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Breaking the phrase down: Dwarf star - a term I will never understand - is used to describe relatively small, dim stars. Unfortunately, this encompasses most main-sequence stars, which are indeed dwarfs compared to large giants and supergiants. Ultra-cool, as called2voyage already discussed, means that the star has an effective temperatures of less than ...


8

According to Spectroscopic Properties of Ultra-cool Dwarfs and Brown Dwarf by J.D. Kirkpatrick, the working definition of ultra-cool dwarf is: dwarfs having classifications of M7 or later. That is referring to the stellar classification system which categorizes stars by their spectral characteristics. Class M stars have a surface temperature less than ...


7

A 1 solar mass, Earth sized black dwarf would have a surface gravity of about 360 000 g which probably rules out manned exploration by anything we would normally think of as human. For similar reasons, mining would be quite challenging. Another obstacle is that the Universe is not old enough to have produced any black dwarves yet. The oldest white dwarves ...


7

The brown dwarf "limit" is about $0.072 M_{\odot}$ at solar metallicity (e.g. Chabrier et al. 2000) and is composition dependent. It gets a little higher in metal-poor gas and a little lower in metal-rich gas. $0.064 \pm 0.012 M_\odot$ (the third significant figure is superfluous) is within one error bar of that limit, which in itself is only a 68% ...


6

Collisional broadening - which includes van der Waals and Stark broadening - is more important in the higher gravity, higher pressure/density atmospheres of dwarf stars (a factor of 100-1000 higher for dwarfs vs giants of the same photospheric temperature). These collisional effects effectively "truncate" radiative emission and absorption processes,...


5

Certainly a red-dwarf star can have enough energy for a planet around it to be in the goldilocks zone. There are some difficulties with red-dwarf stars and Earth like planets. The planet would need to be very close to the star and as a result, tidally locked. The orbital period would be quite short, so there would be no seasons and one side of the ...


5

First. In about 6 billion years the Sun will become much larger than it is now, maybe a factor of 20. It will be a red giant. Then a little while later it will get really big, as large as the earth's orbit and perhaps the Earth will be engulfed. Second. Only after this does the Sun lose about half of its mass and the remainder is exposed as a small, hot, ...


3

I'm not exactly sure what you're asking, cause you touch on a few related points. The reason planets around red-dwarf stars are thought to be tidally locked is because the tidal force is comparatively much greater for the habitable zone. Take, for example, a star with half the mass of our sun. It would have, roughly speaking, 1/16th the solar output, so ...


3

I emailed the authors of the paper, asking whether blue dwarf stars could "become hot enough to pass the thresholds for Type B or Type O" and one of them replied: "We use the term 'blue' to mean 'bluer', so that when stars become blue, they get hotter than their usual main sequence temperatures. ... The point of the paper is that smaller stars get ...


3

So far, opinion is divided, as evidence has not been found to prove either way. Back in 2015, a study published in Nature, and linked via the Verge, here suggested that no, brown dwarfs do not exhibit star-like behaviours, but are in fact much closer to planets (due to them being below critical mass for hydrogen fusion in their cores) All planets that have ...


2

Looking at the diagram as a whole, the bottom line seems to be the type of object that a star in that category will evolve into. So a large star that is variable due to mass loss will explode in a type II SN and evolve to either a Black Hole, or a Neutron star (which may become variable as a pulsar but ultimately evolves to a non variable NS. Looking down ...


2

The Sun is white, in the sense that you can hold up a white piece of paper to it and see no color, it's what our eyes have adapted to. And it is a dwarf, in the sense that it is a main-sequence star, and all such stars are called dwarfs. But it is definitely not a white dwarf, that's a much smaller (size of Earth) and much older star. The names are not ...


1

There's a bit of confusion in the nomenclature here. This is very important: The nomenclature for labeling largish objects in space was developed before scientists knew anything about fusion. Stars on the main sequence fuse hydrogen to form helium. Except for extremely massive stars, every star on the main sequence is a so-called dwarf star. These main ...


1

Let's take a look at the star and the planet's characteristics first. We have the star TRAPPIST-1: $M = 0.082 M_{\odot}$ $R = 0.117 R_{\odot}$ The planets are all roughly in the scale of $0.7 R_{\oplus}$ to $1.2 R_{\oplus}$ with their semi-major axes of: b: $1.66 \times 10^6 \; \mathrm{km}$ c: $2.88 \times 10^6 \; \mathrm{km}$ d: $3.14 \times 10^6 \; \...


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