# Tag Info

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TL; DR Somewhere between now and a few hundred billion years time. (For a co-moving volume) Now read on. If stellar remnants are included, then the answer is very far in the future indeed, if and when the constituents of baryons begin to decay. So let's assume that "stars" means those things that are undergoing nuclear fusion reactions to power their ...

20

If there is a way to violate a law of nature, it will become a law of nature as soon as it is discovered, studied and formalized into a scientific theory. Therefore, many new discoveries in science do violate (then current) laws of nature, but will not do so for very long. Often there are all sorts of medals and prizes involved too.

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Universality of physics As far as we know, laws of physics seem invariant both across space and time. It's not absolutely certain and taken for granted, there's lots of research probing to try and verify if perhaps something is slightly different far away or long ago, but to our best current knowledge the laws of physics work exactly the same in all faraway ...

12

TLDR; Its a diagram showing all the physics and modeling choices that go into different models (the colored boxes in the middle) to compute an SED. Longer answer: First a SED is a spectral energy distribution, i.e how the amount of light varies as a function of wavelength. These kind of plots help understand to understand the underlying physics of an object. ...

10

The scale factor of the universe depends on the matter and energy density in a way that depends on which component is dominant. This is discussed in the question How does the Hubble parameter change with the age of the universe? on the Physics Stack Exchange, and from that I have taken this graph showing how the scale factor changes with time for our ...

10

Van-der-Waals forces and gravitation are the main answer. The main property keeping together bodies smaller than a few $100 {\rm km}$ are their constituents surface forces between the grains (van-der-Waals) and chemical/ molecular bonding within the grains themselves. It's the same mechanic which makes the dust and grease in your flat stick to surfaces and ...

10

To understand the history of the figure in question it is important to understand some of the context. In the run up to the operation of advanced LIGO, it was widely expected that the first detections would come in the form of relatively weak signals, whose presence in the data could only be established by comparing with theoretical templates through matched ...

7

No. That's because we believe the laws of physics to be the same everywhere (this itself is a consequence of the law of conservation of momentum, via Noether's theorem). Therefore, if you can't violate the laws of physics as we know them on Earth, you can't violate them elsewhere, too.

6

Whether convection exists depends on whether the interior radiative temperature gradient reaches the adiabatic temperature gradient. The interior radiative temperature gradient is proportional to the opacity and the outward energy flux, and inversely proportional to $T^4$. As the star evolves on the main sequence, the central temperature goes up and the ...

6

In general, you can't. If obtaining spectra in regions where there is expected to be a spatially varying background then you either need to do long-slit spectroscopy so that you have a good measurement of the ISM contribution either side of your source, or you do integral field spectroscopy with the same idea. The problem is that the line strengths for the ...

6

SED fitting SED fitting is the practice of inferring physical properties of a stellar population (a galaxy, a cluster...) from measures of the Spectral Energy Distribution. The spectrum of a stellar population is extremely information rich. It can be used to infer age, redshift, metallicity, present and past star formation rate, total stellar, dust and gas ...

5

An asteroid resting on Earth would be a mountain. Or, for smaller asteroids, a pile of gravel. Mountains are limited in altitude by the strength of stone to resist compression: a too tall mountain would sink down as the base crumbled and spread out. The limit on Earth is about 10 km. Besides the strength issue mountains are also floating ("isostasy"...

4

Analytic models have been applied to various phases of the evolution, though it would be impossible to apply a single model to all phases because the physics changes so much. Also, a star will often have very different physics going on in various different parts of the star, so analytic models sometimes have to treat different parts separately and then ...

4

Why would precession affect the motion of the other planets? First things first: That's an unreferenced portion of a wikipedia article. That said, a perfectly spherical body acts exactly like a point mass in Newtonian mechanics. A non-spherical body does not. The Earth's equatorial bulge has a significant effect on satellites in low Earth orbit. Sun ...

4

This issue is a bit complex, and at its core revolves around the claim of a Copenhagen group led by Andrew Jackson that LIGO data was not handled correctly, a mislabeled plot, and some small (but since resolved) controversy regarding the transparency of LIGO science. When LIGO published their initial findings, they included a plot that was, indeed, adjusted ...

3

EdS universe represents a matter-dominated universe. Since the universe evolving towards lambda dominated and recently it was matter dominated, its a good approximation to use the EdS model to calculate the age of the universe.

