# Tag Info

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What concave lenses are used for is anti-matter astronomy: http://www.world-lecture-series.org/san-marino-2012-the-novel-mathematics-underlying-hadronic-mechanics-for-matter-and-antimatter This is not yet widely accepted in mainstream astronomy/astrophysics, but has been experimentally verified, see results: ...

0

A macroscopic body at over 900 km/s is a very unlikely event in the Solar system (may I skip explanations?), but an astronomic body “happy” enough to collide with a neutron star will certainly impact the surface at very high speed (values depend on mass of the star). BTW, relativistic collisions between neutron stars, or of a neutron star and a black hole, ...

0

Entropy and 2nd law as disorder is a massive misunderstanding (propagated by prestigious physicists non-the less). In fact on this issue there are various physics schools of thought (and especially those of the thermodynamic flavor) which set this whole discussion on a new footing. It is shown that (for example in the work of Nobel-laurate I Prigogine) how ...

4

A brief overview of stellar evolution can be depicted in the following image: (From here which says it is originally from an encyclopedia; click here for larger image). The heavier stars (top track) have very short life times (a few million years) because they run through hydrogen, helium, carbon+oxygen, ..., iron fusion in the core. Once a particular ...

4

You are neglecting two important facts. The first one is that stars, toward the end of their lives, return to the interstellar medium (ISM) a lot of their initial mass, but now enriched with heavy elements produced by nuclear reactions inside the stars themselves. In this way, younger stars which form from the ISM begin their life with a larger fraction ...

1

Gyrochronology is semi-empirical in the sense that there is some justification for the temporal dependence that you mention. There is a line of argument for the $t^{1/2}$ dependence and it can be found on pp7-8 of this pedagogical review by Jerome Bouvier. http://arxiv.org/pdf/1307.2891v1.pdf The basic idea is of a spherically symmetric, ionised wind that ...

2

Can't be done, yet. But don't expect 3d printing to stand still, it's only recently been born, wait till it starts walking, and running! My hope was that there could be a vacuum process that was usable in just enough vacuum to form a perfect mirror shape over a perfect mirror mold of some kind, then start the vapor deposition on the cheap, lightweight ...

1

It is difficult to keep track on these things, specially since quasars are also highly variable. Trying to answer the question of the post title, I found this example that sound pretty impressive: $7\times 10^{14}\,{\rm L_\odot}$, or $1.4\times 10^{41}$ W. The ESO press release refers to the kinetic luminosity, or the kinetic energy of the outflow per unit ...

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The highest resolution 3d printers I know of are around 1600dpi, which is a resolution of about 15$\mu m$. Telescope mirrors have to be smooth to fractions of a wavelength of light, so the resolution of current printers is nowhere near good enough. Whether 3D printers could one day be good enough is a different question, but given that the improvement in ...

2

Have a look at the Wikipedia article on Tests of General Relativity. The most recent measurement quoted there was by a group from the University of Texas. You can find a copy of the paper here. They measured a deflection of $1.66$ arcseconds $\pm 10\%$, compared to the prediction from General Relativity of $1.75$ arcseconds. Respond to comment: The ...

3

I will select quotes from the wiki article on structure formation, bold mine: The very early Universe In this stage, some mechanism, such as cosmic inflation, is responsible for establishing the initial conditions of the Universe: homogeneity, isotropy and flatness.3[6] Cosmic inflation also would have amplified minute quantum fluctuations ...

1

A recent paper suggests a mechanism to create totally metal stars. Some Stars are Totally Metal: A New Mechanism Driving Dust Across Star-Forming Clouds, and Consequences for Planets, Stars, and Galaxies http://arxiv.org/abs/1406.5509 Ordinary star formation produces planetary mass objects (sub-brown dwarfs), so perhaps this new mechanism would also do so. ...

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The plasma around Sgr A$^*$ is emitting in X-rays which indicates 10$^7$ K temperatures. Densities vary between 10$^6$ atoms/cm$^3$ and 10$^8$ atoms/cm$^3$, depending on which point along the accretion disk (pdf link)--possibly also depends on who you ask. I don't know that we can answer this question for many wavelengths as there can be a lot of stuff in ...

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