Talk:R136a1/Archive 1

Archive 1

Dark Matter

Would it so far out of the left field to surmise there maybe concentration of dark matter at the star's core ("stark" matter) to allow it to become so bulky? — Preceding unsigned comment added by 203.77.53.185 (talk) 14:29, 18 July 2011 (UTC)

@203.77.53.185

No.hi (talk)

Volume

Would this also be the largest star by volume (which seems to be closer to what the image shows anyway)? --Sfnhltb (talk) 14:12, 27 July 2010 (UTC)

Apparently not, see VY Canis Majoris. — Martin (MSGJ · talk) 14:43, 27 July 2010 (UTC)

@Sfnhltb

The image doesn't show R136a1 as a large star. It doesn't even look big.

Physical characteristics

Stars between about 8 and 150 solar masses explode at the end of their lives as supernovae, leaving behind neutron stars or black holes. Having established the existence of stars between 150 and 300 solar masses, astronomers suspect that such an enormous star will perish as a hypernova, a stellar explosion with an energy of over 100 supernovae (1046 joules).

wrong, make that 12 to 60, hypernova would be any star exceeding that mass. as to black hole, smallest black hole discovered yet is 3.8 solar masses and it was created either by collision of two neutron stars, or by a very large star exceeding 30 solar masses. Therefore article needs bit of editing...

That sentence was taken out when I rewrote it. hi (talk) 20:06, 10 May 2015 (UTC)

Ultraviolet Star

Its energy temperature (Boltzmann's constant multiplied by its kelvin temperature) is about 4.57 eV, which falls in the near ultraviolet range. So while the star looks blue to the human eye, and is described as blue in the text, it seems like it might be more accurate to refer to it as an ultraviolet star? Stonemason89 (talk) 19:12, 27 July 2010 (UTC)

It is not described as blue in the text, it is described as a blue hypergiant, which means it should be spectral type-O or type-B and luminosity class-0. "blue hypergiant" is a technical term indicating spectral type and luminosity class. 76.66.193.119 (talk) 07:19, 7 August 2010 (UTC)

I suppose it would be a good idea to create a section on the radiation profile of the star (what colour it looks like to the naked eye, the power spectrum of its radiation, etc) 76.66.193.119 (talk) 07:22, 7 August 2010 (UTC)

@Stonemason89@76.66.193.119

Done.hi (talk) 20:06, 10 May 2015 (UTC)

This star is of magnitude 12 and is seen with an amateur telescope.Was it too nebulous?

-Alexrybak (talk) 05:26, 31 May 2011 (UTC)

cleaning up intro

"currently on record" and "holds the record" in the intro were redundant so I removed them. It was also a bit jarring to see language more suited to sports reporting in a science article. Bhny (talk) 01:02, 15 September 2011 (UTC)

Confusing and populist. Astronomical observations are always discussed as of the time they are made, not the time that the light left the star. It can be fun to speculate what may have "happened already" but ultimately pointless and unhelpful. Lithopsian (talk) 23:39, 20 May 2012 (UTC)

Old, old comments, but I see my reply here doesn't make a lot of sense. I was probably replying to the next section. Lithopsian (talk) 15:11, 9 April 2015 (UTC)

Verb tense

Wouldn't it be more accurate to say "As of 165,000 years ago, R136a1 was a blue..."? Chrisrus (talk) 06:08, 20 February 2012 (UTC)

@Chrisrus

No. In astronomy, except for extraordinary situations where viewpoints come into question, you refer to events as they are seen here. That is, SN1987a occurred in 1987, not in pre-history. R136a1 is a blue star. 01:35, 9 April 2015 (UTC)

Large undo of recent edits

I have just made a large undo. This repeats much the same thing done about a week ago. Clearly I didn't explain my reasons well enough then, so here goes:

