Questions tagged [black-hole]

Questions regarding points of extremely high mass density, which creates an extremely strong gravitational field from which light cannot escape.

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If two black hole event horizons overlap (touch) can they ever separate again?

Hypothetical question based on my understanding that two event horizons that overlap (touch) can't ever separate again: Imagine a 1 billion solar mass black hole (so the event horizon is massive and ...
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I simply want to ask a question about quantum tunneling as an origin of black holes [on hold]

I found this site after finding a search reference about quantum tunneling (QT). I simply wanted to pose a simple question about whether or not QT was ever considered as a source for black holes ...
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How many stars and planets have been destroyed by black holes since the beginning of the Universe? [closed]

I would like to know what is the estimated/predicted number of stars and planets that have been destroyed by black holes since the beginning of the Universe, 13.7 billion years ago.
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Undisturbed planetary alignment after galactic collision

How do planets still orbit around the empty space where a black hole was after a black hole absorbs the milky way's black hole and keeps moving through space without disturbing surrounding planets ...
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Might the discrepancy between mass and rotation rates, in galaxies, be explained by mass within BHs? [closed]

I'm wondering whether the total mass of a galaxy's hypothetical black holes, that may have each been formed within the gravitational horizons of larger black holes (that are indirectly apparent, ...
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Black hole properties [duplicate]

Black holes are things with immense gravity.Inside black holes gravity is much stronger than any other fundamental forces.But is strong enough to overcome Pauli repulsion?
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Causes of emission of accretion disk

As far as I can see, there are two main sources for the emission of energy from an accretion disk: release of gravitational potential energy of the infalling matter; friction from differential ...
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What is the closest one could get to a black hole and still stand a _realistic_ chance of escape?

This question is inspired by the one asked here: Is there any stable orbit around a black hole? and I note that (though I've heard of these before) there are, apparently, 3 important fundamental "...
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Can a star going supernova while inside a black hole create gravitational waves that could be detected?

This is part of a series of questions exploring black holes and gravitational waves as tools to further our understanding of our universe. Backgrounder: Can a star fall in a super massive black hole ...
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Can a black hole “supernova”?

In layman terms: nothing ever escapes the pull of a black hole, not even light when a large star reaches the end of it's life you get a supernova sometimes the "remains" of these stars can turn turn ...
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Are black holes spherical during merger?

I've been thinking about black holes, specifically during the final moments before two merge. I'm wondering if black holes, or I guess more specifically their event horizons, are always spherical. ...
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1answer
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Question from a non-astronomer /non-mathematician regarding rotation speeds

I have been watching too much TV related to black holes. Most black holes are depicted with a disk of matter that spirals into the black hole. Does the mass and diameter of the disk have a bearing on ...
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What is the coordinate acceleration for pure radial motion?

As seen in this answer and also in this book chapter 6, page 6-10 expression 22, when you are falling in radially from being at rest at infinity your velocity in coordinate time, as seen from a ...
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How does a spinning black hole affect space-time compared to a non-spinning black hole?

I often see questions on this site that only apply to non-spinning black holes and often wonder how the answer would be different for a spinning black hole. As the title says, what are the major ...
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Do photons slow down as they approach the event horizon of a black hole?

So, if a black hole is so dense, that light cannot escape, what happens to the photons as the approach and go past the event horizon (or some other horizon, about which I am ignorant)? Do photons ...
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Is our Universe inside a black hole? [duplicate]

Could the known universe be inside a black hole and it's curvature really be the event horizon of the black hole?
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Ideas about the origin of the “black hole - galaxy mass” relation?

It has been extensively shown that the mass of black-holes located at the center of galaxies scales with several galaxy properties, most notably the stellar velocity dispersion of the stellar bulge, ...
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Does time dilation at the event horizon prevent us from seeing any changes?

If gravity is so strong at event horizon as we assume, and thus time dilation makes time infinitely slow for us, the distant observers, how could we ever observe any events ocurring over time? Wouldn'...
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As matter approaches a black hole, does it speed up?

If so, how do we know it speeds up? Doesn't time slow down as gravity increases? If time slows down around a black hole, is it possible matter doesn't actually speed up?
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1answer
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Would Hubble Space Telescope improve black hole image observed by EHT if it joined array of telesopes?

My question is related to black hole image released in April. As far as I understand idea of EHT, it joins observations from multiple locations to work like one telescope with radius that is equal to ...
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How accurate are the new visualisations of V404 Cygni

A number of pictures and some animations similar to the ones below have had much press recently. Clearly the colours are artificial, but I wondered how accurately the represent the geometry of the ...
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1answer
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How to convert the observed magnitude of a Quasar to it's bolometric luminosity?

How can I convert the observed magnitude to Bolometric Luminosity? I know the relation for the star but should it be same for a Quasar? Basically I want to convert the X-axis of this plot to ...
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4answers
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How exactly does Hawking radiation decrease the mass of black holes?

From what I understand so far, when one of virtual particles crosses the event horizon and the other does not, they can not annihilate each other. The latter wanders off into the universe (btw. is it ...
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If a photon were 1 Planck length away from the event horizon of a blackhole, would it be able to escape the blackhole's gravitational pull?

I understand that one could theoretically replace the sun with a blackhole without affecting the orbits of the planets. This leads me to believe that a blackhole isn't a "cosmic vacuum cleaner" so ...
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Mass of Photon and Black holes [duplicate]

The gravity caused by a black hole is said to be so strong such that even light(photons) can not escape from it. since gravity exist only in between objects with mass, How does a black hole attract a ...
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1answer
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Could an object, assuming possible, escape black hole by travelling above constant speed? [closed]

I am always hearing that after travelling inside a given BH's event horizon, the escape velocity is greater than c, which makes it impossible to escape. Suppose an ship is inside a BH. Assume it is ...
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2answers
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Can gravitational waves pass through a black hole?

