Talk:Black hole

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Semi-protected edit request on 10 December 2019

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After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses (M☉) may form.

to

Another category of these objects are supermassive black holes of millions of solar masses (M☉).

COMMENT: PLEASE ASK ANY ASTROPHYSICIST (I AM THE ONE FROM POLAND) - SUPERMASSIVE BLACK HOLES DO NOT FORM FROM THE ONES OF SOLAR MASSES, ESPECIALLY IN THE MODERN UNIVERSE - THEY HAVE FORMED BILLIONS YEARS AGO, NOW "STELLAR" BLACK HOLES LIVE USUALLY QUIETLY FOR BILLIONS OF YEARS TO COME, NO CHANCE TO FORM NEW SUPERMASSIVE BLACK HOLE. THANK YOU FOR THE CHANGE IN ADVANCE! 77.245.247.62 (talk) 08:22, 10 December 2019 (UTC)

 Not done: please provide reliable sources that support the change you want to be made. Unfortunately asking an astrophysicist is not a sufficient source. We need to use a reliable, published source. ‑‑ElHef (Meep?) 16:00, 10 December 2019 (UTC)

File:Black hole - Messier 87 crop max res.jpg to appear as POTD soon

Hello! This is a note to let the editors of this article know that File:Black hole - Messier 87 crop max res.jpg will be appearing as picture of the day on December 21, 2019. You can view and edit the POTD blurb at Template:POTD/2019-12-21. If this article needs any attention or maintenance, it would be preferable if that could be done before its appearance on the Main Page so Wikipedia doesn't look bad. :) Thanks! Cwmhiraeth (talk) 11:01, 10 December 2019 (UTC)

Picture of the day

A black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing – no particles or even electromagnetic radiation such as light – can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed.

This picture is a photograph of the shadow of the supermassive black hole at the centre of the Messier 87 (M87) elliptical galaxy in the constellation Virgo, as captured on 11 April 2017 by the Event Horizon Telescope, a planet-scale array of eight ground-based radio telescopes, a collaborative effort by scientists from over 20 countries; the photograph itself was released on 10 April 2019. As a black hole is a completely dark object from which no light escapes, its shadow is the next best alternative to an image of the black hole itself. The event horizon, from which the telescope takes its name, is around 2.5 times smaller than the shadow it casts and measures just under 40 billion kilometres (25 billion miles) across.Photograph credit: Event Horizon Telescope

Suggestions to make this page more readable

The page should be rewritten with a general reader in mind. Pertinent questions would include: has anyone ever seen a black hole? If so, when was the first sighting made? As it currently stands, the page bogs down in endless details and jargon of theoretical models, without ever really making a persuasive argument that black holes do exist and are not just speculative constructs. -Wwallacee (talk) 11:47, 24 December 2019 (UTC)

There's an entire section of the article devoted to observational evidence of black holes. –Deacon Vorbis (carbon • videos) 12:39, 24 December 2019 (UTC)

And the lede includes a picture. XOR'easter (talk) 15:50, 24 December 2019 (UTC)

Rotating event horizon shape

The last sentence of the event horizon section says "For non-rotating (static) black holes the geometry of the event horizon is precisely spherical, while for rotating black holes the event horizon is oblate."

https://en.wikipedia.org/wiki/Kerr_metric#Important_surfaces provides equations for both the ergosphere and event horizons of a rotating black hole. The equation for the event horizon can only ever describe a perfect sphere (there are no theta or phi terms).

