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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Could a black hole have multiple event horizons?

If a blackhole is huge within rather than tiny (only its compressed expression appearing tiny to outsiders, so a gravity well of increasing depth, and thus increasing space), couldn't it have layers ...
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Could "gravitational atom” black hole be detected using observation of gravitational microlensing?

D. Baumann et al., published the article hypothesizing existence of "gravitational atom” black holes (not sure whether those are just stellar ones or also those could be supermassive black holes ...
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Could primordial black holes explain the SMBH in the galactic centers?

If there were enough primordial black holes (with the right mass) they could explain dark matter. Could they explain the gargantuan monster holes in the center of galaxies?
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How would a balloon structure of a universe look if we collected all mass together in a small region?

Imagine a universe with an inflating balloon structure of spacetime. Matter is distributed uniformly. Now somehow we manage to collect all matter together within a small volume. What would happen to ...
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What's the proper shape of a black hole?

When we observe a circle we see a different shape than someone moving with high speed relative to us. They see an ellipse. Still we say the proper shape of the object is a circle. Now a black hole ...
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How does a black hole look like independently of coordinates?

Observing a black hole from far away, far it looks as if infalling matter accumulates on the horizon. If one falls in though, there is no horizon at all (or it always stays in front of you). Which ...
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What does it mean that the radial coordinate becomes the time coordinate behind the horizon?

The time and radial coördinate change are exchanged with one another behind the black hole horizon. So even stating that it's happening behind the horizon is misleading. There is, as a figure of ...
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Is V616 Monocerotis the closest black hole?

Now that HR 6819 has been found not to be a black hole after all, does that currently leave V616 Monocerotis as the closest known stellar mass black hole?
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How can we see black holes collapse if time inside the event horizon is infinite?

My understanding is that if you fell into a black hole, i.e. crossing the event horizon time would be speed up infinitely fast. This means I could see my whole galaxy die, new blackholes develop and ...
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Is the center of our galaxy, the Sagittarius A* black hole a former star?

If a black hole comes from a dying star, do we have a record or proof that our galactic center was once a huge ball of burning plasma? I'm not an astronomy student.
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Why is the ring in this simulation of Sgr A* off center?

In the recent releases of images of Sgr A*, simulated versions of what they expected were included along side the actual images they were able to get. What confuses me about these simulated images (...
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Difference between NSBH and BHNS mergers

What's the difference between Neutron Star-Black Hole Merger (NSBH) and Black Hole-Neutron Star Merger (BHNS)? Are they the same names for the same events or is there any difference between them? I ...
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Black hole magnification factor

Given a black hole of mass $M$ which has a distance $D_1$ to Earth and $D_2$ to a galaxy being magnified, what is the magnification factor? And a follow-up question: Does it magnify across the ...
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Is a black hole really a neutron star with a gravitational time dilation factor of 1.0

Here's why I'm asking. The gravitational time dilation factor at the surface of a star or planet can be expressed as $$gr/c^2$$ In theory, the same equation should apply to the gravitational length ...
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Using Einsteinpy to plot the precession of a star orbiting a black hole?

I am currently trying to code the precession of a star orbiting around a black hole, the issue I am having though is that I have no clue what the values are and what they mean in the code, if anyone ...
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Doubt regarding size and shape of black hole images published by the Event Horizon Telescope (EHT)

The recent publications of the images of black hole shadow by the Event Horizon Telescope collaboration prompts us to study black hole images in more details. According to the no-hair theorem, the ...
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Time dilation if an asteroid and a small black hole entered a larger black hole?

For an outside observer, everything moves slower the closer it is to a black hole's event horizon, even photons, due to the black hole's time dilation. We also know that when two black holes collide, ...
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Could Hawking radiation turn a black hole back into a star?

Would a black hole after eons of losing mass due to Hawking radiation, eventually turn into a burning star again? As it’s pressure will no longer be overwhelmed by the gravity it once had and through ...
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Declaring of 3C273 as a quasi-stellar object

I am currently reading A Brief History of Time and chapter 6 about black holes. Now, here it says He found it too large to be caused by a gravitational field: if it had been a gravitational redshift, ...
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Are Buckyball-sized black holes possible?

The first item is the basic question; the subsequent items build upon it if it's possible. If these need to be broken into separate questions, I can do that, but they're pretty tightly related. Is a ...
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How is it possible that a Big Bang happened instead of becoming trapped as a Kugelblitz? [duplicate]

I was reading about Kugelblitz on Wikipedia, and it says that if enough energy gets concentrated it leads to a black hole (from where nothing can escape - supposedly). So, if during the Big-Bang, when ...
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Can I ever reach the singularity in a black hole? [closed]

Let us say hypothetically that I am able to survive a fall down a black hole. Now, time dilation exists with respect to the external observer (if I am not mistaken) such that I appear to slow down as ...
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4 answers
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Why is there no black hole-like activities inside a massive star?

Black holes are very dense objects in our universe, where a star that is several times more massive than our sun is compressed within a few kilometers. And here, the intense gravity of the black hole ...
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12 votes
1 answer
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Is the initial gravity of the black hole the same as the mass of the object that created it?

Is the gravity of a black hole the same or more than the original star that created it, before the black hole gets more matter? Is the gravity proportional to the initial mass?
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If the Sun was replaced with a sun-mass black hole, would it be visually detectable?

Assuming it had no accretion disk, could we still detect e.g. distortions of the background star field?
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What is the maximum radius of an Einstein ring?

Is there an upper limit to how far out an Einstein ring can be visible? For black holes, is it a fixed multiple of their Schwarzschild radius?
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Where does the relativistic jet on Messier 87 come from?