• invalid gammar (eg. "It was only until 2010 that the star was recognized to be the most massive", meaning not until 2010). Don't correct grammar unless you have a good grasp of the language.
• removing citation-needed tags without citing the questionable content (eg. the Pistol star was estimated to be 15,000,000L_☉ and 150M_☉).
• Much of the Surroundings section was lifted word for word from the linked R136 and Tarantula nebula articles. This article is about the star R136a1.
• Incorrect description of the Eddington luminosity as it relates to massive stars and their formation. There is nothing to prevent stars far exceeding 150 M_☉ (witness R136a1 itself), but the process of their formation is expected to be disrupted before they become that massive.
• Incorrect description of the evolutionary state of WNh stars. They are (most likely) core-hydrogen burners, certainly not core Nitrogen burners.
• Possible confusion of ionising radiation and just "radiation". I assume. At any rate the statements are incorrect. For example one single star in the Trapezium cluster in Orion produces more than 1/50th of the energy produced by R136a1.
• Assumption that luminosity alone causes the high mass loss observed. This is incorrect, and mass loss depends on the opacity of the material in the outer layers of the star, and the surface gravity, with details depending on particular spectral line opacity. Stars much less luminous than R136a1 have higher mass loss rates.
• Incorrect (still, after I gave the correct value in my previous edit) calculation of the relationship between relative radius and relative volume. Volume varies as the *cube* of the radius. Hence statements about the density are also incorrect. If you don't understand it, don't put your own calculations into the article.
• Overly strong statements about the metallicity of R136a1. I have found no references measuring or calculating the metallicity of the star, only an assumption of a possible value for the purposes of modelling. Such a value should be described very carefully, if at all, and certainly not stated as fact.
• Statement that R136a1 will continue to evolve along the W-R sequence is unsupported by the citations given. WNh stars such as R136a1 do not form part of the classical "WR sequence". They are young, even described as "main sequence" in the cited journal on account of still burning hydrogen in their cores. They evolve into supergiants, possibly blue hypergiants or LBVs, before (possibly) returning to the more typical hydrogen-free WR sequence, although the details are highly uncertain.
• Unsupported own research that x-ray output is large compared to visual light because of high temperature. In fact thermal x-rays are insignificant from any Wolf Rayet star. WN stars do produce some soft x-rays, exact origin unknown, but not measurable thermal x-rays. That requires temperatures of the order of a million Kelvin. The cited reference *specifically* describes this issue.

That may be enough for now. Possibly I removed one or two constructive edits and I apologise. I simply couldn't face making all the exact same line-by-line edits that I made a week ago in the hope of preserving an occasional gem. Lithopsian (talk) 16:06, 9 April 2015 (UTC)

@Lithopsian

@SkyFlubbler

I apologise for this. Maybe I was a bit to eager to expand the article so I didn't look into the details. Looking into the article, I find that it is poorly constructed, so perhaps you and me could expand this article and improve the content as you did with these edits to Eta carinae ([1] [2]). We should try to improve this article because this is a chief discovery in astrophysics. UY Scuti is important as R136a1 in astronomy, yet the article is well-written. Perhaps it is a matter of references, (UY Scuti's ref's mentions all of its properties) but we could try to pierce whatever we've got into a good article. We could also get SkyFlubbler into this because he is a good writer. (and when you reply, please leave it at my talk page) I am. furhan. (talk) 19:33, 9 April 2015 (UTC)i am. furhan.

@Lithopsian

The eddington limit section says, " In practice the theoretical Eddington Limit must be modified for high luminosity stars and the empirical Humphreys Davidson Limit is derived" That says that the eddington limit must be modified for high luminosity stars, i.e R136a1.

@Lithopsian

Distance

The distance to the Magellanic Clouds is widely accepted to be 50kpc (49.97kpc as now described in the article), but I'm intrigued by the description just added of a specific distance to R136 of 48.2kpc. The reference given (poorly formatted, no title, just an eprint url) does not seem to contain anything about eclipsing variable distances to R136. Wrong paper? Lithopsian (talk) 13:00, 5 May 2015 (UTC)