These two things are inconsistent. In my estimation, some people have confused the ergosphere for the event horizon and the second to last sentence of the event horizon section should drop the word "approximately" and the very last sentence should be entirely removed. — Preceding unsigned comment added by 199.116.184.9 (talk) 20:28, 9 January 2020 (UTC)

Done, more or less. The question remaining, which is over my head, is if it's worth discussing non-equilibrium stages during formation. WolfmanSF (talk) 00:15, 10 January 2020 (UTC)

I think this needs further discussion before any change should be made. As Misner, Thorne and Wheeler say, "in general, black holes are not spherical" (Gravitation, p. 899). IIRC, the apparent sphericity is an oversimplification based on a coordinate artifact; see Smarr (1973), the discussion around Eq. (116) of Visser (2007), and Delgado, Herdeiro and Radu (2018). XOR'easter (talk) 00:19, 10 January 2020 (UTC)

Okay, for your sources could you please check the context to confirm that they are specifically discussing the event horizon? Also, (if they are correct) we should change the Kerr_metric and Kerr–Newman_metric pages to use the correct (non-spherical equations) or explain how/that the equations are only approximations.199.116.184.9 (talk) 21:31, 10 January 2020 (UTC)

I double-checked each one to make sure they were taking about the event horizon and not the ergosphere. I agree that the Kerr metric and Kerr–Newman metric pages could stand revision; as best as I can tell, the issue isn't one of approximation per se, but one of translating results from a coordinate system where it is easy to derive results to something that matches what we mean when we say "the shape of the black hole" in everyday language. XOR'easter (talk) 21:51, 10 January 2020 (UTC)

Given that the ref. currently in use for oblateness mainly describes a temporary toroidal geometry that may arise during collapse, I think we might start by replacing that source with the three more relevant ones you have provided. WolfmanSF (talk) 08:38, 12 January 2020 (UTC)

Energy loss, escaping or gaining "negative deposits", and another development suggestion.

@TimothyRias I argued against denying absolutely escape from inside event horizon, for a couple of reasons.

In Stephen Hawking's words, "gravitational collapse produces apparent horizons but no event horizons" and "The absence of event horizons mean that there are no black holes - in the sense of regimes from which light can't escape to infinity." So Hawking has arrived at the conclusion that even ligth could escape, and denied event horizons totally.

The negative energy deposit you mentioned is apparently connected only with Hawking radiation. I do not buy the idea without confirmation that particles (the deposits) having negative mass do exist. Has somebody confirmed the existence of such particle? If not, energy of radiation originates from BH likely transmitted by timespace. It has after all been confirmed that timespace can transmit energy, and information, carried by gravitational waves, and as I know, it has not been confirmed that EH would stop GWs.

I assume, that during the merger ans ringdown phases of binary BH merger, while the matter of both BH's are inside the joint event horizon but the final stable sphere is not formed yet, gravitational waves are still generated and carrying energy out from inside EH.

For this reasons, the phrase "acceleration so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it" is too strict and also commonly seen doubfull. In a fact, GR does not anyway deny energy escape carried by GWs, so the phrase must be missinterpretation.

According to the fundamental gravitational collapse models, an event horizon forms before the singularity of black hole. Thus EH really can exist without BH. It has been calculated that if all the stars in the Milky Way would gradually aggregate towards the galactic center while keeping their proportionate distances from each other, they will all fall within their joint Schwarzschild radius long before they are forced to collide. Up to the collapse in far future, observers in a galaxy surrounded by an event horizon would proceed with their lives normally.

On the other hand, an apparent horizon always implies the existence of BH whereas EH does not, therefore an apparent horizon should be named as defining feature of a black hole, not EH. Yoxxa (talk) 14:02, 28 March 2020 (UTC)

Please provide a strong source that explicitly states that, for example, "gravitational waves are still generated and carrying energy out from inside EH"; if there is no such strong source, we'll have to wait for mainstream science to catch up with you before we can add this to Wikipedia. Rolf H Nelson (talk) 00:28, 29 March 2020 (UTC)

This should be self-evident. According to GR binary black hole mergers always emit energy as gravitational waves, regardless if they have separate or joint event horizons. EHs are only calculated theoretical distances where paths of light are turning inwards, they have no affect to spacetime's form or it's possible changes or vibrations. I'll keep my eyes open if this detailed description would show up in some scientific paper. Yoxxa (talk) 16:34, 30 March 2020 (UTC)

