15 votes
Accepted

How can a brown dwarf be more massive than a star?

Yes, it has to do something with metallicity. Brown dwarf SDSS J0104+1535 $\to 0.086\rm\, M_\odot\to[Fe/H]=-2.4$ Red dwarf EBLM J0555-57Ab $\to 0.081\rm\, M_\odot\to [Fe/H]=-0.24$ There is an article ...
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  • 2,835
14 votes

Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?

Leconte et al. (2015) suggested that the presence of an atmosphere could prevent or at least slow tidal locking. The star should exert two separate torques: one on the atmosphere and one on the solid ...
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10 votes

Are Brown and Sub-Brown Dwarfs secretly more common than stars?

The answer to your first question is (now) fairly simple: No, brown dwarfs are not more common than red dwarfs. A crude approximation is that stars (which are indeed mostly red dwarfs) outnumber brown ...
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9 votes
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Is the mechanism of solar flares on red dwarfs and brown dwarfs the same as that on the Sun?

Yes, the basic mechanism is thought to be the same on red dwarfs and at least the hotter brown dwarfs, but the details can be different. As you say, magnetic reconnection in the corona is the ...
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  • 115k
9 votes
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Are red dwarfs really 30-100 times our Sun's density?

Red dwarfs, depending on your definition, can range from 2.5 to 150 times more dense than the Sun. What is the cause of this discrepancy? They give no calculations, so I can only guess. The article ...
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  • 308
8 votes
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Would a red dwarf star resemble our own Sun at sunset to an observer on a nearby planet?

Your question may ulitmately be about the physiology of the eye, which is off-topic here. The spectrum of the Sun seen low on the horizon is quite different to the spectrum of an M-type red dwarf. The ...
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  • 115k
7 votes

Are Brown and Sub-Brown Dwarfs secretly more common than stars?

This is an important question to ask about the initial mass function of objects in the Galaxy - and the final answer hasn't been cast as it is a matter of research. Yet, observational data (e.g. see ...
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7 votes
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How do we know that 2MASS J0523-1403 is a red dwarf?

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 ...
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  • 115k
7 votes
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Existence of planets larger than their host star?

The answer to the question depends on the exact definition of planet that is used. A possible example is the L dwarf 2M 0746+20 (2MASS J07464256+2000321) and its planet 2M 0746+20 b. The radius of ...
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  • 694
7 votes
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Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?

Yes: It has a companion planet or an excessively large moon, with the two bodies orbiting their common center of mass (much like the Earth and the Moon). They could be tidally-locked to each other, ...
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  • 102
6 votes
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How do I understand a brown dwarf with a M-type spectrum?

The spectral type of an object is almost entirely determined by the temperature of its photosphere. ie Saying something is type M3.5 is just a measure of its surface temperature. An M3.5 brown dwarf ...
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  • 115k
5 votes
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Will all of the gas in the universe be converted into red dwarf stars?

No. The reason is that gas recycling only recycles only about 40-50% of the gas in a sun-like star, leaving the rest as a white dwarf that slowly cools off. Heavier stars are even less effective in ...
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5 votes

Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?

The more likely case is actually a spin-orbit resonance that is not 1:1 but a half odd multiple, like the 3:2 case of our own Mercury. Having eccentricity in the orbit encourages this situation. I’...
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4 votes

Comparing orbits between a planet and Red Dwarf

earth like planet orbiting around a sun like star (365 days) red dwarf on an elliptical orbit around the star that passes close to the planet (1896.59 days, eccentricity 0.866) If we work in AU and ...
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4 votes
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Are there any hot jupiters orbiting red dwarfs?

I found one "hot Jupiter" in the Kepler data (Kepler 45b). The star is a M dwarf with an effective temperature of 3820K. The planet has an estimated mass of 160.5 M(Earth) and radius of 10.76 R(Earth)....
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4 votes
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Red dwarf variation in Luminosity

The creator seems to be referring to flare stars. Flares may be magnetic in origin, like various manifestations of the Sun's magnetic field. These flares can be quit luminous across the ...
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3 votes
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At what distance does Proxima Centauri become visible to the naked eye?

"Back of an envelope" calculation: Proxima Centauri has an apparent magnitude of about $11$. The faintest objects visible to the unaided eye have magnitudes about $6.5$. So we need to decrease ...
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  • 619
3 votes
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The colour of blue dwarf stars

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 ...
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3 votes

Existence of planets larger than their host star?

Beyond red dwarfs, another possibility is that of a planet orbiting a type B subdwarf star. Some features of such stars: Composed almost entirely of helium Thought to be formed through the merger ...
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3 votes
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What if a white dwarf is less massive than her partner?

If they are close enough to exchange mass, the Red dwarf will always lose mass to the white dwarf. That doesn't mean there won't be some exchange going back the other way, but the white dwarf will ...
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3 votes
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If the Earth circled a red dwarf/giant or a brown dwarf, would its sky still look blue?

If we take 1 atmosphere of optical depth to mean looking though the Earth's atmosphere at zenith, then the optical depth to scattering is small - probably of order 0.3 for blue light and much smaller (...
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3 votes

Are red dwarfs really 30-100 times our Sun's density?

This is a brief letter to Nature from 1946, containing no quantitative justification of the density estimate In 1946, whilst the radius of some of the nearest red dwarfs could be estimated from their ...
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  • 115k
3 votes

Are Brown and Sub-Brown Dwarfs secretly more common than stars?

According to the wiki article on sub-brown dwarfs, the lowest mass object that can form from collapse of gas cloud is about 1 Jupiter mass. Original source: Boss, Alan P.; Basri, Gibor; Kumar, Shiv S.;...
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2 votes
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Would the electron cyclotron-maser emission mechanism affect Proxima b's ability to retain an atmosphere?

This mechanism, being actively emitting in the radio-wavelengths, is certainly negligible for the overall atmospheric energetics at Proxima b. One can conclude this by taking the band luminosities ...
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2 votes
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Why is the SETI survey limited to only Red Dwarf Stars?

Sun-like yellow dwarf stars are generally thought to be the best places for intelligent life to develop, if only because 100% of known life is in orbit about a yellow dwarf. Larger, brighter stars ...
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2 votes

How do I understand a brown dwarf with a M-type spectrum?

There are a couple different tests you could use to determine whether the object is a brown dwarf of a red dwarf. You could try to use the lithium test to determine whether the object in question is ...
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  • 33.8k
2 votes

The tidal locking problem concerning Earth sized planets in habitable zone around Red Dwarfs

There is quite simple formula that will give you the tidal-locking half-time $$T = C\, \frac{a^6 R \mu}{ M_s M_p^2}$$ $a$ - semi-major axis, or simply the radius of the planet circular orbital ...
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