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We have reasonably good measurements of the mass of Sagittarius A*, thanks to measurements of the movements of stars like S0-2 over several decades. It's been well-established that the mass of the central object is $M\approx4\times10^6M_{\odot}$; this alone is fairly good evidence for a supermassive black hole, and we can constrain the size of the object ...

23

The chance happenstance that Earth happened to be floating along and got captured is minuscule. How did Earth wind up floating through space? There's no established mechanism for terrestrial planets to form on their own. As far as we know, they need a host star to form around. So if our Sun captured Earth, it must've formed around another Star, got ejected ...

16

I think the Earth's orbit is by far the strongest argument you have that the Earth formed around the Sun. The orbit is nearly circular and almost in the Sun's equatorial plane, similar to the other planets. These facts are naturally accounted for if the Earth formed from material that coagulated in the Sun's primordial disc, where circularisation and ...

13

Question: How are these images obtained? Later in the video the narrator says they took the images using ESO's VLT. 03:40 [Narrator] 14.​ Making these measurements pushed the power of ESO’s Very Large Telescope to the limits. (Source: ESO transscript) Over the whole observation period multiple telescopes and imaging instruments were used. Early ...

13

The process of differentiation is how metals like iron and nickel can become separated from less dense substances. It generally occurs in large, partly solid bodies in the early solar system, whose interiors are melted either via accretion energy, radioactivity or some combination of the two. A solid iron meteor is likely a fragment of a differentiated ...

12

Tricky to say for sure, but I would imagine it comes about from measurements of the luminosity and inference of the black hole mass in such systems. The most extreme objects radiate at the Eddington luminosity, where gravitational forces on matter falling into the black hole are balanced by radiation pressure from the heated material closer in. If ...

8

It is actually the other way around: First a massive accretion disc can form, through which material looses angular momentum and accretes onto the star radially, hence being angular momentum poor. However, during the initial free-fall phase, before the disc forms, infalling material can be 'rejected' at the star, either via high pressure gradients or ...

8

This is indeed a tricky problem, and the accretion of pebbles to form planetesimals is a big question in planetary science. You are right to say that small particles can stick together through electrostatic forces if collisions are gentle enough. But as particles increase in size, bouncing and fragmentation seem to present a barrier to growth. This is ...

7

Let me see if I can try answering both parts of your question. The key is a combination of two things: 1) Most of the binary BHs in an accretion disk will have their binary orbits in the same plane as the accretion disk, so that "perpendicular to the binary plane" = "perpendicular to the accretion disk"; 2) The most effective form of ...

7

Unfortunately, the answer is "No", because accretion rates are far too low -- and our ability to measure black hole masses is far too uncertain -- for this to be visible in reasonable times. Given our current ability to measure black hole masses, you'd typically have to wait millions or tens of millions of years to see any accretion-related changes....

6

Let me give an answer based on my intuitive understanding of the thing... Initial conditions The initial accretion disk movement is defined by the objects falling into it, the black hole's mass and its spin of course. If you take the situation where a single star falls on a quiet black-hole, the accretion will appear along the orbit of the infalling ...

6

It just so happens that this problem has been rigorously analyzed. Max Tegmark wrote an interesting paper on it which can be gotten from the arXiv. It is not super-technical, so I recommend you look at it. Basically, with more than three space dimensions there are no stable orbits. Particles either disperse to infinity or collapse to a point (presumably a ...

6

The picture is of the central region of M87, taken at a wavelength where the gas is "optically thin". The ring of bright light is pretty much exactly where it is expected to be for the synchrotron radiation emitted by the hot gas to have been gravitationally lensed by a black hole with the same mass as deduced previously from the motion of stars close to ...

6

As I understand the quote, the "artificial" thing about your accretion disk is not that it is bright, but that it doesn't emit X rays. In real life, SMBH accretion disks are usually exceptionally bright. The disk itself has a strong emission in the UV, called UV bump, that can easily exceed the emission of the whole host galaxy. Above and below the ...

5

There's two different effects here, and they're both related to viscuous forces in the accreting matter. First, if the infalling matter has some nonzero angular momentum vector $\mathbf{L}$, then consider a plane perpendicular to this vector. Due to its conservation, we can't get rid of rotation along this plane, but the component of angular momentum ...

