Black hole Definition and 999 Threads

Can I bring an old thread back to life? The last post in Gravity for a stellar black hole was in Mar-2008, but I have been looking for That Thread since 2000! Unfortunately for me, it raised more questions than answers. Thanks SamT Woops. The Username "SamT" is already taken, but it's been my...

[Moderator's note: this discussion has been spun off from another thread.] This is probably a silly idea, but I haven't got any reputation to preserve, so I'll mention it anyway. My very limited (and probably very wrong) understanding of quantum theory tells me that until something is...

For an observer far away, nothing ever seems to actually cross the event horizon of a black hole, but to "freeze" right at the event horizon. Does this mean that if we could observe a black hole, we would be able to still see everything that has ever entered the black hole? Would every object...

I saw somewhere a thread about a cow falling into a black hole. I don’t know why a cow, perhaps the OP was thinking about the Milky Way. With the cow example it is not clear to me what we are supposed to see when an object falls towards the event horizon. If time slows to infinity, does the...

OK, so we know that there is a supermassive black hole at the center of every galaxy. But I want to ask where is the mass of a black hole actually. When the black hole is formed and if there is a supernova or hypernova then much of the mass is ejected out then how can we says black hole has a...

Let's say I'm towing a black hole by using a spaceship, and a rope, and a mass that is attracting the black hole near its event horizon. Let's say the mass unfastens at some moment, and I'm watching everything carefully. Obviously I will notice that the mass has unfastened only after a long...

I thought of posting this on astrophysics or general relativity forums since it seems completely classical, but given the extraordinary claim, I am posting here. Note that one of the guys is a notable string theorist. http://arxiv.org/abs/1510.03396v1 Journey Beyond the Schwarzschild Black...

For this we need a thought experiment: imagine you're on a gedanken planet manning a gedanken laser cannon, and it's pointing straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now let's keep you safe in a bubble of artistic licence, and...

My very basic understanding of black holes leaves me with a question about why black holes increase in size, or rather, why does the event horizon increase in size. As I understand it, a black hole is a large amount of mass condensed into a such a small space that the amount of gravity produced...

Homework Statement Muscle can be torn apart by a force of 100,000 N applied across an area of 1 m2. A 10 cm2 muscle therefore will be torn by a force of 100 N. If a student of average size were being lowered into a black hole of 1 solar mass, at about what distance from the hole's center will...

I understand that, as matter approaches the event horizon of a black hole, according to the time frame of someone outside the black hole, it would slow down and, after an infinite time, stop completely at the event horizon. So, if we could observe it, all this matter would be accumulating just...

Let's put an observer hovering near the event horizon of a charged black hole. As the black hole is charged we can change its velocity from zero to 10 m/s in one second. But we can not send a message to the observer in one second. So the observer does not know that the black hole that he is...

Forgive me if this is a dumb question. If nothing gets out of a black hole, how does the gravity get out?

stevebd1 submitted a new PF Insights post Time Dilation and Redshift for a Static Black Hole Continue reading the Original PF Insights Post.

Let's say I encode all the information in some book in a light beam. Then I put a black hole in the way of the beam. Mass and information of the black hole increase as the beam plunges in the black hole. But what if the black hole is moving very fast parallel to the beam? In this case the rest...

There are many videos and articles about this topic (what it looks like if you fall into a black hole). I remember hearing that, inside the event horizon of a black hole, time has essentially stopped for an outside observer. However, if you fell into one that would mean that any amount of time...

Hey, I know that one doesn't work with polar coordinates (t,r,θ,φ) because they don't behave well in the event horizon. But my problem is with raidal null curves, if we take ds2=0 and dφ, dθ = 0 so we have When, if I'm correct, the + sign determine that it's outgoing and the - infalling, so...

Homework Statement The Galaxy has a black hole with about 3 x 10^6 M☉. What is its diameter in AU? Homework Equations Not sure. The Attempt at a Solution 3,000,000 solar mass, but not sure how to figure out the diameter in AU. Let's see...diameter of the sun is 1,000,000km 3,000,000 x...

I have learned that light has a constant speed of 299 792 458 m / s or C and that this speed cannot be changed by anything, how can a black hole "trap" light if this speed cannot change? Is it because time is also trapped, so a second lasts infinitely long?

MTW, p. 924, defines a caustic as a point where a null geodesic originating from the external universe enters a black hole's event horizon, remaining in the horizon afterward for some finite affine interval. (A null geodesic of this type is called a generator of the horizon.) They introduce this...

Dear PF Forum, I have a question in mind. But I'm not sure if this belong to SR forum, cosmology or classical physics. So I post it here. And perhaps as some of you might have known before or thought it over. It's about kinetic energy. Supposed this... A rocket, with a rest mass 1 ton. And the...

I would like to discuss a bit this paper (http://arxiv.org/abs/1508.06577): BMS invariance and the membrane paradigm Robert F. Penna (Submitted on 26 Aug 2015) We reinterpret the BMS invariance of gravitational scattering using the membrane paradigm. BMS symmetries imply an infinite number of...

Bee Hossenfelder was live-blogging from Stockholm Conference on BH info puzzle today Tuesday 25 August. Herewith: http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html The conference is 24-29 August. Hawking presented his idea Tuesday, based on joint work with Malcolm...

