Questions tagged [black-hole]

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

49 questions with no upvoted or accepted answers
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7
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142 views

Why would a black hole have a disk, but not emit x-rays?

There's a recent paper in Nature about LB-1, a B-class star orbiting a massive black hole. I don't understand how these two parts of the paper can be reconciled. On page 2, the authors argue that the ...
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123 views

Has the Penrose process ever been linked to an observed phenomenon in some way?

This answer to What defines the plane of an accretion disk around a black hole? mentions the Penrose process as a potential mechanism that could change the axis of the orbital angular momentum of an ...
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Is there work underway to push the long baseline capabilities of the Event Horizon Telescope to sub-millimeter wavelengths?

The Max Planck Institute for Radio Astronomy's press release Something is Lurking in the Heart of Quasar 3C 279; First Event Horizon Telescope Images of a Black-Hole Powered Jet shows a stunning ...
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Is the discovery of a “mass gap” black hole by this tiny telescope just plain luck/serendipity or could it be the first of many similar discoveries?

The Kilodegree Extremely Little Telescope is a pair of modest lenses with high quality medium format CCDs attached sitting on oversized mounts in Arizona and Sutherland. These very modest instruments ...
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156 views

Can primordial black holes be found orbiting other stars?

A recent study suggests a that a primordial black hole may be orbiting the sun at and that they can be common near other star systems. What measurements and equipment can perhaps find BH's near ...
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1answer
257 views

Why did the Event Horizon Telescope take so long to take a photo of a black hole?

The Event Horizon Telescope is in the news now because they are about to release the first ever picture of a black hole. They have been working on this since 2006. Why did it take 13 years to produce ...
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44 views

What scales and types of EM and gravitational radiation do we expect to be given off by a black hole, in the final stages of evaporation?

In theory, black holes of all sizes eventually evaporate, due to quantum processes close to the event horizon that result in net emissions that appear to come from the black hole (but actually ...
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37 views

Astronomical resources helpful for creating an animation in the browser of the movements of an astronomical object in the sky?

Background I would like to create a website that shows an animation of the path of Sagittarius A* (or any other object in space) during one day for a specific location. So that the user can see where ...
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61 views

Charged black holes selective eaters

We have a charged black hole which is negatively charged. For this simple case the black hole is not rotating. If a negatively charged particle approaches the singularity the electromagnetic repulsion ...
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57 views

Why does the outside edge of a Kerr black hole ergosphere rotate at the same speed as the inner edge?

Reading through the Wikipedia on a Kerr black hole ergosphere, and this nice question on the maximal spin rate of a black hole leads me to ask: why does the outer edge of the ergosphere rotate at the ...
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140 views

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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48 views

Does General Relativity predict anything about the creating of a singularity, once enough matter collapses inward to form an event horizon?

Ignoring quantum gravity, which we don't know much about, current theory (GR) states that an event horizon forms when there is enough matter/energy density to create it, and logically, a singularity I ...
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Can mass loss via accretion occur on stellar remnants?

We know that normal stars can lose mass to a binary companion. But can this happen to neutron stars and white dwarfs? Let's say a stellar black hole is being orbited by a white dwarf or neutron star. ...
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48 views

What fractions of matter are retained and displaced by quasars?

Following on from a query concerning quasar mass, what fraction of matter is ejected compared to matter that is lost to the BH? Is there a graph that describes the fractions of the mass of quasars ...
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294 views

How does the size of a naked black hole effect its photon sphere?

What effect does the size of a black hole have on the size or density of the photon sphere and it's proximity to the horizon? For example: A person is in space looking at 2 black holes, one of them ...
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Can we resolve the centers of Milky way's satellite galaxies now?

Two dwarf satellite galaxies of our galaxy have large $\frac{\text{diameter}}{\text{distance}}$ values. And one of them, Canis Major Dwarf, is 8kpc away which is the same with our distance to the ...
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Could we detect a globular cluster consisting entirely of black holes?

A paper recently came out in Nature simulating the evolution of the $\sim10^4M_{\odot}$ globular cluster Palomar 4 (Gieles et al. 2021, arXiv link). The authors argue that in ~1 billion years, a ...
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59 views

Would a possible accretion disk around a primordial black hole 500 au from the Sun be visible in present telescopes?

If the hypothetical two-inch black hole 500 au from the Sun had an accretion disk, might current telescopes detect it already or do we have to wait till the Vera Rubin Observatory starts work?
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Can a Thorne-Żytkow object be the progenitor of a modern quasi-star?

I was reading some Wikipedia articles about astronomy, and came across an interesting line: The neutron star may also accrete sufficient material to collapse into a black hole. Now, here is my ...
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What methodology should be used to choose the correct model for origin of QPOs in X-ray astronomy?

In X-ray astronomy, quasi periodic oscillations (QPOs) are routinely shown by black hole and neutron star X-ray binary systems in their X-ray flux. Despite being strong and easily measurable signals, ...
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How does hawking radiation work without virtual particles?

How does hawking radiation work without the existence for virtual particles? I read that certain quantum fields are distorted when a black hole forms on top of them. But what fields specifically? If ...
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93 views

How String Theory calculates the Entropy of the Black Hole in a Background dependent way?

How does string theory get an agreement to the Hawking-Bekenstein equations to calculate the quantum entropy of a black hole in a background dependent way? Is there any sort of area parameter in ...
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If Planet Nine is a primordial black hole could it explain 'Oumuamua and Borisov's orbits without them being interstellar?

