70 votes
Accepted

Can gravitational waves pass through a black hole?

No, gravitational waves cannot pass through a black hole. A gravitational wave follows a path through spacetime called a null geodesic. This is the same path that would be followed by a light ray ...
  • 1,609
53 votes
Accepted

If light has no mass, why is it affected by gravity?

Another way to answer this question is to apply the Equivalence Principle, which Einstein called his "happiest thought" (so you know it has to be good). The equivalence principle says that if you are ...
  • 5,270
48 votes
Accepted

Can Newton's gravity equation explain why black holes are so strong?

No you can't and the behaviour of bodies with mass and of light is completely different near a compact, massive object if you use Newtonian physics rather than General Relativity. In no particular ...
  • 131k
41 votes
Accepted

Does General Relativity really predict Black Holes?

Well, yes, but we must be careful with the meaning of "predict". The Schwarzschild solution, developed by Karl Schwarzschild in 1916 [1], is the first closed-form, explicit solution of ...
31 votes

If light has no mass, why is it affected by gravity?

There are a couple of ways one could approach your question: Black holes are regions of space that have been deformed by a sufficiently concentrated mass. Light waves/particles always travel in a ...
  • 1,189
29 votes
Accepted

Maximum spin rate of a black hole?

Since I like math, let's throw some math into this. I'll try to keep it as simple as possible though. Kerr Black Holes A rotating black hole is known as a Kerr Black Hole (named after Roy Kerr who ...
  • 14.6k
29 votes
Accepted

Is it possible to detect gravitational lensing of stars behind the Moon?

Measuring the gravitational deflection of light by the Moon is just out of reach of current observational techniques. The angular deflection caused by the lensing of a distant background object by a ...
  • 131k
29 votes
Accepted

Is there a better formula for gravitation, besides Newton's?

Going from Newton's theory to Einstein's theory is not simple. It's not like you can just add a term to Newton's gravity, like $\textbf{F}=-{GmM \over r^3}\textbf{r} + \textbf{f}(\textbf{r})$ and ...
  • 4,274
28 votes
Accepted

Quantum Mechanics after the detection of Gravitational Waves

No more than the observation of light waves disproves quantum mechanics. Light has properties of both a particle and a wave. At low energies, the particle nature of light is hard to detect: radio ...
  • 103k
26 votes
Accepted

How would "dark matter", subject only to gravity, behave?

What you describe is the standard paradigm in cosmological physics, so it has been studied extensively. The basic consequence of dark matter not having significant nongravitational interactions is ...
  • 1,343
23 votes
Accepted

Was the Sun's gravitational lensing observed in other solar eclipses than the one in 1919?

Yes, observations of this kind are within the technical scope of amateur astronomers. Several groups succeeded in replicating the experiment during the 2017 eclipse that crossed the USA. For example ...
  • 103k
22 votes
Accepted

How do two black holes merge?

The "event horizon" is defined as the point (or surface) from within which light rays can never (ever) reach a distant observer. To find the location of the event horizon implies that you ...
  • 131k
21 votes

Quantum Mechanics after the detection of Gravitational Waves

The impact of this measurement on the status of quantum gravitation is exactly zero. The proper statement of the incompatibility of general relativity and quantum mechanics is that the quantum field ...
21 votes

Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

Birkhoff's theorem is very useful: in general relativity, if you are in vacuum and there is a spherically symmetric gravitational field, then it will be the Schwarzschild solution. This solution only ...
20 votes

Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

If they were spinning they would be distinguishable (in principle), otherwise not. Astrophysical black holes and neutron stars are expected to spin. In the case of a neutron star that automatically ...
  • 131k
19 votes

Quantum Mechanics after the detection of Gravitational Waves

Another question, how can we identify the ripple's origin (let's say that if it's the result from the big bang or another big event)? (I'm just answering this part of the question, as James has ...
  • 2,397
17 votes
Accepted

Have I nearly found the event horizon of a black hole?

This is the Newtonian model of gravity. It is a very good model, it is used for accurate calculating the motion of objects in the solar system to a very high degree of accuracy. However, for very ...
  • 103k
17 votes
Accepted

Doubt regarding size and shape of black hole images published by the Event Horizon Telescope (EHT)

The detail you seek is contained in Johansson (2014). The photon ring around a black hole is not the event horizon. It is the projection of unstable photon orbits that are able to loop around the ...
  • 131k
16 votes
Accepted

How could a neutron star collapse into a black hole?

The scenario you describe may occur. On the other hand it may actually be that neutronisation in a white dwarf is the trigger for a thermonuclear type Ia supernova. You may be misunderstanding the ...
  • 131k
16 votes

How do we know that objects that appear in duplicate or triplicate, etc. due to strong gravitational lensing aren't actually multiple objects?

Perhaps this isn't the case for every scenario, but I can think of at least two instances where this can be determined: Stars In the case of stars, it's pretty straightforward to get the spectra of ...
  • 3,364
15 votes
Accepted

Latest cosmological parameters

Cosmological parameters are measured in a variety of ways, and their values will depend on which measurements you trust the most. The paper you link to (Planck Collaboration et al. 2016) with the 2015 ...
  • 35.6k
15 votes
Accepted

Is the age of the universe relative to an observer's location in that universe?

You are labouring under the misapprehension that how far we can see directly gives the age of the universe. Whilst it is true that the oldest light we can see was emitted some 13.7 billion years ago, ...
  • 131k
14 votes

Can Newton's gravity equation explain why black holes are so strong?

I am not an expert in physics and the explanation of the others is excellent. However, I noticed a flaw in your reasoning which they did not address. You have written: Considering the Newton's Law of ...
13 votes

Why doesn't the vertical light beam get out of a black hole?

There is no "up" direction within the event horizon. Most people get fixated on the speed of light, or energy or whatever. They're like, if light was faster, could it escape the black hole? If my ...
13 votes
Accepted

Is there a closest free-return trajectory to a black hole?

The trajectory of a ballistic body, whether in Newtonian or Relativistic physics depends on the initial energy and angular momentum. The difference is that in Newtonian physics, if the mass is compact ...
  • 131k
12 votes

Does a merging massive binary black hole ‘emits’ more than one gravitational wave?

We can currently only detect gravitational radiation when it is extremely intense: in the last fraction of a second. For example the first gravitational wave detection lasted less 0.15 seconds. The ...
  • 103k
12 votes
Accepted

Why is the ring in this simulation of Sgr A* off center?

The photon ring around a non-spinning Schwarzschild black hole is perfectly circular and centered on the black hole. The photon ring around a spinning Kerr black hole is almost circular (except for ...
  • 131k
11 votes
Accepted

How far should the source be, for the gravitation waves to be visible on Earth?

The waves pass by at the speed of light. So you you would'nt see ripples, they would pass too fast, and remember the waves would be passing through you too. The wavelength was (relativly) long about ...
  • 103k
11 votes

Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

Technically, there would be minute differences due to the gravitational field generated by the mass of the spacecraft tidally deforming the neutron star leading a small response in the gravitational ...
  • 2,113
10 votes

Can gravitational waves pass through a black hole?

Gravitational waves should be lensed by massive objects in a very similar way to light. Light rays (and by extension, gravitational waves) from a distant object, that pass within 1.5 times the ...
  • 131k

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