Black holes Definition and 1000 Threads

Primordial black holes as a dark matter candidate has been ruled out - http://www.nature.com/news/search-for-primordial-black-holes-called-off-1.14551

Why is there a large Shapiro delay when a light beam passes a black hole? Coordinate velocity of the beam is slowed down in a gravity field, except for the straight down component of the coordinate velocity? Some part of the trip takes a long time anyway.

This paper, http://arxiv.org/abs/1402.3055 Black Holes, Firewalls and Chaos from Gravitational Collapse, reminds me why it is risky to get too close to a black hole. The authors suggest some the paradoxes posed by black holes may be a consequence of the cosmic censorship hypothesis. I may have...

The nuclear explosion occurs when the nucleus of atom of Uranium (of Plutonium) are split in two pieces by neutrons. These two pieces are repelled from each other due to (the same) positive charge; these pieces are moving quickly between other Uranium atoms, colliding with them. These collisions...

Yesterday, I read about Hawking's new proposal regarding the firewall paradox. A more general thought about standard black holes occurred to me. Black holes including stellar black holes are of course always presented as if the event horizon is an invisible barrier, which the unfortunate...

Hawking Says, "There are no black holes." More: http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583

In a recent paper Steve Hawking is reexamines black holes.

I've posted a few threads over the years questioning the existence of black holes, and the response has been unequivocal defense of them... http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583

According to general relativity, if a remote observer monitors an object falling onto a black hole, (s)he will never see the moment when the object crosses the event horizon. Due to the time distortion, the falling object will hover over the event horizon forever. With that in mind, how...

It looks like the case for primordial black holes as dark matter is drawing to a close: http://arxiv.org/abs/1401.3025, Exclusion of the remaining mass window for primordial black holes as the dominant constituent of dark matter.

Since black holes have a temperature, and emit (Hawking) radiation, do they also exert a radiation pressure on things? Say the sun was replaced by a gravitationally equivalent 1 solar mass black hole, what would be the radiation pressure felt by the earth?

I was arguing today with a friend and the argument seemed pretty pointless because we had nothing to back up our facts with, so I thought about hearing your opinion(s). Do black holes violate laws such as the conservation of matter + conservation of energy? I'm currently leaning towards 'yes'...

If we define the density of a black hole to be it's mass divided by the volume within it's event horizon then as the mass of a black hole increases it's density decreases. At some point the density would be equal to the ambient mass density of the universe. Can we correctly consider ourselves to...

Do we have any evidence that either: 1. There exist stellar black holes which orbit supermassive black holes in the centers of galaxies, or 2. There exist black hole pairs which orbit each other, around their shared center of mass?And if the second scenario were to exist, what would happen...

Dark matter build up near or inside Black holes, thoughts ? I can see it making a real mess of the motions and energies of normal matter in and around a black hole or other very dense body that confines dark matter to a small adjacent region. Unslowed by frictional forces...think angry...

Can they exist? What happens when an antimatter black hole and a normal black hole collide?

Hi, I had posted wanting a specific question answered and it was closed b/c i kept repeating my thoughts to try and get an answer. I'm not an expert, so I was wondering if any of you intelligent folks could enlighten me. I am not asking for a crash course on black holes, which is what i...

Hi guys, Simple question for my first post. If nothing escapes Black Holes, how come they're such massive gravity pools? While I can accept that in certain cases the gravity may come from all the mass near the event horizon that did not yet got through (center of Galaxies where it...

I have a couple of questions I cannot find a good answer to in the internet, so I ask you guys. I have heard about singularity as a infinite small point with infinite gravity - I talk about what I assume is the center of black holes. The scientist are talking about quantum gravity - the...

Sorry to have such a broad subject line but I was in a contimplative mood yesterday and the mind was wondering and pondering… From the publication of Sir Isaac Newton,”Philosophiæ Naturalis Principia Mathematica”, the science world has been challenging the findings around gravity proposing...

It's confusing to me how black holes can conserve angular momentum in relativity. In order to define rotation, there needs to be a 1 dimensional line that represents a radius. Considering that a black hole singularity has no dimensions, it seems impossible that a singularity, and hence a black...

If seems to me that the conditions in the early universe which led to the activation of the Higgs field might be found inside a black hole, but in reverse. This might explain the mystery of infinite density inside a black hole, uniting Gen Rel and QM. Might a black hole then be a baby universe...

From a distant frame of reference a falling object never reaches the event horizon due to time dilation. If I drop a meter stick into a black hole lengthwise I should see both ends of the stick getting asymptotically closer and closer but never reaching the horizon, thus the stick should appear...

Einstein's field equations are time invariant. So is it conceivable that a reverse black hole can exist i.e a "white hole"? Or would the second law of thermodynamics prevent such a thing?

In Professor Susskind's lecture 7 on Classical Physics, he discusses Liouville's Theorem. He said that a consequence was that points in the phase space can not coalesce and lose their identity. In Professor Susskind's book, Black Hole War, he discusses why destruction of information at the...