In GR, gravitational waves also cannot escape an event horizon (and also cannot cross an apparent horizon).TR 14:51, 30 March 2020 (UTC)

Please provide a strong source that explicitly states that. Yoxxa (talk) 16:34, 30 March 2020 (UTC)

This will do [1] TR 17:52, 30 March 2020 (UTC)

Numerical BH merger models are skipping the question what is inside horizon, because that is not in the focus of their studies. As the document you referred tells: "Simulations of binary black hole systems using the Spectral Einstein Code (SpEC) are done on a computational domain that excises the regions inside the black holes." "Black hole excision is a means of avoiding the physical singularities that lurk inside black holes. The idea is to solve Einstein’s equations only in the region outside apparent horizons, cutting out the region inside the horizons."

In both separate and unified horizon cases, matters are losing part of their masses emitting it as gravitational waves, hence black holes actually do emit energy. That is my original point and reason for the correction to the page. Yoxxa (talk) 16:19, 31 March 2020 (UTC)

Do you have any sources to back up your claim? Talk pages are not a forum. - Parejkoj (talk) 16:57, 31 March 2020 (UTC)

Indeed WP:FORUM. Also try to understand why excision is a valid strategy.TR 18:28, 31 March 2020 (UTC)

Will this do? The radiation comes out either from inside separate or joint horizons or both, but it does, and joint mass-energy has decreased by out radiated energy. Can there just be any stronger source? Yoxxa (talk) 10:19, 1 April 2020 (UTC)

References

Won't do—see wp:CIRCULAR. - DVdm (talk) 12:34, 1 April 2020 (UTC)

Critical remarks on presentation of speculative topics

I think that an encyclopedia, online of otherwise, should mostly describe scientific findings, results and theories which are proven and widely accepted in the scientific community. Speculative scientific publications should not be featured; or if one thinks there is a point in doing so, perhaps because certain topics are trending in the scientific discussion, they should be clearly described as being speculative. I am referring here in particular to the presentation of topics regarding "firewalls" and "information loss". As far as I can see, the presentation of those highly speculative discussions is biased towards a particular point of view which so far ought to be regarded as controversial. The "firewall paradox" isn't generally accepted among physicists, see e.g. the article "Information Loss" by William G. Unruh und Robert M. Wald, published in: Rept.Prog.Phys. 80 (2017) 9, 092002; e-Print: 1703.02140 [hep-th]. At least it should be pointed out in a balanced encyclopedia entry that there is a controversy. Similarly, writing "According to widely accepted research by physicists like Don Page[197][198] and Leonard Susskind..." would be difficult to verify as to the statement "widely accepted". For my taste, this reads too much like a promotional piece towards a certain point of view among several on a highly speculative, unproven and experimentally unexplored part of the frontiers of physics. As pointed out initially, that is not the way of seriously writing about physics in an online encyclopedia. I hope you see the point, and will see yourselves in the position to make due amendments. Yours truefully, Magellanus. — Preceding unsigned comment added by 178.14.42.237 (talk) 22:28, 7 April 2020 (UTC)

The 'widely accepted' may stem from the Nature overview cited at the end of paragraph. What's widely accepted is not the existence of a firewall, but rather that the discovery of the "firewall paradox", that existing semiclassical physics was inconsistent. If there's a less confusing accepted name for the "firewall paradox", we can certainly use it. The Rept.Prog.Phys. doesn't seem to deny the paradox, but rather seems to state that the solution is to abandon unitarity. Feel free to submit an edit if you have a better idea how to phrase it. The section can certainly be trimmed if people think it's WP:UNDUE, but otherwise, if people don't want to read about "open problems" that are (by definition) unproven, they can just skip the section titled "open problems". Rolf H Nelson (talk) 04:47, 8 April 2020 (UTC)

