0
votes
1answer
29 views

What is the power of the most powerful quasar found?

Trying to find an answer to this question, I came across many sources that are in complete in contradiction. For example Wikipedia states that a typical quasar has a power of $10^{40}$ watts while ...
1
vote
1answer
75 views

Infinite number of universes? Black holes are guilty? [closed]

I was thinking, if the space is infinite, what if there are infinite number of spaces, inside our universe? I mean, everyone knows that black holes exist, but nobody knows what happens when you get ...
0
votes
1answer
148 views

What are the conditions around Sgr A* for a space ship trying to plunge into the central black hole?

The possible problems for a space ship near an active galactic nucleus are the following: tidal forces, hot plasma accreting into the black hole and "jetting" out, radiation, and magnetic fields. If I ...
2
votes
1answer
58 views

What happens when Dark Matter comes in contact with the event horizon of a large Black Hole

Josh Hill, 9, Oakdale Elementary has always talked Theory of Relativity and Astrophysics etc., I can answer most but lately he has stumped me and has been begging me to ask a pro, so here it is.... ...
11
votes
1answer
813 views

Why don't the black holes appear black in color in images of galaxies taken from HST?

According to NASA a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area According to the documentary Space Unraveling The Cosmos about ...
0
votes
2answers
47 views

Size of objects and variations in brightness?

My textbook says talking about Cygnus X-1 (the first black hole to be identified as such) has variations in brightens of the order of 0.01 seconds and that this means that it's dimeter must be on the ...
3
votes
2answers
85 views

Smolin on Cosmological selection and neutron stars

Regarding the cosmological selection hypothesis and testable predictions, Lee Smolin asserted the following: "Smolin: I did make two predictions which were eminently checkable by astrophysical ...
7
votes
3answers
864 views

Is it possible that black holes are also neutron stars, but so dark that we cannot see them?

Since the concept of the singularity in a black hole leads to infinite densities, I wonder if it is really certain that black holes exist? Is there a possibility that massive objects (which are ...
7
votes
2answers
312 views

Neutron stars and black holes

The official limits for a neutron star is $1.4 - 3.2\;M_\odot$. But I read that the limit depends on the particular structure of a star to estimate which mass it must have. I also read that neutron ...
0
votes
1answer
58 views

How can we know that a black hole exists? [duplicate]

How can we know that a black hole exists if it attracts both matter and light, and to prove that it exists would need to observe it? It's a very common question but I don't know the answer.
4
votes
1answer
126 views

Supernovae and black holes?

I think i am correct in saying that a supernova ($Type$ $II$) is caused by the collapse of the core of a giant star. This contraction of the core is stopped by the Pauli exclusion principle and the ...
2
votes
1answer
122 views

Is there a connection between exclusion principle and the speed of light?

As far as I know exotic stars are composed of degenerate matter created by the balance between gravity and pressure of exclusion principle and as the mass of the star grows it goes into more ...
1
vote
2answers
110 views

Photons straight into black hole

What happens to a photon shot straight into a black hole? Does it gain infinite momentum before it crosses the horizon? If it has a finite momentum going in, then it would seem that a photon of the ...
0
votes
1answer
137 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 ...
2
votes
1answer
114 views

Why does a star beyond a certain mass limit (Chandrasekhar limit) only become a black hole?

Why does a star beyond a certain mass limit (Chandrasekhar limit) only become a black hole? A star is first made of hydrogen, it undergoes nuclear fussion reaction combining into helium and ...
1
vote
0answers
78 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 ...
14
votes
5answers
3k views

Why does a star collapse under its own gravity when the gravity at its centre is zero?

The gravity at the centre of a star is zero as in the case of any uniform solid sphere with some mass. When a massive star dies, why does it give rise to a black hole at it's centre? I know how to ...
0
votes
1answer
66 views

(Polar jets) Is it possible that black holes radiate substantial amount of the mass/energy they accrete?

Is the amount of energy a black hole emit through polar jets comparable to the mass it accretes or is it negligible? Here I am mostly concerned about the observational findings as opposed to the ...
8
votes
1answer
217 views

Is it expected tha all stellar black holes will be spinning near the maximum allowed $\omega$-velocity?

Using a bit of classical reasoning I'm imagining black hole formation to be much like an ice skater pulling in her arms: Now, the size difference between a star and its black hole can't even be ...
7
votes
1answer
108 views

How many of which particles are in Hawking radiation?

My understanding is that a black hole radiates ~like an ideal black body, and that both photons and massive particles are emitted by Hawking radiation. So for a low temperature black hole, photons are ...
4
votes
1answer
154 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?
1
vote
1answer
118 views

Visual representations of black holes

Some black holes emit jets that are rapidly circling the poles of what appears to be a sphere at the center of the black hole, cf. Fig. 1. Is there really a sphere here and how far (relative to the ...
11
votes
2answers
1k views

What happens when the black hole at a galactic core eats the galaxy? [duplicate]

I'm making several assumptions, not sure if any are correct: there is a black hole at the center of a galaxy the black hole is eating the galaxy Eventually the galaxy will be gone, right? Has ...
1
vote
1answer
519 views

Do all black holes spin in the same direction?

