The Stack Overflow podcast is back! Listen to an interview with our new CEO.

Questions tagged [black-holes]

A black hole is a volume from which matter cannot escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

Filter by
Sorted by
Tagged with
0
votes
0answers
19 views

Path of free fall in Schwarzschild coordinates (superior at realease speed)

I'm a new member on StackExchange. I'm french and my english is awfull, so I beg you to excuse me and I hope you can understand my question anyway… I'm looking for a very precise equation for free ...
0
votes
0answers
19 views

ZAMO's trajectory near a Kerr Black Hole?

sorry for the "generic" question, just that the last month I have been studying GR from 0 and having problems understanding some of the concepts. Anyways, to the question I wanted to ask: From my ...
0
votes
0answers
15 views

Query concerning black holes [duplicate]

What information can be conveyed from a black hole about the substances and radiations it absorbs into it's singularity.
-1
votes
0answers
25 views

Heuristic physics journals? [on hold]

I am in the last year of a Phd about perturbations in General Relativity --probably also the year of physics in my life-- and I am searching for a refereed journal in order to know if some intuitions ...
-1
votes
1answer
59 views

Black hole Travel [on hold]

Asking out of curiousity. All answers appreciated. You have a machine that generates micro black holes on the outside of it which evaporate quickly and then are immediately generated again upon ...
1
vote
0answers
31 views

Can we measure the amount by which LIGO black hole mergers warp space itself, relative to the mass of the merger?

In our day and age we can calculate the mass and maximum volume of a black hole. With LIGO we can also now calculate by how much is space warped, relative to the distance to a black hole merger, such ...
-3
votes
0answers
28 views

Affect of walking upto and beyond lightspeed [closed]

Setup: a giant planet rotating at the speed of light(L) + 1m/s at its equator (E) Assume at E ± 1m the speed of rotation is L Also, at both the South and North Pole the rotation is 0m/s such that ...
0
votes
0answers
17 views

A Belinski-Khalatnikov-Lifshitz (BKL) singularity

In general, if the perturbed Friedman model behaved according to the second law, Sir Penrose speculated that numerous black holes would merge and collapse, resulting in one final singularity - Very ...
4
votes
1answer
83 views

If I surrounded a black hole with gravitometers and observed the gravitational field as mass passed the event horizon, what would I observe?

By surrounding a black hole with gravitometers I would be able to get a 3-D map of the gravitational field. If I observed this field as an object approaches the event horizon, what would I see? Would ...
2
votes
2answers
89 views

Why does a black hole have much entropy?

Is that just an assumption by Bekenstein etc? For example, what is the different states a non-rotating primordial black hole can be in?
0
votes
1answer
25 views

What force(s) comparable to material and acoustic damping dampens the ringing of merged black holes?

The "ringdown" that was detected after the merger of two black holes by LIGO in 2015 has been compared to the damping of a rung bell. Why doesn't the merged black hole ring perpetually? What force ...
-1
votes
1answer
54 views

Could it be really true that light can't escape from a black hole if we illustrate it with geodesic lines?

If we consider the black hole with geodesic lines, as in this illustration of geodesic lines, source of image : https://blogs.futura-sciences.com/e-luminet/2015/01/20/black-hole-illuminations-13-...
0
votes
1answer
35 views

Radial null geodesics in Schwarzschild de Sitter space

I am currently studying the geodesics of different type of spacetimes and I'm not sure if I'm doing it in the correct way for Schwarzschild de Sitter space (SdS). The metric in SdS is given by: $$ ds^...
0
votes
2answers
84 views

Direct derivation of point-like particle metric in GR

The usual way to derive metric of a point mass in general relativity is (to my knowledge) based on assuming specific form of the metric that reflects spherical symmetry and independence on "time" (...
0
votes
0answers
28 views

Inflation to extract information from black holes

Suppose inflation were to occur for some brief period of time in the region of a black hole singularity such that the density decreased below the Schwarzschild radius. Wouldn't this mean we can get ...
0
votes
1answer
85 views

What are black holes made of? [duplicate]

I did some research and found that an earth-mass black hole, has theoretical mean density inside the Schwarzschild radius about 4•10^17 kg/m³. This is well within density of neutron stars which are ...
0
votes
1answer
75 views

Black hole wave function

Does a black hole have a wave function? Matter falling into a black hole has a wave function. Is the wave function of this matter destroyed or converted to information on the surface of the black hole?...
2
votes
2answers
523 views

What would Happen if a Primordial Black Hole, with 5-10x time the mass of Earth, were to fall into our Sun?

