Questions tagged [accretion-discs]

Questions regarding disks of gas, dust, and plasma around a central object, such as a black hole, which takes in the matter.

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What does using these units (c=G=M=1) in MHD simulations mean?

I was reading some papers on numerical HD/MHD simulations of black hole accretion disks, and most of them scale their physical quantities to this form of units: c = G = M = 1. I know c = 1 and G = 1 ...
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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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Speeds in accretion disks

I know that in accretion disks, differential rotation means that inner parts move faster than outer parts. However, when angular momentum transport occurs (through viscosity, the magnetorotational ...
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Why is synchrotron radiation from relativistic electrons low in energy?

Why do populations of relativistic (high energy) electrons emitting synchrotron radiation emit at mostly radio wavelengths? The fact that they are high energy makes me think they would emit high ...
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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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12 votes
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How do rocky objects between 1cm and 1m accrete to form planetesimals?

I am having a hard time gaining an intuitive understanding of some of the middle stages of planetary formation from a protoplanetary accretion disk. I understand that microscopic dust particles may ...
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5 votes
3 answers
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Could a black hole's accretion disk be bright through natural means?

This question is based on this description of the Cormoran Supermassive Black Hole in the Orion Arm's website: Surrounding this event horizon is an (apparently artificial) accretion disk about 4AU in ...
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Has gain in mass from accretion onto a black hole been observed?

Have we observed a black hole directly gain mass via accretion? That is, have we observed the black hole to have mass $m_1$ at time $t_1$ and then observed its mass to be $m_2 > m_1$ at a later ...
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2 votes
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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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What does "synchrotron emission from relativistic electrons in equipartition with a ∼1.5 mG magnetic field" mean?

I've heard of the equipartition theorem in the context of thermodynamics. But I don't understand how either "synchrotron emission" or "relativistic electrons" can be in "...
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How much matter was ejected when the Solar System formed?

Assuming the accretion disk model for the formation of the Solar System, the most important problem, according to wikipedia, is "how the material, which is accreted by the protostar, loses its ...
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Why are accreting objects portrayed with a white flash at the point where the gas stream from the star enters the accretion disk?

When I see images of accreting objects, the gas from the donor has a white flash where it meets the accretion disk, like in the image below. Why does this happen if it is true, and why is it there?
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Why are relativistic jets perpendicular to the accretion disk?

From looking at many images (artist's rendering and computer-generated) at black holes, I've noticed that the relativistic jets are always perpendicular to the accretion disk. Is this always true, and ...
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3 votes
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How will they know when to start taking the picture of the black hole at the center of the Milky Way?

@csm's answer to Why not take a picture of a closer black hole? points out that it's necessary for the supermassive black hole at the center of a galaxy to be actively feeding for it to generate a ...
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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 is angular momentum transferred between a neutron star and its accretion disk?

Accreting neutron stars can either gain or loose angular momentum via interaction with their accretion disks. This leads to either spin-up or spin-down. Which of the two is the case, depends on the ...
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How do accretion disks around black holes evaporate via winds?

I'm curious as to how accretion disks around black holes evaporate. I've heard winds play a crucial role in this. But what winds specifically and how do they form? Is it a stellar wind of sorts? If so ...
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How does gas in accretion disks of supermassive black holes create orbital torques on smaller black holes within the disks causing them to migrate?

This answer to What enhances the capture and merge rates of pairs of small black holes orbiting around supermassive black holes? links to Migration Traps in Disks Around Supermassive Black Holes which ...
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Why would the merger of spinning black holes within the accretion disk of a supermassive black hole cause them to "shoot straight up" out of the disk?

I just tried to read the new New York Times article Two Black Holes Colliding Not Enough? Make It Three which links to the new 25-June-2020 Physical Review Letter Graham et al. Candidate ...
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What enhances the capture and merge rates of pairs of small black holes orbiting around supermassive black holes?

I just tried to read the new New York Times article Two Black Holes Colliding Not Enough? Make It Three which links to the new 25-June-2020 Physical Review Letter Graham et al. Candidate ...
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Is Beta Lyrae still thought to be losing mass in a spiral outflow?

In the famous 1960 painting by Chesley Bonestell, Beta Lyrae is depicted with a glowing spiral trail of matter emanating from the binary stars. I'm wondering if that's still thought to be a ...
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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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Can white dwarfs have accretion discs too?

Neutron stars and black holes can have discs of accreted matter for they have an extremely high gravitational pull. While white dwarfs don't have such high gravity theirs is of course also extremely ...
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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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How are microlensing events used to constrain the size of innermost stable circular orbits around spinning black holes?

The third paragraph of the introduction to the ArXiv preprint Constraining Quasar Relativistic Reflection Regions and Spins with Microlensing says: Quasar microlensing has significantly improved our ...
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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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Why didn't all the iron and heavier elements find their way to the center of the accretion disc in the early solar system?

