1
vote
2answers
75 views

When we look in different directions in the universe how do we know we're not seeing the same thing?

For my question assume: 1: Big bang happened at a point (I know it happened everywhere) but after that explosion universe started to expand in all directions so it maybe considered to happened ...
0
votes
2answers
26 views

Are combined masses in space, such as galaxies, considered to be uniform bodies? *In addition, a related question about force

If we were to calculate the force that one galaxy exerted onto another, would we consider the individual masses within the galaxies, or the masses of the galaxies as a whole? Do the individual stars ...
1
vote
1answer
107 views

Stress-Energy Tensor

As of recent, I've been doing a bit of self education in GR, equipped with a working knowledge of the key elements of the differential geometry in GR, and in looking at the Einstein-Rosen bridge, I ...
3
votes
1answer
128 views

Why do galaxies “dissappear?”

So, this is a dumb question but a bit of information confused me lately. Before, I figured galaxies were no longer visible by us because their luminosity decreased in an inverse square manner. ...
0
votes
1answer
135 views

Would a collapsing Universe have the density of water?

I understand that the typical density of the super massive black hole is close that of the water. It is also my understanding that this density is not true matter density because the volume used to ...
1
vote
0answers
75 views

Modelling a matter dominated universe collapsing into a black hole

With the FLRW equations we can get solutions for a matter dominated closed universe in which the finale is an ultimate collapse, but this is only in terms of $a$ (the scale factor) and $t$ (time) and ...
1
vote
0answers
51 views

Do wormholes have a side to their path through space?

In theory do wormholes have a side to their path through space? What is there at a point in line with the entry and exit, would anything look different at that point in space? Could a space ant get ...
1
vote
2answers
146 views

Gravitational field has no curl? What about gas discs around stars, black holes, etc.?

So everybody says the gravitational field has no curl, and is not comparable to a liquid swirling around a drain. Observationally, of course, there are many examples of vector fields (which I think ...
-1
votes
3answers
159 views

Can the Cosmological Constant explain an accelerated expansion?

From what I've learned so far, it appears that all models that attempt to explain the expansion of the universe are either based on Lambda-CDM or quintessence. The former support a big bang with ...
1
vote
0answers
67 views

Relativistic Black Hole? [duplicate]

So recently, looking at high energy particles through the lens of General and Special Relativity has peaked my interest. One thing I was considering, using the electron as the first example, is as ...
1
vote
2answers
46 views

Are high redshift masses corrected for relativistic mass dilation? They would appear more massive right?

A distant quasar would be less massive in its frame of reference than our observations would suggest. Are such highly red-shifted objects corrected for relativistic mass dilation?
4
votes
1answer
139 views

What is the effect of gravity on gamma rays?

I read an article about a Gamma Ray burst linked to a black hole. How does high gravity fields affect gamma rays?
-4
votes
1answer
125 views

Recommended book for beginners on advanced science topics [duplicate]

I have a background in engineering so I have some familiarity with basic math and science. I've recently been reading about other topics such as Einstein's relativity and have become interested in ...
2
votes
2answers
87 views

Cosmological models other than FRW

The FRW is a nice isotropic and symmetric metric but I think its assumptions are too many. I was wondering about alternative models. Specifically are there any prominent alternatives that have more ...
3
votes
1answer
667 views

Solving the Tolman–Oppenheimer–Volkoff (TOV) equation

The Pressure of a static spherical object (say star), which has the Schwarzchild metric outside it, satisfies the following differential equation called the TOV equation. ...
7
votes
2answers
545 views

Is the speed of sound almost as high as the speed of light in neutron stars?

Have you ever wondered about the elastic properties of neutron stars? Such stars, being immensely dense, in which neutrons are bound together by the strong nuclear force on top of the strong gravity ...
10
votes
2answers
297 views

Stellar winds from neutron stars

It seems that this question has not really been explored in the literature. Do isolated neutron stars (which do not accrete material) emit stellar wind? If yes, what composition would it have? If yes, ...
1
vote
0answers
87 views

Does quantum Zeno effect play role in astrophysics?

For example, do two galaxies situated in proximity reduce the atom decay rate in each other? What happens with decay quanta escaped to infinity? Does the radius of apparent horizon effect the ...
6
votes
2answers
641 views

Do black holes have infinite areas and volumes?

How to calculate the area / volume of a black hole? Is there a corresponding mathematical function such as rotating $1/x$ around the $x$-axis or likewise to find the volume?
1
vote
4answers
138 views

How do black holes accrete mass?

Thanks to time dilation, a distant observer watching a man fall in to a black hole will only see him asymptotically approach the event horizon. So how do black holes ever get bigger?
3
votes
1answer
192 views

Why are black hole singularities stable?

The Friedmann equations says that huge matter densities lead to huge expansion rates. In Newtonian gravity, two massive point particles separated by an infinitesimal distance will experience an ...
8
votes
2answers
719 views

What is the physical size of a black hole?

Something that's always confused me. How large is a black hole's physical size - not mass? From descriptions, it would seem that the 'singularity' is a single point, but is it really? Say for ...
4
votes
1answer
220 views

How much does electromagnetic radiation contribute to dark matter?

EM radiation has a relativistic mass (see for instance, Does a photon exert a gravitational pull?), and therefore exerts a gravitational pull. Intuitively it makes sense to include EM radiation ...
4
votes
1answer
187 views

models for astrophysical relativistic jets from compact objects

what is the simplest way to understand the physics of relativistic jets? we know that they have axial symmetry with very tight angular spread, presumably aligned with the axis of rotation of the ...
4
votes
1answer
164 views

Simulating a black hole binary system

As part of a project for my degree I am writing code to simulate N-body gravitational interactions, however I have to then use this code to investigate something. Struggling to think of ideas I ...
1
vote
1answer
547 views

Blandford-Znajek process: Why/how does the current flow along the magnetic field lines

Related: How would a black hole power plant work? I have put a bit of commentary enumerating my confusions in parentheses I read in Black Holes and Time Warps (Kip Thorne), that quasars can generate ...
6
votes
2answers
239 views

Black hole collision and the event horizon

Will the event horizons of a two black holes be perturbed or bent before a collision? What will the shape of the event horizon appear to be immediately after first contact?
2
votes
2answers
185 views

Can the implications of dark energy be used to bridge the gap between Quantum Mechanics and General Relativity?

Can the findings of the Physics Nobel Laureates of 2011, namely the overpowering existence of dark energy (vacuum energy) have any implications in the quest the combine Quantum Mechanics and General ...
5
votes
1answer
175 views

Gravitational lensing from an extended body Vs. a point mass

I am interested in gravitational lensing caused by a cluster of galaxies (say it has a diameter of 1 Mpc and mass of $10^{12}$ solar masses). How close must a light travel as it passes by to be ...
27
votes
3answers
972 views

The Pioneer anomaly finally explained?

Pioneer 10 & 11 are robotic space probes launched by the NASA in the early 1970's. After leaving our solar system, an unusual deceleration of both spacecrafts has been measured to be approximately ...
0
votes
3answers
262 views

Calculating absolute speed of a relative object [closed]

Say you pick a point on the Earth. The earth spins at some constant $x (I don't know how fast, sorry). Now, that point has a different relative speed to a fixed point on Earth's orbit as it revolves ...