3

Well, it's possible that physics as we know them are somewhat different elsewhere, or on different scales (both microscopic and macroscopic). So if we manipulate our environs in particularly extreme ways, as with the large colliders or extreme lasers, or if we inspect very large structures, we may observe phenomena not predicted by our current laws of ...

3

Convert the 3D luminosity distribution to mass using a bunch of mass particles. Well, you probably could do that, but I suspect it would be inaccurate and extremely time-consuming. Most Schwarzschild modeling approaches parameterize the 3D luminosity-density distribution using functions from which the gravitational potential can be relatively easily ...

3

The enhancement of a cross-section due to gravitational focusing is given by $$\sigma_{\rm eff} = \pi a_J^2 \left(1 + \frac{2GM_{\odot}}{a_J\ v^2}\right),$$ where $a_J$ is the semi-major axis of Jupiter's orbit (assumed circular), $v$ is the relative velocity (at infinity) and I have ignored the mass of Jupiter. Thus, using $v=30$ km/s (as specified in ...

3

The Lyman-Werner background (LWB) is the part of the "meta-galactic" background radiation consisting of photons that are able to photo-dissociate molecular hydrogen ($H_\mathrm{2}$), but not ionize atomic hydrogen (HI). These photons are in ultraviolet, with energies ranging from $11.2\,\mathrm{eV}$ to $13.6\,\mathrm{eV}$, originating mainly from hot, ...

2

Initial research proved to be wrong as intuition does not match up with expectations. Anyway, the paper referenced by the OP seems to sum up the answer to the question pretty well: In this explanation, the dark areas of our map represent thicker clouds that obscure deeper, hotter parts of the atmosphere and present a higher-altitude (...

2

This simulation (video link) has been made to show what a black hole might look like seen from different angles. From APOD : If the black hole was surrounded by a swirling disk of glowing and accreting gas, then the great gravity of the black hole would deflect light emitted by the disk to make it look very unusual. [...] Surrounding the central black hole ...

2

You question reminded me of a tool I first encountered in the 80’s (I know right!) called “data thief”. Back when Mac applications had a four letter “creator code” this one had the code “DIEF” (which is the Dutch word for “thief”). I appears to be around still - and as it doesn’t rely on a browser it may well still work (I haven’t tried in years though). ...

2

Aerosol physics is actually an old topic - yet still a very vibrant one. One main factor on the extinction (which sums up scattering and absorption) other than the distance (which is about constant when looking at a a particular zenith distance) is the wavelength $\lambda$ you look at compared to the typical aerosol particle radius $r$ as its ratio affects ...

2

I just became curious enough to search a few keyphrases. This article talks about hydrogen molecules acting as energy "sink" in the sunspots - much like water phase changes on Earth create climate features. The heat capacity, mass density, adiabatic properties of the molecular hydrogen are pretty much different from the atomic one and these are ...

2

The Earth's orbital speed around the Sun is about 30 km/s. So we can calculate the intersection of two spheres offset by 30 km. Suppose we put the first sphere at the origin [0,0,0], and the second sphere at [30,0,0]. That is, the x-axis is aligned with the orbital velocity vector. Then, from Wolfram, the intersection of the spheres is a curve lying ...

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I am an undergraduate in Physics, and I have an opportunity to work with a some of my seniors to learn Computational Fluid Dynamics (CFD) and Magnetohydrodynamics (MHD). Congrats! I would like to choose my first individual project in order to learn about how these techniques are used in Astrophysics. The answer to your question depends on what you mean ...

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Computational Fluid Dynamics and Magnetohydrodynamics are very important in understanding the interior of stars, star formation, the interstellar medium, accretion discs around stars,... So to answer your first question, I would say this is a great opportunity and it would be very beneficial to learn about it through a hands-on project with more experienced ...

1

The way disk-integrated and disk-resolved is used in your cited paper is nothing special, just indicating optical resolving power in relation to the image of the object of interest: With a disk-integrated signal they mean a single value as measured over the whole disk (of an image a planet makes - or whatever is imaged as a disk). When they talk about disk-...

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Diclaimer: This is not (yet) an answer! To attract answers, I decided to start an answer draft which can be expanded by others. Cylindrical coordinates Every point in our cylindrical coordinate system is defined by a tuple $(r,\varphi,z)$ where $r$ is the distance from the rotational axis. We also define $Z$ as the height of our solid of revolution, i.e. \$0 \...

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