Comment

@Lithopsian Just wanted to ask a question here. I find that Eta Carinae, at 5 million L_☉ and 120 M_☉, is around 2.133 times less massive than R136a1, at 256 M_☉ and 7.4 million L_☉. R136a1 is only 2.4 million times more luminous than Eta Carinae, or 1.48 times. So I was just wondering; shouldn't R136a1's luminosity be far more greater than η Car's?. I mean, a 2.13 solar mass star (Vega, as an example) is around 40× more luminous than the sun. If this was the case with R136a1, it would be around 300,000,000 L_☉. So my question is; shouldn't R136a1's luminosity be far more greater? Or does Eta Carinae (and other stars) have a higher rate of core energy generation? If this is the case, than why isn't it for Vega? I know that I am wrong somewhere, but can someone please explain? If this is a case of evolution, than will R136a1 increase in luminosity as it evolves? hi (talk) 22:04, 6 May 2015 (UTC)

Apples and oranges. Mira has almost the same mass as the sun, yet is 10,000 times more luminous. Lithopsian (talk) 22:11, 6 May 2015 (UTC)

It might have something to do with the fact that Eta Carinae is 10 times larger than R136a1. exoplanetaryscience (talk) 22:14, 6 May 2015 (UTC)

Not really. Mira is much bigger than R136a1, but less luminous. The same luminosity can potentially be expressed by stars of different sizes and temperatures, but ultimately that energy comes from fusion inside the star. Lithopsian (talk) 19:54, 8 May 2015 (UTC)

@Lithopsian

So it is due to the fact that Eta Carinae is more evolved than R136a1? hi (talk) 23:00, 6 May 2015 (UTC)

Better phrased, as a different stage of stellar evolution.See the Hertzprung Russell diagram and discussions about how stars move on that diagram in time. At different stages in a star's lifetime, it will show drastically different luminosities. There isn't a direct relationship between mass and luminosity, except for stars at similar phases in their lifespans. E.g. Lifespan

Tarl.Neustaedter (talk) 19:05, 8 May 2015 (UTC)

Physical proprieties of R136a1

In a VLT flames survey paper, the authors said,

"In our present work we tried to follow a well-defined method of analysis as described in Sects. 3.2, 3.3 and 3.4. In this section we present comparisons with previous works to get a better pic- ture of the systematic uncertainties that can arise from different analysis methods. A comprehensive study of WR stars in the LMC has recently been published by Hainich et al. (2014), who have analysed 17 stars from our present sample. These authors used a simi- lar grid approach as in our work, based on the Potsdam Wolf- Rayet (PoWR) model atmosphere code (Koesterke et al. 2002; Gräfener et al. 2002; Hamann & Gräfener 2003). An important difference with respect to our work is how the stellar luminosi- ties and interstellar extinction are determined. As described in Sect. 3.4 our results mainly rely on IR Ks-band photometry. The optical flux in B and V is matched simultaneously with the IR by adapting RV and E(B − V) in the extinction law. Hainich et al. keep RV fixed and mainly use the optical to UV flux to de- termine E(B − V) based on the LMC extinction law by Howarth (1983). As discussed in Sect. 3.4 this approach may lead to sub- stantial errors if RV deviates from the adopted value. The anal- ysis of Hainich et al. largely relies on the UV range where the uncertainties in the extinction are very high. Our results rely on the IR where the extinction is almost negligible, however, there is a danger of contamination by circumstellar dust or other IR sources. An illustrative case is VFTS482 (BAT99-99, Mk39). For this star Hainich et al. obtain a luminosity of log(L/L⊙) = 5.9 while our value lies significantly higher (log(L/L⊙) = 6.4). As described above Hainich et al. do indeed substantially underes- timate the IR flux for this object. However, there is possible ev- idence for crowding in HST images of this star (cf. Table B.1). Could the excess IR flux thus be due to other sources? Our SIN- FONI IR data of VFTS 482 suggests that this is not the case as the IR spectrum shows the correct line strength, i.e., it is un- likely that the IR is contaminated by other sources. The same holds for the optical range for which a comparison between HST and UVES spectroscopy shows no sign of contamination. For VFTS 482 we are thus confident that our approach is correct. Furthermore, the different wavelength coverage and larger S/N ratio of the VFTS data can explain discrepancies arising from differences in the line diagnostics. This partly leads to different He-abundances (VFTS 482 and 545) and temperatures (∆T 􏰄 10 000K, e.g. for VFTS 545, 617, 1017, and 1025). Af- ter correcting for clumping, there is also a systematic offset of 0.1 to 0.2 dex in the mass-loss rates noticeable. This difference lies within our error bars and is most likely caused by different assumptions in the model physics and atomic data."