So lately i heard of this theory that planet 9 might be a Primordial Black Hole (PBH) with 5 - 10 times the mass of Earth. I was thinking to myself, what would happen, if such a PBH (if it even exists)...
7
votes
4answers
547 views

Very Massive Relativistic Body [duplicate]

You're observing a massive object (probably a neutron star), and it is moving at a significant fraction of the speed of light relative to you. The mass of the object is just below the mass necessary ...
0
votes
0answers
42 views

Does space have inertia or mass regarding rotating black holes?

As I understood when a astronomical object such gass, planet or star reaches the proximity of a black hole it doesn't exhibit stright motion but a spiral aproximation towards the collapsed body of ...
2
votes
1answer
61 views

What is the expected size of primordial black holes?

I often see it implied that primordial black holes tend to be small compared to stellar masses; Since primordial black holes did not form from stellar gravitational collapse, their masses can be ...
0
votes
0answers
51 views

What is the black hole information paradox?

What is the black hole information paradox? My question is about the problem of whether information is lost when something falls into a black hole. Is information eternal? What about if a book falls ...
1
vote
0answers
51 views

What would the eternal black hole look like?

The white hole and black hole regions in a Kruskal diagram are said to be actually two different locations. Given the problems with white holes it might be a silly question but, hypothetically, what ...
3
votes
1answer
92 views

Where is the black hole information paradox?

If an object falls into a Schwarzschild black hole and a distant observer watches, they see the object fall slower and slower as it approaches the event horizon, until it is "frozen." (To the observer,...
47
votes
4answers
8k views

Why is matter-antimatter asymmetry surprising, if asymmetry can be generated by a random walk in which particles go into black holes?

My understanding is the early universe was a very "hot" (ie energy dense) environment. It was even hot enough for black holes to form from photons. My second point of understanding is that black ...
0
votes
2answers
55 views

Why do Type II supernova happen? [duplicate]

I am an engineer and not a physicist. I am unable to understand why SuperNova happen. I understand that when the core is composed of high atomic number of elements like Iron and further fusion is not ...
0
votes
1answer
45 views

Photon near a black hole - find distance of closest approach from impact parameter

I have the equation relating the impact parameter $b$ to the distance of closest approach $R$. $R^3 - b^2R + 1 = 0$ which can be solved in python. I have a given $b$ and have to find $R$. however, ...
-4
votes
0answers
53 views

Black hole singularity with zero curvature (do you feel weightless)?

As described by GR, at the center of a black hole, may lie a gravitational singularity, where the spacetime curvature becomes infinite. https://en.wikipedia.org/wiki/Black_hole Though, by the ...
2
votes
1answer
72 views

Why is the temperature of a black hole given by $T=E/2S$?

Naively, I would imagine that $$ T = \frac{E}{S} $$ However, for a black hole, $E=c^4 R / 2G$ and $S= A k c^3 / 4 G \hbar $, which yields $$ T = \frac{E}{2S} $$ Is there a simple explanation for the ...
0
votes
1answer
57 views

Relation of specific angular momentum $h$ with velocity and impact parameter for massive particle?

I am computing the path of an incoming massive (!!) particle with speed $v$ far from the black hole in the schwarzchild metric. To determine its path, i need to input the specific angular momentum ...
1
vote
1answer
126 views

Can a straight rod exist next to or inside a black hole?