Isn't the "firewall paradox" just another incarnation of the "information paradox"? Ultimately this paradox boils down to that you cannot simultaneously have unitarity, semi-classical quantum field theory at the horizon, and locality without creating some contradiction. The opinions on which to give up differ strongly depending on who you are talking to. The challenge for this page is to provide a neutral overview of these different views. This however is very difficult to do, because the many sources will strongly tend towards on of the solutions.TR 11:41, 8 April 2020 (UTC)

They are related, but logically distinct. Susskind's original black hole complementarity proposal satisfied the information paradox but not the firewall paradox. Rolf H Nelson (talk) 22:27, 11 April 2020 (UTC)

I should add that Unruh and Wald emphasize that "unitary", at least in the sense it is commonly used by the proponents of "firewall" ideas, is not as fundamental as it is often portrayed, and that in certain situations - such as those discussed in black hole evaporation - a breakdown of unitarity is not equivalent to leaving the framework of quantum mechanics (or quantum field theory) per se. Anyway, giving a balanced account of the discussion admittedly is difficult. I agree that very different opinions on that topic are held in various quarters of the theoretical physics community. I may think about it and propose a more neutral (from my perspective) formulation of the matter. However, for the time being, a fix could be to cite the paper by Unruh and Wald as the main source of prominent voices of a critical position towards firewalls, together with the comment that the issue isn't settled and subject to current research in theoretical physics. Yours truefully, Magellanus — Preceding unsigned comment added by 178.14.68.29 (talk) 15:17, 8 April 2020 (UTC)

I'd be happy with changing This creates a paradox to This seemingly creates a paradox and adding a sentence like, Which, if any, of these assumptions should be abandoned remains a topic of debate. XOR'easter (talk) 23:04, 8 April 2020 (UTC)

[2] "In order to resolve the paradox": which one, the information loss or the firewall paradox? Rolf H Nelson (talk) 22:27, 11 April 2020 (UTC)

Not a good sign when the first sentence is wrong

The article starts with "A black hole is a region of spacetime exhibiting gravitational attraction so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it" and citing the book by Wald. But in the same book, the next sentence says "However this notion is not properly captured by defining a black hole". It's not fair for a so good book to cite it wrongly. The horizon is not about how strong is gravity. For a supermassive BH, gravity could be very weak at the horizon while for a small black hole any object would be destroyed by tidal forces long time before reaching horizon. SO NO, horizon is not about how strong is gravity. In relativity, time is fundamental component, without it, one can't understand. Time is also affected and therefore the future light cone, which rotates toward the interior of the black hole. Once an observer reaches the horizon, his future is inside the black hole. It's not about how strong is gravity but about deforming the causal structure. — Preceding unsigned comment added by 201.241.20.145 (talk) 02:07, 13 April 2020 (UTC)

Please put new talk page messages at the bottom of talk pages and sign your messages with four tildes (~~~~) — See Help:Using talk pages. Thanks.

The first sentence does not say that the horizon is about how strong gravity is. It does not even mention the horizon, so I don't think there's a problem with it. Your objection is covered by one of the following sentences, and further down in the article. - DVdm (talk) 07:19, 13 April 2020 (UTC)

Note that the first sentence does not mention "gravitational force" or "gravitational field" being strong. It says "gravitational attraction" this is purposefully a bit vague, to cover the much more technical description of curvature of spacetime leading to the formation of trapped surfaces and a event horizon, which are accurately (but in precisely) covered by the accessible description "strong gravitational attraction".TR 11:06, 13 April 2020 (UTC)

I don't personally like it either, I'd prefer something like "with a strong gravitational field that nothing can escape from", but the current text is well-sourced, so we should just leave it unless someone has a strong source that words it better. In any case, I don't think it's actually causing anyone to be confused about the basic idea of what a typical black hole is.