This might imply that the stellar parameters derived by hainich et al. are not as reliable as the ones derived by crowther et al. So maybe we could put the numbers back. 142.177.125.164 (talk) 19:01, 10 May 2015 (UTC)

Crowther says Crowther's figures are more reliable than Hainich's? I don't think that's going to make the front page of many newspapers. Is it better to take accurate IR figures and extrapolate wildly to cover that 98% of the radiation that occurs in the UV, or take less accurate UV measurements and not have to extrapolate so wildly? How long is a piece of string! My personal opinion, probably, don't quote me on this, is that the 2010 Crowther paper might be more "accurate", but it is important to remember that none of these numbers can realistically be considered better than ballpark estimates, considering all the sources of errors outside the small model differences they're arguing about. That isn't really for me to decide, luckily. I simply try to pick the most recent paper that isn't obviously speculative or out in left field and preferably takes note of previous publications. In this case it is the Hainich paper, which has the advantage of providing a self-consistent set of values for all the LMC WR stars, but certainly with some caveats that even Hainich acknowledges. Don't fall into the trap of wanting to use a particular number and looking for reasons why you can. You can always discuss differences between different authors in the text. Even perhaps put a range of values in the starbox although I try to avoid doing that except as a last resort - too confusing, could be mistaken for actual variability, etc. Lithopsian (talk) 20:21, 11 May 2015 (UTC)

@Lithopsian You did the same thing with Pistol star here. Hainich does't say that crowther's figures are more reliable, but he does acknowledge that the perimeters derived are uncertain so maybe crowther's are more reliable.aaaaaaaaaaaaaaaaaaaaaa (talk) 00:33, 28 May 2015 (UTC)

I "did the same thing"? You mean I changed a data value from one you liked (ie. a big number for a star you feel an affinity for) to one that is likely to be the best available in the literature? Normally I would suggest that you use experience and a thorough understanding of the published sources to try and extract the most reliable number (if you must extract only one), but I fear you'd just use that as an excuse to cherry-pick your favourite numbers. That is absolutely *not* the right approach. It doesn't matter that every schoolboy for the last decade has been brought up thinking VY Canis Majoris is the biggest star and R136a1 is the most massive and luminous. If new research gives a different answer, then Wikipedia should change. Then all those schoolboys, now young men full of testosterone and their own sense of omniscience, will come along and try to change the article to match what they thought was god-given fact. C'est la vie, try to rise above.

The VLT-FLAMES census is a good recent source for many of these stars. More than just WR stars in the Tarantula region, but not full coverage of the LMC. If nothing else, it is a valuable cross-reference against Hainich's values. Certainly try to consider both sources when a star is included in both. Perhaps more importantly, read Hainich's comments instead of just blindly yanking out numbers. If he says a value is dubious then perhaps ignore it, for example the BAT99-98 which isn't explicitly considered "wrong" as many of the known binaries are but is certainly described as highly uncertain. Lithopsian (talk) 12:15, 28 May 2015 (UTC)

Worklist

@Lithopsian@Casliber@StringTheory11@Huntster Hi guys, I know from some comments here that this article needs a lot of work. I've been trying to expand it over the past few weeks but can someone maybe help out? Also, this article needs a worklist which I can probably not compose. I know the visibility and future sections could use some work and the size, temperature, mass, and mass loss could use a little expansion (and maybe luminosity, since there are a couple of things that I could add). Now, I just mentioned the basics here but I need someone else to compose a more comprehensive one.aaaaaaaaaaaaaaaaaaaaaa (talk) 19:05, 7 June 2015 (UTC)