I'm reading Wikipedia on Messier 87's jet The relativistic jet of matter emerging from the core [...] consists of matter ejected from a supermassive black hole. but later in the paragraph: Its base ...
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Are toroidal black holes hypothetically possible?

Since toroidal planet are hypothetically possible, albeit very unlikely to actually exist, can we extend this idea to black holes? Would these unstable bodies work atleast on paper?
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Are asymmetric black holes possible?

From an outside observer, if matter falls into a black holes from only one side, would the black hole's growth be asymmetric, and would it's gravity be non-isotropic?
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How did astronomers "measure a large (>40 degrees) misalignment between the black hole spin and the orbital spin" of MAXI J1820+70?

Gizmodo's Funky Black Hole Is Spinning Tilted says: A team of astronomers recently observed an askew black hole just 10,000 light-years from Earth. The black hole’s spin axis is out of alignment with ...
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At what distance does MOND Modified Newtonian Dynamics take effect?

At what distance does MOND Modified Newtonian Dynamics take effect? I understand MOND is described in relation to very slow accelerations, which is related to distance. It is mentioned it has an ...
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Pressure and chemical potential of quantum Schwarzschild black hole

Just as Stephen Hawking showed that even Schwarzschild black holes have a temperature, shouldn't it also have a pressure and chemical potential? Are there any analytical formulae of those as well as $$...
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Why do stellar-mass black holes fall to the centers of their galaxies? [duplicate]

This answer here says that black holes will "sink" to the centers of the galaxies they're in. How does this happen? It's not like there's a buoyant force in the vacuum of space. Shouldn't ...
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Why don’t black holes have an infinite rotational velocity? [duplicate]

We know that blackholes retain the properties of their progenitor, so if we think of the total angular momentum of a blackhole’s progenitor star now in an infinitesimal point (0 radius), should it’s ...
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How soon would an earth-mass black hole evaporate?

A raft of related questions: Is an Earth-mass black hole even possible? Assuming Hawking Radiation (HR) is a fact (has it been verified yet?), would HR cause an earth-mass black hole to evaporate ...
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If Planet 9 is a primordial black hole with a mass of 5 Earth, is it possible to detect it in a ground telescope? What should we seek in this case? [duplicate]

If planet 9 is not a planet but a black hole how can we find it? Can we see gravitational lense or infrared/gamma light?
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What is the relation between size (radius) of an astronomical object and the speed of oscillation of 'light' coming from it? (Strength/amplitude)?

From the year-end issue of New Scientist Magazine (Dec. 18-31,2021): Astronomy: 'Space Cow' explosion was probably a failed supernova' Page 10: 'They found that the strength of this radiation ...
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What is the reason for Hercules A to emit huge fountains of Plasma?

Hercules A, a supermassive-blackhole situated in the galaxy 3C 348, emits Plasma as far as 1.5 million light years away !! Although the cause is poorly understood, what could be the possible cause for ...
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2 votes
2 answers
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Would a planet orbiting black hole be detectable?

Usually missions like Kepler are finding exoplanets orbiting (the barycenter of systems related to...) stars at distances that are not common if compared with the Solar System. This finding (as I ...
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How is light unable to escape a black hole if photons are massless? [duplicate]

I understand light will follow the curved space that the BH is causing due to its mass. I also understand that mass attracts other mass but then photons are massless. So 0(photon) x m2 (the BH) is ...
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Is a black hole found in the centre of the low-surface-brightness and dark-matter-free galaxy AGC 114905

Per information found on Internet: AGC 114905 was discovered while observing the constellation Pisces with the VLA ground-based radio telescope. The galaxy is about 250 million light-years distant ...
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Have any HCSSs (supermassive black holes with a tight bunch of gravitationally bound stars) ever been detected?

This article from sciencealert states: Astronomers think these two galactic cores could merge into one larger black hole, sending huge gravitational waves rippling out across spacetime. But if there'...
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How did the Universe climb out of its own Big Bang black hole?

The Big Bang started as a singularity. That means small. All the matter in the universe was in a volume smaller than its own Schwarzchild radius. The universe was inside a black hole. At present, the ...
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Is there a comprehensive catalog of all known black holes? [duplicate]

Is there a comprehensive catalog of all known black holes? If "yes" - does it include the method of the black hole discovery and it's location in the Universe? Are black holes, detected only ...
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Has the Advection-Dominated Accretion Flows (ADAF) model been used to describe accretion flow around a rotating black hole?

I am studying Advection-Dominated Accretion Flows (ADAF) from the review paper Advection-Dominated Accretion around Black Holes. In section 2.1 of the paper, the authors provide the basic equations of ...
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Does general relativity imply that singularities cannot exist?

General relativity states that all matter in the universe is moving forward through spacetime at the speed of light. Objects that are stationary in space travel at c along the time axis, and objects ...
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What if hypothetically Ton 618 could have been a star

Assuming Ton 618, the largest ultra massive black hole wasn’t the result of feasting on near by matter but was hypothetically once a single star body. How large in terms of size would TON 618 have ...
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What does 's' or 'ds' or $ds^2$ mean in the Schwarzschild equation(s)? [closed]

And: These are from Wikipedia on Schwarzschild metric, Derivation of the Schwarzschild metric and the last is from Science Direct, Schwarzschild metric.
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The question regarding ZTF20acigmel space event detection

I have a question re аrXiv preprint article: https://arxiv.org/pdf/2110.05490.pdf It describes the detection of a space event, dubbed ZTF20acigmel, which was a massive explosion in a galaxy located ...
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How come a "failed supernova" is, well, "failed"?

I heard about this a while ago but recently came back to it: https://en.wikipedia.org/wiki/Failed_supernova which suggests that basically what this is is something where a star is so big and heavy ...
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