A black hole is defined as a part of spacetime where gravity is so strong, that spacetime curvature reaches extreme levels. Not even light can escape. https://en.wikipedia.org/wiki/Black_hole Now as ...
-3
votes
1answer
60 views

Can black holes really evaporate? [duplicate]

Stephen hawkings black hole evaporation theory assumes evaporation of black holes by losing mass through virtual particle radiation. As far as i know, the theory isn't based on mathematical ...
1
vote
1answer
31 views

Teukolsky (Bardeen-Press) equation ingoing coordinates

EDIT: I can't seem to delete this question, so I've posted the solution below (I must have made an algebra error-someone checking all this would still be appreciated!). I've left the question as is. ...
0
votes
0answers
54 views

Unified theory of gravity [duplicate]

I have heard that a lot of times, but I have never completely understood what is a force theory unified with quantum mechanics, and also, why do we need this kind of gravitational theory to fully ...
-2
votes
0answers
22 views

If objects slow down near a black hole, doesn't that mean the black holes won't absorb it until later? [duplicate]

First off, black holes grow (and also not die) by consuming matter, right? And if people (or any object) were to get close to a black hole, time would slow down for them which means they would ...
1
vote
1answer
60 views

Measurement postulate and black hole information paradox: are they related somehow?

The measurement postulate states that whenever we make a quantum measurement, we select (projection) from the general superposition state a single pure state. Thus, as a general quantum state is a ...
3
votes
1answer
106 views

Newtons law of gravity universal?

Im a bit puzzled about the video from “One Minute Physics” claiming that Newtons law of gravity is not universal, but breaks down on very heavy objects and are not really confirmed on very light ones. ...
0
votes
0answers
32 views

Relativity paradox with extreme speed [duplicate]

Consider: The supermassive black hole in a galactic core. A neutron star of nearly maximum mass does a very close flyby (remember, galactic black holes don't have the incredibly vicious tides of an ...
0
votes
0answers
30 views

AGN accretion disk double peak explained?

I have a question to the following lecture: https://ned.ipac.caltech.edu/level5/Fabian4/Fab2_2.html In Figure 3 it says that a narrow annuli of a Newtonian disk should alrdy show a double peak ...
1
vote
0answers
26 views

About black holes paradox [duplicate]

About the information paradox in the black holes, isn't it possible in principle, that the "singularity" itself doesn't really exists, and its just the horizon plane, where the particles that falls ...
4
votes
1answer
225 views

Are black holes bound to merge once their event horizons touch? [duplicate]

Even if they move toward each other at relativistic velocities and not head-on? I looked at questions Black hole collision and the event horizon and Dynamics of Event Horizons between head-on ...
0
votes
1answer
106 views

What is exactly rotating in a rotating black hole?

I have read this: https://arxiv.org/abs/gr-qc/9404041 In General Relativity the black hole solutions which have so far been found form a four parameter family called the generalized Kerr-...
0
votes
0answers
21 views

Black hole surrounded by black holes [duplicate]

Is there any configuration of black holes that surround a central black hole that could lift it out of the singularity due to net effects on space-time? Perhaps a sphere of black holes of equal mass ...
-2
votes
0answers
38 views

What happens if we merge a black hole and a white hole theoretically? [duplicate]

Einstein commented about the merging of two black holes to form a larger one in his theory of relativity. Also, theoretically presence of white holes is being proposed. So what will happen during the ...
1
vote
0answers
72 views

What would be the properties of an anti-black hole (concentration of negative mass)?

What would be the properties of an anti-black hole (concentration of negative mass)? Would it emit radiation? Would time go infinitely fast on its surface?
0
votes
1answer
81 views

Silly doubt on penrose diagram for evaporating black hole

This question is based on the naive ideia of evaporation of a black hole stated as, After sufficient Hawking emission the black hole loses it's mass and therefore it's area, until, as a result, the ...
0
votes
1answer
76 views

Black hole mass

It has been taught to us that since the black holes have finite mass, their gravitational force is also finite, which totally fits. The Black hole anyhow has a singularity at it's center which is ...
-1
votes
1answer
32 views

What is the significance in determining the mass of a black hole? [closed]

Was just wondering the importance of the mass of a black hole
3
votes
0answers
51 views

How can the interior pressure of compact objects affect cosmology?

This paper suggests that dark energy concentrated in black hole interiors (they use an unconventional BH model) could act like a cosmological constant. Their claim is that to calculate the equation of ...
3
votes
5answers
283 views

Is it theoretically possible to escape a classical black hole with force?

A stone being thrown from the surface must have a velocity of $11.2$ km/sec if it wants to escape Earth's gravity. However, a stone that has a constant force being applied on it need not have an ...