How much is it feasible for us to send some probe/s to the event horizon of a black hole? Perhaps Voyager will arrive at the centre of our galaxy, where if I remember correctly there's a massive black hole. How much time will that take? Probably Voyager will collapse way before arriving at...

Till sometime it was believed that Black Holes were impossible to create ( made by men ), now some theories which were added to the Standard Model show that the Particle Accelerators having energy levels of TeV can actually produce black holes ( like LHC ) ! Okay but now they are unstable...

A thought experiment. C is considered to be a constant speed, that can not be exceeded. Once light passes the event horizon of a black hole however, the gravitational pull is strong enough to exceed, C. This is indicated by the supposition, that not even light can escape the event horizon of...

Hey guys, I was reading that even light can't escape black holes due to the huge gravitational force which they have. I have been mulling it over for awhile now and I am still stumped. How can a force dependent on the mass of the two bodies act on a body-light/photons which have no mass?

Gravity is zero at the center of the earth. how come the same set of equations predict the gravity to be infinity at the center of a black hole? where does the singularity really come into picture? how is a black holes center different from Earth's center?

If two black holes with equal mass were to collide when they reach the point where their respective centers are at the schwarzchild radius of the other black hole could the spacetime distortions caused by their masses cancel out in such a way that matter/energy could escape along the plane of...

In a very simplified, very elementary description: Black holes (AFAIK) suck in huge quantities of light and matter and compresses matter into a singularity. The big bang (AFAIK) was the start of our universe through which huge quantities of energy and matter exploded from a singularity...

We know that DM interacts gravitationally with ordinary baryonic matter, so we should assume that any DM particles close enough to a black hole will also fall into it, shouldn't we? If so we should assume that black holes must have some DM inside them, perhaps impossible to estimate in which...

similar to the rough picture of how BHs radiate if I put a proton next to a BH can one of the quarks be absorbed into the BH and the other two escape? I don't really understand confinement very well but does the confinement picture change next to BH horizon?

Im a little confused...If a black hole has a true point of singularity how does it have magnetic poles, and how does it have jets of charged particles shooting out from its poles,how does this escape the event horizon if light cant? are black holes real?

Now I thought about this while writing my "electric field strength ' question , as it was about has the electric field got an upper limit of strength and the answer is that it hasn't (theoretically) then I thought the same thing about gravity. Does gravity have an upper limit to it's...

Sen 2013 says, How serious a problem is this for LQG? Does this mean that LQG doesn't have GR as its semiclassical limit? Does that mean it's a dead theory, or maybe just that it needs to be modified? Is the technique using Euclidean gravity reliable? Since I'm not a specialist, I'd be...

Here's a quote by Modred from another thread: https://www.physicsforums.com/showthread.php?t=683377 My question isn't about the Hawking radiation part of the statement, its about the "uncharged non-rotating black hole" part. how do we know if a black hole is charged, what it's charge is...

I have just joined this forum as I am curious to discover from experts if my idea is physically possible. Once you pass the event horizon of a black hole nothing can escape as the space time "fabric" is moving into the black hole at equal to or greater than the speed of light. But I hear from...

I was just reading upon black holes, collision and how it bends space and time.. I know for a fact that time stops after the event horizon, but during the collision of two black holes, can the gravity 'overlap' between them to make it strong enough to bend space which in result be enough to...

Hello everybody, I am a first year physics student and I've got two more questions. Assuming that particles in a black holes event horizon have huge kinetic energy, if they collide, can't they create a black hole? I am asking that, because if we have a probability or pontentially be able to...

Hi, One can register waves of light. Is there anything known different then stars where we receive information from? Say black holes? I really guess.

had a thought. suspect that i am wrong but not sure where. no idea of the maths involved but suspect As an object approaches the speed of light relativistic forces come into play – effecting time dilation density etc Can the same theory be rearranged to show that As you approach the density &...

They have to have some color, yeah?

Nothing can escape a black hole, so as an object enters the event horizon, the atoms currently inside the black hole wouldn't be able to bond with the atoms currently outside of the black hole, causing it to sever. But I've never heard of any physicist saying that this would happen, so I'm...

A couple of quick questions after watching a video on the helectic model that the solar system follows on it's course around the galactic center. Please bare with me these maybe idiotic questions. A) Are black holes bound to the spin of the galaxy or do they sit in place on the galactic plane...

Hi all, I was (superficially) reading about the information loss paradox. Of what i understood it's based on the complete evaporation of the black hole via hawking radiation, so in some sense all the energy of a black hole will eventually become radiation. The following question immediately...

I was wondering whether anyone could provide an explanation as to why when two particles are created near the event horizon, only the negative energy particle is captured by the black hole, and the positive particle travels outward and is seen as Hawking Radiation. I have read numerous posts...

I've seen many examples that an observer witnessing an object approach the event horizon will see it slow down to a point where it never seems to cross. Why then do we not see "everything" that has crossed into this horizon frozen in time?

Hello, So i have heard that virtual particlees just pop-in and pop-out of existence, but if a black hole is near those particlee one of the pair of the virtual particlees gets sucked in. So what happens to the other particlee?