Greetings, I am new to this forum and would like to present a discussion. If a miniscule black hole is created in the LHC. Is it probable the LHC is capable of creating more than one black hole during a single event collision? Considering fact and theory provided by credible research. Could...

I'm very new to the understanding of Hawking Radiation. I don't know much about this theory, but I do know that Hawking radiation works on a Quantum scale. I know that with black holes this theory proposes th idea that over time black hole lose mass because of "Spontaneous appearing positive and...

PeterDonis submitted a new PF Insights post Centrifugal Force Reversal Near A Black Hole Continue reading the Original PF Insights Post.

What's the best way to explain why tidal forces for an observer free-falling through an event horizon are finite? My first thought was to say that "gravity isn't a force, it's a curved space-time". On further thought, however, it seems to me that consideration of the Rindler horizon shows...

According to Hawking [1] it is posited that light photons at the event horizon of a black hole must cease to move, and remain motionless for the entire lifetime of the black hole. It is also observed [http://dls.physics.ucdavis.edu/~scranton/LensedCMB/a2218.gif] (and calculated) that the path...

Leonard Susskind talks about Black hole Quantum Complexity in one of his online lectures. I was wondering what you guys on the forums think about this, and what you guys think it means. Here's a link to the video He points out that the complexity increases linearly with time, and at the...

Dear PF Forum, Can we avoid spaghettification for some times, once we're inside event horizon? I choose a rather massive black hole, so the tidal force won't be so big at EH. Mass: 1 trillion solar mass Schwarzschild radius: 2.950 trillion KM What is the gravitational force at EH? I calculate...

Past the event horizon of a black hole, gravity is so immense that even light can't escape. Wouldn't this cause the the gravitons, which travel the speed of light, to be trapped, making a singularity?

Dear PF Forum, I have read a link about big bang time line. Started from time zero, then Baryogenesis, lepto genesis, Planck time then on... http://www.physicsoftheuniverse.com/topics_bigbang_timeline.html I try to make a simple calculation here with Schwarzschild calculator. The mass of the...

Since light is entirely incapable of slowing down, what happens when light approaches a black hole such that it's trajectory passes through the exact center of the black hole? It seems, based on what I currently know, this would mean that the gravitational force pulling on the light would be in...

[Moderator's note: Spin-off from another thread.] I'm sorry, does black hole have surface area? Did you mean the sphere defined by Schwarzschild Radius?

I'm just curious, do black holes have a maximum size? In other words, if it theoretically had an infinite supply of matter to "feed" off of, would the black hole just get more and more massive or is there a point where it can no longer fit anymore matter? Will it just spit out hawking radiation?

Can one create a black hole when already inside the black hole ?

Hello people, I have a question regarding black holes. The way i understand it, black holes form in supernovas, and they occur because the gravitational pull of the stellar remnant is so great that nothing can stop it, and it basically collapses down to a singe point, virtually nothing... Now...

I've been reading 'A brief history of time' and want to know more about how black holes are formed. Please help?

What would happen if you went into a black hole?

Dear PF Forum, I have no background in physics :frown: In http://math.ucr.edu/home/baez/end.html 1. If an Earth size object is left alone (assuming the Sun won't swallow it 2 billions year later). In 101500all of it atoms, oxygen (majority abundant in earth, right), silicon, nitrogen (abundant...

Questions about black holes: Various articles mention that it takes infinite amount of time to observe something pass through the event horizon. Does this imply that the redshift observed from afar would carry on forever, that the infalling object would just become dimmer and dimmer, but never...

We all know from the relativity, that even the light gets into the black hole, so gravitation-gravitons(what is actually graviton?)are stronger than photons in this case!?

I want to know which dimension does the black hole belongs? Can anyone say which force is responsible for the absorption? In case, if the black holes absorbs everything then were the things might gone?Is that everything becomes invisible or just blast into pieces?

Forgive me if I have posted this in the wrong location. I'm trying to reconcile my understanding of spacetime, but am running into a paradox that I'm sure is arising from my own misunderstandings. As you get closer to a black hole, time, with respect to outside observers, begins to slow to a...

Hi all, I am currently reading a paper and they have this statement in the abstract: "If the supermassive black hole Sgr A* at the center of the Milky Way grew adiabatically from an initial seed embedded in an NFW dark matter (DM) halo, then the DM profile near the hole has steepened...

Normally a star with a mass several times that of the sun will become a black hole at the end of the lifetime of that star. Can black holes exist with a mass much smaller than that exist? In other words, are black holes with a mass of Jupiter or even Earth exist? Or even much smaller than that...

Does gravity get destroyed in a black hole ? If the Higgs particle creates mass in the universe and higgs are destroyed in a black hole, then the total gravity in the universe must diminish over time , hence the universe expanding ?

Homework Statement I am preparing a report on black holes and I recently learned about a phenomenon I was previously unaware of: the photon sphere of a black hole. While reading an article on said occurrence (I have now confirmed this on multiple sources) the photon sphere which is the minimum...

Good morning everyone, I'm Giuliano and I would like to know how light behaves in a black hole and because it can not get out. More precisely, i understand that light moves in curved space-time format from the black hole, but once passed within swarzchild radius the photon is expected to impact...

I've been working through Leonard Susskind's "The Theoretical Minimum" lecture series (which are a fantastic introduction to the topics covered by the way) and a couple of his comments confused me when he was covering the Kruskal-Szekeres metric/coordinates in General Relativity. The end of the...