I guess that's pretty much it. I just heard that that a meteor fragment was found to be solid iron and it just seems inexplicable that it was floating around.
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2 votes
2 answers
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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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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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Mini disk of a blackhole meaning

What is meant by the "mini disk" of a blackhole? Is it the same as accretion disk? If not, whats the difference? Eg: In the abstract of this paper https://arxiv.org/abs/1806.05697 it is mentioned "...
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What is the exact meaning of vicinity of Black hole or a disk? the same as inside?

What is the exact meaning of vicinity of Blackhole or a disk? Is this the same as inside the horizon for black holes? If so, why people don't say inside of BH, simply. What is the difference? I use ...
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How did they make a video of the center of the galaxy, and what is it exactly that's flashing there?

The ESA video ESOcast 173: First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole includes a clip of images of stars at the center of our galaxy orbiting around SgrA*, a ...
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7 votes
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If space was n>3 dimensional, would clouds of particles still turn into 2D disks due to gravity?

I don't fully understand why clouds of particles which turn into galaxies and solar systems usually result in an (approximately) 2D shape, but whatever. Would they still result in an almost 2D shape ...
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15 votes
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What is it exactly about these flares of infrared light from Sgr A* that "confirms" it is a supermassive black hole?

CNET.com's SCI-TECH Scientists confirm a 'supermassive black hole' at the heart of our galaxy It's "mind-boggling", they say. This links to Astronomy.com's Scientists finally confirm the Milky Way ...
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4 votes
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Astrophysical Jet Size?

I am wondering about what is the estimated size of astrophysical jet that shoots out from a black hole, I don’t know if it is determined by the size of a black hole. What would classify a black hole ...
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What defines the plane of an accretion disk around a black hole?

The question Do we know at which angle the Event Horizon Telescope will look at the accretion disk of Sagittarius A*? about just how close to edge-on we would be viewing any accretion disk around the ...
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14 votes
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Quasar mass and accretion rates

This page on Wikipedia -- Quasars mentions that the "The largest known [quasar] is estimated to consume matter equivalent to 600 Earths per minute". However, there is no citation for this comment. How ...
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What stabilizes rings or accretion disks?

We think, more or less, that our Moon was formed from an accretion disk caused by a Mars-sized impactor. Cool. Tidal forces can break apart a moon, causing rings. Ashes to ashes, dust to dust: the ...
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Can matter fly directly into a black hole and avoid the accretion disc?

From what my non-scientifically-trained mind understands, matter typically enters a black hole via getting caught up in the accretion disc going faster and closer to the black hole until it passes the ...
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18 votes
4 answers
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Did the earth form outside the solar system?

Why isn't it possible that the earth formed outside the solar system and got attracted later by the Sun? I just need arguments to defeat this hypothesis.
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1 vote
1 answer
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Accretion discs emitting jets [duplicate]

When there are accretion discs jets of particles or radiations will be emitted in the direction parallel to the rotational axis. My beginner level astronomy textbook just says that it is due to ...
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3 votes
1 answer
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Spherical Accretion (Bondi Model)

I have a question. I studied Bondi's model for spherical accretion. I know the assumptions made in the model are big and that they are rarely representative of what happens in astrophysics. What I ...
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Minimum Mass Solar Nebulae Scaling Factors

I'm attempting to build a MMSN, I've been trying for about... a week to get an intuition on the scaling factors for calculating the mass of the disks, I'm not entirely sure how to think about it. I ...
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0 votes
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Do massive OB stars accrete mass the same way as the black holes they turn into do?

It is often said, in spite of sci fi often having illustrated the opposite, that stellar mass black holes do not gravitationally attract material in their environment into themselves anymore than a ...
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3 votes
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Luminosity of black hole accretion disc

The luminosity of a black hole accretion disc gaining mass at a rate $\mathrm{d}M\over \mathrm{d}t$ can be estimated as $${1\over 12}{\mathrm{d}M\over \mathrm{d}t}c^2$$ That is a substantial ...
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2 votes
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Linear extent of an accretion disk

I have a homework assignment question on accretions discs (essentially an estimation of the number of electron scatterings, but this is just for background). There are a few parameters, one of them ...
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1 vote
1 answer
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Do the terrestrial planets form later than gas giants in our solar system?

Sorry I forgot where this statements come from, but I also remember the reason behind it is due to young Jupiter moves inwards and destroys the original super earth in inner solar system, and the ...
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6 votes
2 answers
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When a neutron star accretes matter, will its mass increase?

When a nova gets matter, the outcome is that it may lose more matter because of eruptions. Only some kind of nova's masses can increase stably. A white dwarf may become a supernova after it exceeds ...
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1 vote
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What is the mass limit in a stellar accretion disc?

I became curious about the maximum mass in a star's accretion disc while watching an episode of Star Trek involving a Dyson Sphere. I wondered if some maximum amount of stellar material would limit ...
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3 votes
0 answers
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Angular momentum in planetary disk formation

Reading about the formation of planetary disks, one of the major problems, it seems like, is the evacuation of angular momentum. Aparently planets can't form with the amount o angular momentum the ...
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