There's also some room for a "black hole for laymen" article that explains the causal structure in a more accessible way, either by expanding https://simple.wikipedia.org/wiki/Black_hole or creating an article in the Category:Introductory articles series.Rolf H Nelson (talk) 06:30, 14 April 2020 (UTC)

Note that a statement like "with a strong gravitational field that nothing can escape from" is categorically wrong for the reasons mentioned by the IP above. The gravitational field at the horizon can be quite weak.TR 13:46, 14 April 2020 (UTC)

Sure, but the horizon is not mentioned. - DVdm (talk) 13:59, 14 April 2020 (UTC)

Nonetheless, the strength of the gravitational field has nothing to do with things not being able to escape.TR 16:54, 14 April 2020 (UTC)

But the opening sentence does not mention the gravitational field either, let alone its strength. It looks like Wald gave that line quite some thought . - DVdm (talk) 17:02, 14 April 2020 (UTC)

Exactly, which is why I was commenting that changing it to something like "with a strong gravitational field that nothing can escape from", as was suggested, would be bad.TR 17:28, 14 April 2020 (UTC)

Ok, and good one, this. - DVdm (talk) 17:58, 14 April 2020 (UTC)

Yeah, fair point on that one. Ceoil (talk) 02:46, 16 April 2020 (UTC)

Full protection

Ceoil, Deacon Vorbis, please resolve your dispute in the usual way, through talk page discussion. Thank you. El_C 02:21, 16 April 2020 (UTC)

Its seems to me you dont understand the tools you are wielding. Protection against a two well established editors? Ceoil (talk) 02:44, 16 April 2020 (UTC)

Yes, Ceoil. Established editors do not get to edit war, just the same as newcomers. El_C 02:45, 16 April 2020 (UTC)

Ok, but this is becoming tedious, my original point on your talk stands: if you dont understand the tool or the rules, best say nothing. DVdm, no offence to you at this point. Ceoil (talk) 02:48, 16 April 2020 (UTC)

I realize you wish to make me the target of your frustration, but that makes it neither fair nor reasonable. El_C 02:50, 16 April 2020 (UTC)

i'd prefer if you went back to DVdm's version and lifted full protection; my additions were only matters of style, I thought. You overshot here, with no appreciation of content protection. Ceoil (talk) 02:55, 16 April 2020 (UTC)

I saw an edit war where exceeding 3RR by the participants was a real risk, so I acted quickly. I thought that was to my credit. Anyway, happy to oblige. El_C 02:56, 16 April 2020 (UTC)

Semi-protected edit request on 12 June 2020

In the last paragraph of the introduction please chenge "On 11 February 2016, the LIGO collaboration announced the first direct detection of gravitational waves," with "On 11 February 2016, the LIGO and Virgo collaboration announced the first direct detection of gravitational waves, Geppo.Cagnoli (talk) 09:14, 12 June 2020 (UTC)

 Done: [3]. - DVdm (talk) 09:25, 12 June 2020 (UTC)

It's "shredded", not "shred"

The fourth paragraph contains the word "shred" used as a past tense. This should be "shredded".50.205.142.50 (talk) 15:46, 24 June 2020 (UTC)

No, it's being used as a past participle rather than a simple past tense, and both shred and shredded can be used in that sense. –Deacon Vorbis (carbon • videos) 15:51, 24 June 2020 (UTC)

Doesn't look like its being used as a past participle to me. The sentence: "Stars passing too close to a supermassive black hole can be shred into streamers that shine very brightly before being "swallowed." has the simple sentence "Stars can be shred." The main verb, "can be shred", is present tense in the potential mood which is made with auxiliary verbs plus the infinitive verb form ("to shred" without the "to"). Were you to rewrite the sentence out of the potential mood in the the indicative mood, the main verb "can be shred" would change to "are shred".Tachypaidia (talk) 14:21, 14 July 2020 (UTC)

The infinitive here is "be shred", which is passive, which formed from of the appropriate tense of "to be" and the past participle of shred.TR 15:47, 14 July 2020 (UTC)