type star. The largest transient events' sizes are somewhat equivalent to the Quasi star's size (10000-30000 solar radii) and they are very likely to be old and inaccurate radii. The supernova progenitors are mostly too big to be real stars (since we removed UY Scuti). Hoanghao314159 (talk) 13:05, 12 January 2024 (UTC)

There is no clear reason for the stars beyond the Magellanic Clouds to have inaccurate sizes. "Godzilla" has radii that should be correct for specific modelled effective temperatures. It and other stars undergoing or that undergone outbursts, which are transient events, usually increase their size by a huge margin. The sizes on the list for supernova progenitors are mostly accurate and are 'breakout' radii, rather than their usual ones before the supernova. SpaceImplorerExplorerImplorer 18:42, 12 January 2024 (UTC)

Inaccurate radii simply because of larger distances Hoanghao314159 (talk) 09:09, 10 February 2024 (UTC)

Larger distances doesn’t exactly mean that it has to be inaccurate. SpaceImplorerExplorerImplorer 09:15, 10 February 2024 (UTC)