5
votes
2answers
196 views

How to explain the existence of heavier elements in Population I stars and in Population II stars contain lighter one

Recently I read Astrophysics Notes where I found a statement that young stars are classified as Population I stars and relatively older one as Population II stars. Population I stars contain ...
0
votes
1answer
31 views

Multiple planets orbiting a star

One way of detecting exoplanets orbiting around a star is the Radial velocity method. Can this be used to detect multiple planets? Wouldn't the star orbit the center of mass of the whole system with ...
8
votes
2answers
101 views

What is the Sun's core made of?

The obvious answer is hydrogen and helium plasma but the nuclear fusion can also create heavier elements. Are these heavier elements a significant portion of the core? Do the heavier elements "sink" ...
12
votes
1answer
505 views

What is the percentage of stars that are massive enough to end their lives in a supernova?

I have been searching for the percentage of stars that are massive enough to end their lives as a supernova but couldn't get any result. As far as I know, a star has to be at least 8 times more ...
19
votes
4answers
2k views

Can there be Electron and/or Proton Stars?

What happens to all of the electrons and protons in the material of a neutron star? Could there ever be an electron star or a proton star?
0
votes
1answer
39 views

Quick question on derivation of mass of star

How do I show that for a binary star system, if one star has mass $M_s$, speed $V_s$, period $P$, the mass of the other star is given by: $$M_P^3 \approx \frac{V_s^3}{2\pi G} PM_s^2$$ I showed it ...
5
votes
1answer
55 views

Lifetime of a horizontal branch star

I'm trying to determine what the lifetime of a star on the horizontal branch of the Hertzsprung-Russell diagram would be. Some websites say $10^8$ while others said $10^7,$ so I don't know which one ...
0
votes
1answer
55 views

Quick question on parallax and parsec

I know that 1 parsec (pc) is the distance of star at which 1 AU subtends 1 arcsecond. so $1 pc = \frac{1 AU}{1"}$ Now, if two stars in a binary with a separation of 3" and have a trigonometric ...
0
votes
3answers
90 views

Is the solar energy Infinite?

Is the solar energy coming from the sun infinite and will continue to be radiated to our earth forever? (discarding any outer factors) what's the sun's fuel?
5
votes
1answer
95 views

Upper Mass Limit of Quark Stars

While there is no confirmation that quark stars exist, is there any theoretical limit analogous to (but different from) the Tolman–Oppenheimer–Volkoff limit for neutron stars? In other words, what is ...
11
votes
3answers
2k views

If I were standing on the surface of the sun, how far could I see?

Assuming it would be possible to handle the intense heat... Is the surface even? If not, would average surface elevation be an appropriate definition of "surface"?Does the sun have an atmosphere that ...
3
votes
2answers
83 views

When a star turns into a red giant what stops its core contracting

I recently asked this question When do stars become red giants? and am now wondering when the star's core is contracting after it has fused $H$ to $He$ what force stops the contraction just before it ...
2
votes
2answers
78 views

When do stars become red giants?

I am a bit confused when do stars become red giants? Is it just after they have finished core H burning and the core contracts creating high temperatures which result in core He burning to occur which ...
1
vote
1answer
80 views

Inward Pressure of Gravity

We are looking at White Dwarfs in Quantum and specifically how they are stabilized between gravitation pressure inwards balanced by the Fermi pressure due to electrons. To start the problem off ...
1
vote
3answers
90 views

State of the Stars

What's the state of stars? I'm not pretty sure whether the stars are stationary or rotating. For instance, if they are not rotating what makes them to be stable?
2
votes
1answer
112 views

Why does a star beyond a certain mass limit (Chandrasekhar limit) only become a black hole?

Why does a star beyond a certain mass limit (Chandrasekhar limit) only become a black hole? A star is first made of hydrogen, it undergoes nuclear fussion reaction combining into helium and ...
14
votes
5answers
3k views

Why does a star collapse under its own gravity when the gravity at its centre is zero?

