19 votes

Does a star fuse helium to beryllium on the main sequence?

Does a star fuse helium to beryllium on the main sequence? Stars don't fuse helium to beryllium except as a very, very short intermediate step toward carbon. Helium-helium fusion to form beryllium is ...
  • 28.7k
12 votes
Accepted

Increase in Luminosity of the star

The luminosity mass relation is inexact. The luminosity also depends on the composition of the star, particularly in and around the nuclear burning regions. The composition changes during the main ...
  • 120k
11 votes
Accepted

Does a star fuse helium to beryllium on the main sequence?

What defines the main sequence? Main sequence stars are characterized by hydrogen fusion in their cores, either through the proton-proton chain (for lower-mass stars) or the CNO cycle (for stars more ...
  • 34.2k
10 votes
Accepted

Is there a relation between mass, radius, and luminosity in deuterium-burning brown dwarfs?

Yes, there are monotonic relationships between mass and luminosity and radius on the "deuterium burning main sequence". Deuterium "burning" begins when the core temperature exceeds just over $10^6$ K....
  • 120k
9 votes
Accepted

How does a star's rotation affect a star on the main sequence?

This is a well-studied problem. The effect of rotation on the structure of a low-ish mass star (like the Sun) is summarised by Eggenberger (2013). Such stars are never observed to rotate so fast that ...
  • 120k
9 votes
Accepted

Is "Main Sequence" a temporal sequence?

No, the Main Sequence is more like a starting line. Most stars spend a long time on one point of it (10 billion years for the sun) while they fuse hydrogen into helium. Then they wander off it. In ...
  • 461
8 votes

Is "Main Sequence" a temporal sequence?

Is this in any sense a temporal sequence? Not really. At least not in the sense of a star sliding along the main sequence. That doesn't happen. Instead, a star remains more or less parked at one spot ...
  • 28.7k
8 votes

Is "Main Sequence" a temporal sequence?

The main sequence is mostly a plateau that a star reaches after it is fully formed but before it begins to run low on hydrogen to fuel normal fusion reactions. And yes, the sequence is mostly an ...
7 votes
Accepted

On a Hertzsprung-Russell diagram, why is the main-sequence line squiggly?

Here is another plot of a Hertzsprung Russell diagram (luminosity versus temperature), but this time based on theoretical models. (The plot is from D. Prialnik 2000, An Introduction to the theory of ...
  • 120k
6 votes
Accepted

Why does the convective core in an intermediate- to high-mass star shrink?

Whether convection exists depends on whether the interior radiative temperature gradient reaches the adiabatic temperature gradient. The interior radiative temperature gradient is proportional to ...
  • 120k
6 votes
Accepted

What will be the temperature on Earth when Sun finishes its main sequence?

The difference is that your analysis is assuming that the albedo stays fixed, so the surface temperature simply scales like luminosity to the 1/4 power. The Wiki entry is including feedback from the ...
  • 5,180
6 votes
Accepted

Is the conversion from proto-star to main sequence an event or a process?

Astronomers distinguish a prototstar from a star based on whether the object is visible. A protostar is hidden by the gas cloud that surrounds it. Protostars aren't visible. At some point in their ...
  • 28.7k
6 votes
Accepted

What is the largest hydrogen-burning star?

I assume by largest, you mean largest radius. Well it won't be VV Cep B since this is merely a B-type main sequence star. O-type main sequence stars are known and these have both larger masses and ...
  • 120k
5 votes
Accepted

Description of Henyey tracks on wikipedia incorrect?

The wording provides a contrast with the Hayashi track phase that immediately precedes it, where the luminosity decreases by orders of magnitude with little change in effective temperature. You are ...
  • 120k
5 votes
Accepted

Why are main sequence stars more massive than the Sun less dense? e.g. Vega, Spica etc

Main sequence stars are defined by being hot enough in the core to fuse hydrogen, so their core is at least about 10 million K, and can get up to 20 million K for the more massive ones (because they ...
  • 5,180
5 votes
Accepted

Why is the main sequence often called 'zero age' main sequence?

