# Tag Info

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Rob jeffies gave the results for what the core looks like. But for completeness that hydrogen shell envelope is big, very big. Its of order 1000 times the radius of the Sun. Or in other words if it replaced the Sun it would extend out to about Jupiter.

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Pre- supernova models often characterise the compactness of the core using a "compactness parameter" defined as $$\upsilon = \frac{(M/M_{\odot})}{R(M)/1000\ {\rm km}},$$ where $M$ is usually chosen to be $2.5M_{\odot}$ and $R(M)$ is the radius within which $M$ is contained. Pre supernova models by Farmer et al. (2016) show that the central $2.5M_{\odot}$ ...

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Im looking for this as well, have you found more information about this topic? In this picture fusion looks like to take place in a very small core but no precise numbers are given https://supernova.eso.org/exhibition/images/0406_3_DUM/ In this article the proportion star/core is given for red supergiant https://sites.ualberta.ca/~pogosyan/teaching/...

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There is no lower limit, and as you say, all stars are somewhat variable. However catalogues of variable stars exist, and they can record a wide range of levels of variability. For example, the general catalogue of variable stars lists stars like Alpha Triangulum, with a variability of 0.01 magnitudes. Ultimately a variable star is a star which has had ...

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Certainly sunspots (or "starspots") won't count, as they are statistically random and thus unpredictable, as well as causing a very small delta in total output. edit: I stand corrected. There's a Wikipedia page (thanks, HDE) which describes several classes of aperiodic stars. These stars do continue to undergo significant variation for at least many ...

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With the Gaia Data Release 2, you can plot an HR diagram with a few million stars. From the Gaia website : The data can be accessed in the search tab, where you can specify the columns you want to display (phot_bp_mean_mag and phot_rp_mean_mag). There is a button at the bottom to export the results to a file on your computer. You can then plot one of the ...

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In Equation (16) of the paper you link to, $z$ is the observed redshift. In the first paragraph of section 2.2 The heart of the method is to use a measured redshift, z, to infer a velocity, v(z)

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Based on this article, as stars age, they spin more slowly. The age of stars can therefore be estimated by measuring the stars' rotation : fast spinning stars are young while slow spinning stars are old.

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I don't know about stars in general, but for giant stars, the following histogram shows the age distribution of those in our Galaxy based on their location in the Galaxy. This means that most stars are between 7 and 8 billion years old.

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TL;DR: the main sequence lifespan of the sun can be increased by a factor of 12.2. Perhaps the most complete astrophysical analysis of stellar engineering for extending Earth habitability is Martin Beech's book Rejuvenating the Sun and Avoiding Other Global Catastrophes (2008). In order to maintain the biosphere the sun's interior need to be mixed (in ...

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LORRI will be used in 4x4 mode, which yields 4-arcsec pixels. The error in positions is unlikely to be better than 1%, or 40 mas, about 200x larger than Gaia's error. NH has a baseline ~20x larger, but this means it still misses Gaia by ~10x. The date was selected for New Moon to help Earth observers find the two targets. There is no Earth analogue for ...

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There is a candidate ring system around the L-type brown dwarf G 196-3 B. According to Zakhozhay et al. (2017), the brown dwarf has a mass of ~15 Jupiters and a temperature of ~1870 K. They model it as being surrounded by a warm, narrow debris disc located close to the brown dwarf (~1280 K at a distance of ~0.12–0.20 solar radii). ...

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Usernumber's explanation of the light and dark regions is correct, but there is more detail to be added about granulation on other stars. Granulation is expected on other stars with surface convection zones, but the properties and timescales of the granulation can be quite different. On the Sun, the granules appear and disappear in timescales of 10-30 ...

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I'll add to @usernumber's answer some graphics. Unfortunately we can't yet "has YouTubes" for some reason so I'll just add the links. There are two videos of the Sun linked in Phil Plait's Bad Astronomy article DKIST first light high-resolution video of solar granules DKIST First light video of solar granulation (wide angle). Here are the same kind of ...

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The dark lines are colder areas at the edge of the convection cells, where the cooled down plasma sinks towards the inside of the Sun. The yellow parts are where the plasma rises to the surface. Each yellow spot (which is actually the size of a country) is called a granule, and this web-like appearance is called granulation. In the outer part of the Sun (...

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While a whole slew of signals will arrive once the supernova actually occurs, from neutrinos to light of all different energies and wavelengths, the outward, visual appearance of the star will not give any surefire clues that a supernova is imminent. But the nuclear reactions powering the star do change over time, and at just 640 light-years away, Betelgeuse’...

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Even though it arised for historical reasons outlined in the other answers, the distinction between metals and non-metals as defined by astronomers does continue to make sense today. Metals are formed in stars and supernovas, whereas non-metals preexist stars. Therefore, the distinction is relevant when considering nucleosynthesis.

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One reason to prefer the space between the temperature and luminosity classes is that the hypergiant luminosity class is "0", which could be confused with a subtype. Usually this appears as part of a range with luminosity class "Ia" as opposed to on its own, but this range is often written as "0-Ia". Something like "G5 0-Ia" is more comprehensible than "G50-...

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Normally, you would write G2V (with no spaces), as separating each part of the classification would cause some ambiguity. Basically, any star's classification would be written as 'Temperature class'+'Digit'+'Star type.'

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