5

It depends on the distance from the central body. This gives the temperature $T$ at a given point as a function of the distance from that point to the center ($R$): $$T(R)=\left[\frac{3GM \dot{M}}{8 \pi \sigma R^3} \left(1-\sqrt{\frac{R_{\text{inner}}}{R}} \right) \right]^{\frac{1}{4}}$$ where $G$, $\pi$, and $\sigma$ are the familiar constants, $M$ is the ...

5

The radiation being detected in this case is mostly synchroton radiation, caused by energetic electrons spiralling around magnetic field line, rather than thermal radiation, but it comes from the same place (the disk). The actual evidence for light bending is, I believe the dark area in the middle, which is several times larger than the actual event horizon ...

5

When the stream of gas falls towards the disk it gains a significant fraction of the orbital kinetic energy (after all, it is falling from the top of the Roche lobe) which means that it is moving fast and then slows down sharply when it interacts with the disk. This produces a hot spot that in theory could reach $10^8$ K but in practice "merely" is ...

4

Three times the Schwarzschild radius corresponds to the closest stable circular orbit around a black hole. The general idea is that as matters moves in towards the black hole it gets stuck in an accretion disc where angular momentum has to be moved outwards in order to allow the matter to move inwards. The generic mechanism is some sort of viscosity, which ...

4

It would be really difficult for the Earth to end up in a nearly circular orbit if it came from outside the solar system. Effectively falling from infinity, it would have a hyperbolic orbit and make one swerve around the Sun and depart back into the blackness of interstellar space. What mechanism could get rid of precisely enough energy to keep the Earth ...

4

In your analogy: A satellite stays in orbit because it has angular momentum. This always balances the force of gravity, thus when being in the satellite (or in the ISS) it seems as if you're weightless, because force balance. This is very important to understand, because it is the reason that in space all orbital motions can -in principle- go on forever. ...

4

I have not the qualification to answer the question in its whole but the question is interesting (I worked on Be Stars which are episodically surrounded by an decretion disk and which rotates at nearly critical velocities. The phenomenon in Be stars is different from accreting stars. The only consequences of subcritical velocity is a flattened envelope and ...

4

I would think that the same reason that a gas disk enhances the growth of planetesimals. Drag from the disk enforces circular, co-planar orbits, which in turn means that objects that get close to each other have small relative velocities. Edit: So what is thought to be going on is a little bit more complex than the simple answer above. The density of massive ...

4

Not really my area, but this question is probably related to the planetary migration in circumstellar disks. In this case, the migration is caused by gravitational interactions between the planet and the gas in the disk. There are two explanations for this effect Impulse approximation: consider a parcel of gas in the corrotating frame. If the gas is close ...

4

We can think of the magnetic field lines as part of its host gas in the jet, in the sense that when the gas moves, the magnetic lines of force must move with it - and vice versa. Magnetic field lines passing through an accretion disc are thus forced to rotate with the disc. The particles of ionised gas above and below the disc are then urged to rotate with ...

3

One example is that of the core of a Thorne–Żytkow object, or TŻO. It consists of a high-metallicity M class red giant or supergiant with a neutron star at its core. Generally, TŻOs form when a neutron star collides with a suitable red giant/supergiant. The neutron star settles into the center of the other star. Eventually, the main source of energy for the ...

3

Many, if not all, stars will, in their birth phase, have an accretion disk, or circumstellar disk, around them, formed of the material from which the star forms. This disk dissipates in a few million years, both due to the material accreting onto the star, due to material being blown away by radiation pressure, possibly assisted by dust grains, and due to ...

3

Occam's razor defeats the hypothesis. There are no astronomical anomalies about earth's obit or position that require the complication of earth's insertion from beyond the solar system. Unless some difficulties in known fact are brought forth requiring such a hypothesis as their simplest solution, then the idea may simply be rejected as unnecessary. The ...

3

The accretion disc is formed by material in orbital motion against a central body, which can be a star. The size, mass and other characteristics are usually determined by the central object, in this case the star. In general, the protoplanetary accretion discs are the largest ones (with the largest mass) and as the age on the central star increases, the ...

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