16
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 ...
- 2,939
15
votes
Accepted
Is there more dark matter than we previously thought?
Probably nothing changes
Several reasons for this:
The study actually asserts (last paragraph of main text) that:
The IMF variation also calls for an extensive revision of star formation rates and ...
- 4,851
15
votes
Accepted
Are any Population III stars red dwarfs?
Yes, in principle, but while we have indeed found some extremely low-metallicity stars, we have yet to discover zero-metallicity stars. Moreover, accretion of metal-rich gas over billions of years may ...
- 39.6k
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 ...
- 37.4k
12
votes
Is Barnard's star an M4 red dwarf or an M0? Why is it called an M4.0V?
It's M4V, not M0V.
In principle, spectral classes can be further subdivided, particularly in the M class, because there are significant differences between an M4 and an M5 spectrum for instance.
...
- 162k
11
votes
Accepted
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 ...
- 18.4k
11
votes
Red dwarfs and red giants
According to Laughlin et al. (1997), (still the canonical work) it is only stars below about 0.25 solar masses that fail to become red giants.
Stars between 0.25 and about 0.5 solar masses will become ...
- 162k
9
votes
Accepted
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 ...
- 564
9
votes
Accepted
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 ...
- 744
8
votes
Accepted
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, ...
- 112
8
votes
Accepted
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 ...
- 162k
8
votes
Is there more dark matter than we previously thought?
Barely, because the estimates of dark matter are not sensitive to the IMF, they use (a) the dynamics of objects in galaxies to estimate the total mass of that galaxy, (b) observations of kinematics in ...
- 162k
8
votes
Why do red dwarf (M-type) stars give off such violent flares and CMEs, out of proportion to their size and temperature?
Magnetic activity in the form of magnetically powered flares, hot X-ray emitting coronal, UV-bright chromospheres and starspots is driven by an interior stellar dynamo. Whilst the details of how this ...
- 162k
7
votes
Accepted
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 ...
- 162k
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 ...
- 21.4k
7
votes
Red dwarfs and red giants
There is an issue with regard to the statement that red dwarfs do not become red giants. This is perhaps an oversimplification. A better statement is that small red dwarfs do not become red giants in ...
- 36.3k
6
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’...
- 1,018
6
votes
Accepted
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 ...
- 162k
6
votes
Accepted
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 ...
- 15.7k
6
votes
Do red dwarf stars get dimmer over time, the opposite of most other main sequence stars?
This image from Red Dwarfs and the End of the Main Sequence shows the evolution of a $0.1\,M_\odot$ star:
The x-axis is the effective temperature of the star (cooler on the right as usual), and the y-...
- 129k
6
votes
Why do red dwarf (M-type) stars give off such violent flares and CMEs, out of proportion to their size and temperature?
You would think that M-type dwarfs would be among the more magnetically stable stars due to their low temperature and mass, but they aren't.
This is because such low-mass red dwarf stars are ...
- 1,144
5
votes
How would you calculate the "day" on a planet orbiting a red dwarf that is a companion to a larger star?
While the situation is not exactly the same, the complexity is similar to calculating when the Moon is visible from a point on Earth.
Just as the Earth rotates once a day (or 23hr56 min), and the moon ...
- 129k
4
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 ...
- 162k
4
votes
Accepted
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 ...
- 495
4
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 ...
- 4,185
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 ...
- 30.7k
3
votes
Accepted
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 ...
- 24.2k
Only top scored, non community-wiki answers of a minimum length are eligible