As the title says, what happens when a gravitational wave approaches a black hole? I would presume that something interesting happens because of the way spacetime works near black holes but I have no ...
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1answer
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What happens if I were to add angular momentum to a maximally spinning black hole? [duplicate]

I am aware that a "naked singularity" is not possible. However, what would happen if I added angular momentum to a black hole near the maximal angular momentum limit? Does it asymptote?
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4answers
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Black hole density

How does more compression relate to a stronger gravitational pull. Like, when we say that a black hole is a tiny space that has 20-30 suns compressed in it, how does this increase its density and ...
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How does the black hole at the center of M87 look like in the visible spectrum?

I learned here that the picture of the black hole we saw all over the news was a false color image, based on the radio spectrum emissions. How would the black hole at the center of M87 look like when ...
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1answer
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Where is the intervening light in the M87 black hole?

The M87 black hole is at the centre, more or less, of an elliptical galaxy of 1 trillion or more stars. So certainly there are stars and other light emitting objects (emission nebula e.g.) in the ...
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Why does the Event Horizon Telescope (EHT) not include telescopes from Africa, Asia or Australia?

The Event Horizon Telescope seems to include these radio telescopes currently: Image by European Southern Observatory (ESO)/O. Furtak; CC-BY 4.0-licensed, see the source on Wikipedia Commons and the ...
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1answer
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If a black hole does not emit light, how can one take a picture of the black hole itself?

There's some discussion that the image composed by the Event Horizons Telescope is really just an accretion disk. To "take an image" of something, you need the light reflecting off of the surface of ...
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Do the “schwarzschild metric” or the “isotropic metric” fit the Event Horizon telescope data on Messier 87 better?

The "Schwarzschild solution" in "Schwarzschild metric" looks like: $$\text -c^2d\tau^2=-\left(1-\frac{2GM}{rc^2}\right)c^2dt^2+\left(1-\frac{2GM}{rc^2}\right)^{-1}dr^2+r^2(d\theta^2+\sin^2\theta\,d\...
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What is the actual visual characteristics of a black hole?

Is there a safe distance in which a black hole can be observed with the human eye? What is a safe distance? I have seen many computer simulated and artist renditions, and I am not sure if they ...
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2answers
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What does it mean when we say that information is potentially recoverable from a black hole

My understanding is that if the surface of a black hole is holographic, then information is potentially emitted from a black hole, say due to Hawking radiation or some other means. What can say ...
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Why is the ring of light around the M87 black hole bigger than the photon sphere?

Today we know that a black hole represents a region of space where the gravitational forces are very intense, this consequence of a concentration of matter in a very small region of space. On April 10 ...
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Why isn't the relativistic jet visible in the image of the M87 black hole?

I'm referring to the infamous relativistic jet, which consists of matter being accelerated to near the speed of light, originating at the poles of the black hole: But in the image of the black hole ...
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Why not capture also Milky Way's black hole image? [duplicate]

The world has now seen the black hole "close-up" of M87. Besides the recognition to how awesome science has become in the 21st century, I have the following question. Didn't they work also to ...
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1answer
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Why the chosen orientation for the M87 black hole image?

By now we are all familiar with the official image of the black hole in M87: Now, in the universe, as far as I know, there is no up and down, nor left and right. All is relative. Hence my question: ...
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1answer
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M87. What was the black hole before?

10 seconds before the M87 black hole was a black hole, what was it? A star 10 times the size of our solar system?
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What resolution would earth-moon telescope achieve?

Event horizon achieved earth-size telescope by using seperate telescopes around the world to interpolate an image of a black hole at resolution of 60 arcmicroseconds. What resolution could we get if ...
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2answers
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What is the light source in the black hole images?

What is the light source in the black hole images? I've searched the site before asking, as well as tried to google it. But perhaps the answer is buried due to the recent news. My understanding, is ...
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Why isn't the black hole white?

I recently saw the first image of a black hole. As I understood, it is covered with bright, hot matter. In this case, how can we see the black disk (event horizon), instead of a bright disk due to the ...
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1answer
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Why don't we see the gas behind the black hole?

In computer simulations of what a black hole might look like and many artist renderings of black holes, they all seem to show the brightly glowing gas BEHIND the black hole due to gravitational ...
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What description of the image can we expect from the image of first black hole? [closed]

The EHT has published the first image of a black hole. I was wondering what could be the size of the original image of the first black hole and the format of the image captured?
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1answer
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Event Horizon Telescope Data Cleanup

I was wondering how the researchers were able to minimize or neutralize confirmation bias regarding the data collected? As I understand it, the algorithm pruned much of the data, which would make ...
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1answer
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Does the “photo of a black hole” taken by EHT actually depict a visible light-based scenario?

I'm still at my bachelor of electronic and communications engineering, so I'm not an expert of radiotelescopes; however, I surely know that, typically, radio communications are characterized by a RX ...
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1answer
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If blackholes are spherical, what is the prespective of the blackhole image? [duplicate]

If black holes are spherical, so shouldn't it be absorbing light from all the directions? How would one explain the light ring. which seems more like a 2D ring than a sphere?
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2answers
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What part of the EM spectrum was used in the black hole image?

The EHT has published the first image of a black hole. It is the event horizon of the singularity in M87 against its accretion disk. I've been through the reports in the popular press but none ...