The zero age main sequence (ZAMS) is the theoretical locus of points in the Hertzsprung-Russell diagram where the luminosities of young stars (at a range of masses) are mostly supplied by the nuclear ...
  • 120k
4 votes

Which would be safer: removing hydrogen or adding hydrogen to our sun?

My kneejerk reaction is that your only option is to remove a chunk of mass from the outer part of the Sun. The Sun will respond (on a Kelvin-Helmholtz timescale), by contracting and becoming less ...
  • 120k
4 votes

Does the luminosity of a star on its main sequence increase or remain approximately constant?

The luminosity of a star remains approximately constant during its time on the main sequence. There is a slight increase over time, which is, as you guessed, related to the changing composition of the ...
  • 34.2k
4 votes
Accepted

What would happen to the Sun's evolution if it collided with another yellow dwarf?

If the Sun collided with another star about the same mass, then its mass would be slightly less than 2 solar masses, as some material would be ejected away from the merger. This would result in an A-...
3 votes

Is the turn-off point of the main sequence the same as the terminal-age main sequence?

TL;DR: Turn Off point (TO) means the location of the "knee" in the HRD of clusters of stars. TAMS is an imaginary line in the HRD that is defined by the location of stars of different mass at the end ...
3 votes

Why is the main sequence often called 'zero age' main sequence?

This answer may be a bit speculative but still I thought to give it try. A.S.Eddington The Internal Constitution of the Stars (Cambridge University Press, 1926) has probably been one of the most ...
3 votes

Why is the main sequence often called 'zero age' main sequence?

The term "zero age Main sequence" is there only because during main-sequence evolution, hydrogen is turned to helium, changing the stellar structure a little (electrons are eaten up, light escapes ...
  • 5,180
3 votes
Accepted

Is it possible for a star to return in the main sequence?

The evolution of a star is irreversible process, so strictly speaking, it is impossible to return the star back to its earlier phase (it is impossible to collect all energy it has radiated to space ...
3 votes

Are older main-sequence stars found in or near molecular clouds?

Stars do not stay where they are born. They orbit in our galaxy and their orbits are subject to relative perturbing forces caused by galactic tides and encounters with spiral density waves and other ...
  • 120k
2 votes

Accretion of in-falling material for a young main sequence star

At the end of the protostar phase a vigorous outflow from the star develops called the T-Tauri Wind and this could cut off accretion. Eventually, it develops into a normal star and the strong wind ...
  • 2,857
2 votes

What's an order-of-magnitude main sequence star look like?

To get an order of magnitude estimate you can just use the total mass $M$ and luminosity $L$ of the star and an assumption of your fusion process. Main sequence stars fuse Hydrogen in to Helium ...
  • 1,458
2 votes

How can pre-main sequence stars radiate more energy than main-sequence stars?

The luminosity of a PMS star is provided by the rate of change of gravitational potential energy as it contracts. Since PMS stars contract along Hayashi tracks at almost constant effective temperature,...
  • 120k
2 votes

Why do post main sequence stars enter the red giants branch?

If your question is why the star starts moving up the red giant branch, it's in essence because of the behaviour of the surface opacity and the development of a substantial convective envelope in ...
  • 2,692
2 votes
Accepted

How long does it take a star to transition from main sequence to red giant?

It takes a star like the Sun about a billion years to go from the end of core hydrogen burning to the beginning of helium core burning. One might not call that entire phase a red giant phase, however,...
  • 5,180
2 votes

How can I estimate how long will a main sequence star stay on the main sequence given its temperature?

The website on Main sequence stars fromr the Austalian national telescope facility lists star mass, temperature and life span: Mass/MSun Luminosity/LSun T=Effective Temperature/K Radius/RSun t=Main ...
  • 93.9k

Only top scored, non community-wiki answers of a minimum length are eligible