The gravity at the centre of a star is zero as in the case of any uniform solid sphere with some mass. When a massive star dies, why does it give rise to a black hole at it's centre? I know how to ...
2
votes
1answer
57 views

Implications of the Jeans mass

The minimum mass for the spontaneous collapse of a gas cloud is the Jeans mass. For low temperatures and high densities, this jeans mass is greater than the mass of a typical star. What are the ...
4
votes
2answers
184 views

What is a simple mathematical model of a star?

I had a discussion at work regarding a recent fusion experiment in China that resulted in temperatures five times hotter than the Sun. Someone mentioned that no one can know the temperature of the ...
4
votes
1answer
142 views

Is a Betelgeuse supernova able to neutralise earth's nuclear arsenal?

According to an article on newscientist.com, a neutrino beam could neutralise nuclear bombs by inducing a slow meltdown of the nuclear fuel. The neutrino generator would need to be more than a ...
0
votes
1answer
67 views

What is the intrinsic colour of the star? [closed]

Hey I have this question and I am wrestling with it all day and I am completely lost. The V magnitude of a star is 15.1, B-V =1.6, and absolute magnitude Mv= 1.3 The extinction in the direction of ...
2
votes
1answer
87 views

Relation of fraction of binary stars with spectral class (mass)

What is relation of fraction of binary stars with spectral class (mass)? For example, how many binary stars are among O,B,A,F,G,K,M stars separately?
7
votes
2answers
173 views

What causes the dimensions of a star increase when its hydrogen fuel is exhausted?

What causes the dimensions of a star increase when its hydrogen fuel is exhausted? For example, the Sun is expected to increase its radius 250 times. What causes this if its temperature is expected to ...
3
votes
1answer
51 views

Stellar Activity Cycle versus Metallicity

Our Sun exhibits sunspot max/mins on about a 11 year period. It's a G2 spectral class on the HR Diagram. We know that some stars exhibit "starspot" cycles of various intensities and periods. These ...
3
votes
1answer
55 views

Are initial mass functions summable?

I tried to sum up two weight ranges of the IMF which wouldn't not work so my question is, if I'm doing something wrong. Let's say my weight ranges are $\left[X M_{\mbox{sun}}, Y ...
7
votes
3answers
217 views

Can a planet form before the parent star ignites?

I'm unable to find an answer to my questions via my searches. This questions pertains to the timeline of a star system creation. My question: During the creation of a star system, can satellite ...
1
vote
1answer
54 views

Why isn't all of the dust in a nebula used in the formation of a star?

I was watching a show on discovery and according to it, in a nebula the dust and gases slowly come together and as the gravity increases and the pressure rises in the core the gases fuse together and ...
-1
votes
1answer
135 views

How does physicists calculate the gravitational self collapsing force of a star?

The nuclear fusion taking place inside the stars opposes its gravitational self collapsing force. But, how does physicists calculate it? I just know the classical gravitational theory and not a bit of ...
21
votes
3answers
1k views

Are neutrino stars theoretically possible?

Since neutrinos have a small mass and are affected by gravity, wouldn't it be theoretically possible to have such a large quantity of them so close to each other, that they would form a kind of a ...
4
votes
2answers
482 views

Why can't Iron fusion occur in stars?

It is said that iron fusion is endothermic and star can't sustain this kind of fusion (not until it goes supernova). However star is constantly releasing energy from fusion of elements like Hydrogen ...
7
votes
2answers
231 views

What are the demographics of stars visible to the naked eye?

Of the stars that can be seen with the naked eye, what are the distributions of each type? For example, how many are main sequence? how many are Super Red giants/white dwarfs/neutron stars...etc. ...
3
votes
1answer
127 views

How much faster is the fusion we make on earth compared to the fusion that happens in the sun?