My question is as stated above, do all black holes spin the same direction? To my knowledge, the spin in the direction of the spin of the matter that created them. Another similar question was asked ...
69
votes
7answers
7k views

How can a black hole produce sound?

I was reading this article from NASA -- it's NASA -- and literally found myself perplexed. The article describes the discovery that black holes emit a "note" that has physical ramifications on the ...
4
votes
2answers
96 views

What reason(s) exist to suppose that all degeneracy pressures can be overcome in Black-Hole formation?

In models of stellar collapse to a black hole, it is a given that density increases without bound towards a singularity. Electron degeneracy I get. Neutron degeneracy I get. I assume there's some ...
6
votes
2answers
665 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?
4
votes
1answer
97 views

NGCC 1277— a recoil ejection?

Recent calculations agree that a merging pair of supermassive black holes can emit enough gravitational waves to eject themselves from a galaxy. Could NGCC 1277, a small galaxy with a 17 billion ...
4
votes
2answers
473 views

Does the Chandrasekhar Limit scale for a Black Hole?

No physicist/astrophysicist I; All I know about the Chandrasekhar limit is that it apparently limits the mass a star may survive, beyond which it degenerates to a neutron star, or a black-hole. Does ...
2
votes
2answers
110 views

A thought about Quasars

If Quasars are "beams" of energy exiting a super-massive black hole, in order for them to get through the black-hole's event horizon, they'd have to be traveling faster than the speed of light. My ...
1
vote
4answers
144 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
196 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
748 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 ...
2
votes
1answer
191 views

When would the proposed black hole at the centre of Milky Way gulp in our solar system? [duplicate]

I've heard and read that our solar system lies near to the peripheral region of the Galaxy. Then accordingly we would have a greater probability of sustaining to eventual gulping down by the ...
6
votes
1answer
269 views

Why do the stars in the galaxy core move so fast?

There are a bunch of stars orbiting the black hole in the center of our galaxy. These stars move at huge speed. Why do we see this? Why do the black hole not impose any noticeable time dilation on ...
6
votes
1answer
120 views

What prevents stars in globular clusters from merging over time to form a black hole?

Globular clusters are apparently very very old, and the density of these clusters appears to increase as one approaches the center of a cluster. Orbits are bound to be chaotic, since there is no ...
4
votes
1answer
165 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
561 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
243 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?
4
votes
1answer
168 views

Why can't a stable star have radius 1 < r < 9/8 its Schwarzschild radius?

From http://www.spacetimetravel.org/ssm/ssm.html : A mass of 1.78 [in geometric units] corresponds to a ratio of radius to Schwarzschild radius of 9/8. Theory predicts that a smaller ratio is not ...
1
vote
1answer
164 views

Supermassive Black Holes = expansion origin?

(Sorry, couldn't resist the title) An article on Physics Today brings news that there is a new record for largest black hole (not) seen in space, some 300 million light-years away. It hints at ...
11
votes
5answers
1k views

Anti-Matter Black Holes

Assuming for a second that there were a pocket of anti matter somewhere sufficiently large to form all the type of object we can see forming from normal matter - then one of these objects would be a ...
2
votes
1answer
24 views

Would the time dilation from being in low orbit around a black hole delay/slow the effects of quantum tunneling?

If quantum tunneling will cause rigid objects like rocks to rearrange their atoms into a slow-moving liquid-like state in ~10^65 years, could an object delay this fate through time dilation in a low, ...
7
votes
1answer
90 views

Where do the bipolar jets of black holes come from?

How are they formed? And why are they so bright?
9
votes
3answers
890 views

Can black holes actually merge?

If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a ...
1
vote
1answer
605 views

Has Cosmological Natural Selection been disproved?

I've been reading Lee Smolin's Life of the Cosmos. Great book and it makes a lot of sense that the conditions in black holes are the same as conditions at the big bang. Question is, has his theory ...
6
votes
3answers
458 views

Black holes in a head-on collision

Assume two uncharged non-rotating black holes traveling straight at each other with no outside forces acting on the system. What is thought to happen to the kinetic energy of these two masses when ...
1
vote
1answer
337 views

How is the mass of black hole at the center of our galaxy measured?

I've been watching a video about dark mater and a lot of the mass is missing in our universe. Astronomers got to this by measuring the speed that stars orbit the center of the galaxy and when they did ...
9
votes
3answers
548 views

Evidence for black hole event horizons

I know that there's a lot of evidence for extremely compact bodies. But is there any observation from which we can infer the existence of an actual horizon? Even if we are able to someday resolve ...
2
votes
5answers
933 views

Is there a black hole in the centre of the Milky Way?

Is it true that the whole galaxy is actually revolving, and powered by a black hole? Has it been proven, and if it is true, how can our solar systems actually keep up the momentum to withstand the ...