There has been an increasing amount of interest in the possibility of primordial black holes and that Planet Nine may be one itself. Planet Nine is a potential explanation for the orbital ...
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46 views

Why are pseudo-Newtonian potentials used in studies of accretion processes around black holes?

In accretion processes around black holes, pseudo-Newtonian potentials are defined for the the black hole geometry. For examples, the potentials defined by Paczynski-Wiita and Artemova et al. for ...
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Is there a way to calculate how much damage black hole merger shockwaves inflict on nearby objects?

Black hole mergers lose respective rotational energy during a merger. I understand that the energy 'emitted' is scattered as gravitational 'energy' that can henceforth be detected by gravitational ...
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Can we determine where the north and south magnetic poles are on stars and black holes?

The question is related to this about Are there collected data about the direction of rotation of black holes and the direction of the magnetic field?. Perhaps it is observable for pulsars?
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How well conserved is etendue in extreme gravitational lensing scenarios?

This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description: Light from the background galaxy circles a ...
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Can the other side of the observable universe be seen as a black hole?

When looking at the objects near the horizon of the observable universe, the objects seem to emit radiation that is red-shifted. Time seems to advance at a slower rate than our own and at the horizon ...
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44 views

Understanding various conditions where a star and a black hole meet and there is no tidal disruption; what all can we infer from this diagram?

Can an entire star pass through the event horizon of a black hole unharmed? is a one sentence HNQ with an amazing (to me at least) answer: for supermassive black holes larger than roughly 100 million ...
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1answer
172 views

How does Hawking Radiation work exactly?

I know that a particle and anti particle, virtual particles, spawn at the edge of an event horizon, and one particle falls into the black hole, and the other goes out, but how does the other know how ...
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59 views

Can massive objects pull photons into existence?

When a photon tries to leave a black hole, it is redshifted until the wave length is infinite and the photon disappears(?). Could this also happen the other way round, that a (non existent) photon ...
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Math for the “universe in a black hole” hypothesis?

There are various pop-science article entitled Are we living in a Black Hole? or Did A Black Hole Give Birth To Our Universe? which say things like There’s a lot to like about the idea that there’s a ...
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What is the relation between between hardness ratio(HR) and spectral state of a X-ray binary star system?

When reading about hardness ratio, it shows that depending on the hardness ratio spectral states of a binary star can be divided into soft, hard states. So how the HR value changes with respect to the ...
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88 views

What is the Schwarzschild radius actually?

I am currently writing a detailed essay about black holes, the history of their discovery and their characteristics and I can't find the appropriate literature online and in my local libraries (I even ...
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1answer
68 views

Primordial black holes microlensing

Could the movement of a PBH found in the outer solar system by microlensing be totally unpredictable and impossible to track after it was first detected?
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62 views

Does the spin rate of a black hole correspond to a physical feature?

If the mass and orbital period for two neutron stars is known before collapse to a black hole and the rate of spin is known after collapse, 100 revolutions per second for instance, that will correlate ...
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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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122 views

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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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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Does the Canis Major Dwarf Galaxy have a black hole at its centre?

I am just wondering: is there a potential galactic centre out there that's very close to us? I know that CMDG is irregular, but can it still contain a black hole at the centre?
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The black hole binary that was detected by advanced LIGO - how do such hypergiant binaries form?

With today's announcement of the historic detection of gravitational waves from the merger of 36 solar mass and 29 solar mass black holes 1.3 billion light years away, one can not help but wonder how ...
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1answer
141 views

Why does gravity make time go slower and warp light?

I know that objects with lots of gravity are capable of warping light or slowing time (an example being a black hole). I also know this is because of the theory of relativity, but I need someone to ...
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How can firewalls stay put on the event horizon?

Firewalls in black holes were introduced in relation with the information paradox. In Wikipedia we can read: A black hole firewall is a hypothetical phenomenon where an observer falling into a black ...
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What does it mean that a black hole has a magnetic field?

Black holes have a magnetic field around them. What does this mean for the interior of the holes? That a net electric charge is "flowing in one direction?" Or at least a net current was ...
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Do the orbits of 14 TNOs even need an explanation (a planet mass) or is it just for historical reasons (how they formed)?

From Uranus' orbit we concluded there must be another planet beyond Uranus, eventually discovered and named Neptune. The same happened when Pluto was about to be discovered (though on false premises). ...
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Could all spiral-galaxies with black holes at their centers be connected via the BH themselves or Einstein-Rosen-Bridges?

If it's true that almost every spiral-galaxy has a black hole at its center, then I have this question. Could all these galaxies be connected via their black holes, or their Einstein-Rosen-Bridges?
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How do dark stars form?

I'm not referring to a star made of dark matter or a Newtonian dark star. I'm talking about a star powered by dark matter annihilation. I imagine it would form close to the centers of galaxies where ...
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Is it possible that it actually takes an infinite amount of time to reach the apparent horizon of a black hole?

I know a black hole can absorb matter and maybe also release Hawking radiation. I think that according to the Gullstrand–Painlevé coordinates, space is flowing and the apparent horizon is the region ...
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Can Quantum tunneling be possible within Blackhole ? And if so, could that be the source of Dark Energy?

Quantum tunneling starts happening when there are empty energy states available for the electrons to occupy and the energy barrier is of the order of the wavefunction of the electrons. Could there be ...