I have come across many websites that states that the proton-proton fusion which is the dominant type of fusion that powers the suns, is extremely slow and that is why the sun is still burning to that ...
5
votes
1answer
174 views

Oldest population 1 star system?

While reading Stanislaw Lem's essays on advanced civilizations, I had a question: When did the earliest generation of population 1 star systems form? How much older could they reasonably be than our ...
4
votes
1answer
983 views

When does a planet become a star?

How big can a gas giant become before it's considered a star? How does the theoretical maximum compare the observed maximum?
5
votes
1answer
219 views

Red Giant branch and Asymptotic Giant branch

What's the difference between the RGB and the AGB? I can't seem to find an clear distinction anywhere. Thanks.
2
votes
2answers
246 views

Dark age of universe when all fusion process ceases?

Some say we live in the golden age of the universe because there exits countless number of stars that shines in the dark universe. As the supply of gas for star formation is steadily being exhausted, ...
7
votes
2answers
132 views

Speed of birth of a star

A star forms when enough material gets close enough. But how fast does the star start to shine? Is it gradually heating up (similar to an oven) slowly shining more and more? Or is it more like an ...
7
votes
1answer
203 views

Do any stars exist apart from galaxies?

Do any stars exist apart from galaxies? Do "maverick" stars exist?
1
vote
2answers
138 views

starlight flux on earth

I want to calculate if it is possible to photograph a subject lit only by starlight. I found one website claiming that a starlit scene is lv = -15 (daylight is lv 15, or 2^31 times brighter), but he ...
6
votes
2answers
193 views

How do interstellar hydrogen atoms form stars?

I would like to learn the basics about how interstellar matter contracts into stars under the influence of gravity. Some of my questions: Let's assume an ideal and infinite large cloud of equally ...
3
votes
1answer
742 views

How does a star ignite?

I remember reading that X-Rays are generated by 'braking' electrons in a Coolidge tube. Is it fundamentally a matter that the extreme gravity immediately before a star ignites is so strong that it ...
1
vote
1answer
77 views

What would be the effect of an excess of up quarks on stellar formation?

Suppose you had 80% up quarks, and only 20% down quarks. How would this affect stellar formation?
0
votes
1answer
51 views

Conversion of a star

I need to know what would happen to a star that has size 2 times the solar mass. I guess it would either be a neutron or red giant. Is that right?
1
vote
1answer
65 views

Initial separation of neutron star/black hole binaries?

How would I go about finding the distribution of initial separations (i.e. the lengths between the centres of mass) of stars that make up binary systems. I am interested in neutron stars and stellar ...
2
votes
2answers
98 views

How accurate are our calculations about distant stars keeping in mind their enormous distances?

Since many stars are hundreds of light years away from the Earth and therefore, what we observe of them today is really their distant past, how can we say anything with certainty about their ...
3
votes
2answers
284 views

Dark Matter 'Stars'

I'm aware that the Milky Way has a dark matter 'halo' around it, presumably a spherically symmetric distribution. But I'm completely ignorant regarding the theories explaining dark matter... Is there ...
4
votes
2answers
96 views

What reason(s) exist to suppose that all degeneracy pressures can be overcome in Black-Hole formation?

In models of stellar collapse to a black hole, it is a given that density increases without bound towards a singularity. Electron degeneracy I get. Neutron degeneracy I get. I assume there's some ...
5
votes
4answers
446 views

Are galactic stars spiraling inwards?

Are the stars in our galaxy spiraling inwards towards the center, or are they in a permanent orbit? And if we are heading towards the center then what is the rate of this process? I started ...
2
votes
2answers
206 views

How to calculate gravity inside the star?

Gravity must decrease due to less effective mass when going inside the object but also must increase with depth inside the star due to its higher density. Is there a model or formula approximating ...
2
votes
1answer
48 views

Distinguishing Gamma-rays and stars from each other in nebulas

How do you tell the difference between a gamma-ray burst and a star just from a picture of a nebula, in which it cannot flash on and off here and there?