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Questions tagged [accretion]

Questions regarding the process of a massive body gaining mass from objects around it.

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How well are planetary formation models (e.g., determining $\mathrm{\dot{M}_{planet}}$) understood in 2024?

I know that planets can form through accretion, bulging up from $0$ to their final mass $\mathrm{M_{planet}}$ at $\mathrm{M}(t_f)$. I know that when studying Planetary formation and migration theories,...
nuwe's user avatar
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4 votes
1 answer
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Degenerate object accretion - what happens after it becomes a PMO?

Degenerate objects such as neutron stars and white dwarfs can be accreted from by other objects. As the degenerate object loses mass, it could pass through different mass ranges which govern the ...
WarpPrime's user avatar
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10 votes
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What is the mechanism through which mass is converted to thermal energy in the accretion disc of a black hole?

In the book The Cosmic Perspective, it is stated that as matter is falling into a supermassive black hole, up to $40\%$ of its mass are converted to thermal energy, making the accretion of matter ...
Vercassivelaunos's user avatar
20 votes
2 answers
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Is there enough matter orbiting the sun to make a second sun?

I read somewhere a long time ago that there is enough matter in our solar system in the form of rocks and dust to create another sun.Is this correct? Was our solar system trying to create a 2 star ...
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Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow?

Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow? I mean is it mandatory for a jet to be emitted from an accretion disk? If so, then why? ...
SCh's user avatar
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8 votes
1 answer
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What is it like to see a brown dwarf turn into a star?

Brown dwarfs/failed stars can actually become stars, if they exceed a mass limit of about 80 Jupiter masses. This is when the internal pressure and temperature at the core become high enough to ...
Alastor's user avatar
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7 votes
2 answers
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Can a brown dwarf accrete enough mass from red giant to become a star?

Let's assume a brown dwarf is on orbit around a main sequence star. Than the star becomes a red giant. Let's assume the brown dwarf has "the right" orbit and can syphon matter from the red ...
Heopps's user avatar
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How to get started with computational astrophysics? [closed]

I am a graduate student working on high energy astrophysics, in particular, accretion onto neutron stars and my research is mostly theoretical. However, with the recent advances in observational ...
Richard's user avatar
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1 vote
1 answer
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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 ...
theta's user avatar
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1 vote
0 answers
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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 ...
Richard's user avatar
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6 votes
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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 ...
Daddy Kropotkin's user avatar
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Accretion disk formation

Why a mass transfer in a binary star system, from the less dense star to the denser star forms an accretion disk? Why the material does not fall directly to the denserstar?
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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. ...
slowerthanstopped's user avatar
1 vote
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What is the effect of extinction in the accretion disk for black hole mass determination?

I've created a basic model of the accretion disk (AD) by summing up blackbodies following the temperature profile of the AD according to Shakura & Sunyaev (1973) (extensively used in the ...
Lorz.Astro's user avatar
1 vote
1 answer
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What about the magnetic field strength inside of an old accreting neutron star?

As the magnetic field strength outside an old accreting neutron star is thought to be small (about $10^8-10^{10}$ Gauss), what about it inside the star? Because of the superconductivity and ...
Chen's user avatar
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2 votes
2 answers
378 views

Why doesn't smashing larger and larger bodies incrementally into a rocky planet create a star?

Let's start with a stationary Earth. If we smash a few Mercury-sized objects into the Earth, the Earth begins to accrete mass. Repeat this step with larger and larger objects, until we start impacting ...
WarpPrime's user avatar
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5 votes
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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 ...
SpaceCore's user avatar
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4 votes
1 answer
248 views

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 ...
user30007's user avatar
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3 votes
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What is the "radiation sound speed" inside an accretion column?

I was trying to read "A New Two-fluid Radiation-hydrodynamical Model for X-Ray Pulsar Accretion Columns" and its follow-up paper both by West et al. and came across a quantity called "radiation sound ...
SpaceCore's user avatar
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6 votes
3 answers
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Where do rocks come from?

Consider a loose pile of rocks in an early solar system, say a tiny asteroid. As it accretes more and more material, the pressure at its center eventually becomes great enough to collapse the gaps ...
Camille Goudeseune's user avatar
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 ...
RenatoRenatoRenato's user avatar
9 votes
2 answers
414 views

Why do black holes choke?

I read that a black hole can sometime "choke" on a star: "...the disrupted stellar matter was generating so much radiation that it pushed back on the infall. The black hole was choking on the ...
user6760's user avatar
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2 votes
2 answers
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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 ...
MichaelJRoberts's user avatar
1 vote
1 answer
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accretion discs in h/lmxbs

High mass x-ray binaries necessarily accrete via wind, no disc accretion? What makes the difference between a hmxb and a lmxb? In what kind of circumstances does an accretion disc form? How does it ...
questionhang's user avatar
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