Questions tagged [stars]

Stars are astronomical bodies that are (usually) mainly composed of Hydrogen, Helium, and Lithium. They are massive enough that their gravity compresses the matter to the point where nuclear fusion occurs, which creates a lot of heat and tends to make stars output radiation along a blackbody curve. Typically the radiative output is significant in the visible spectrum making stars very bright objects.

Filter by
Sorted by
Tagged with
2 votes
2 answers
180 views

How to measure the ratio of a planet's radius to a star?

I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information. One of ...
Bml's user avatar
  • 359
1 vote
2 answers
72 views

Number of red giant phases for stars between 2.2 - 8 solar masses

It is my understanding that stars the size of our sun will go through two red giant phases. The first one will occur when fusion of hydrogen to helium begins to happen in a shell surrounding the ...
user12277's user avatar
  • 343
4 votes
0 answers
59 views

Hills Mechanism

The Hills mechanism postulates that when a stellar binary system is perturbed by a supermassive black hole (SMBH), the tidal forces at play result in the capture of one star while simultaneously ...
RKerr's user avatar
  • 1,151
8 votes
3 answers
4k views

What is the most highly charged celestial body in the universe?

Generally speaking, the universe is electrically neutral and the universe abhors an unbalanced charge. Wherever there is a positively charged object, you can bet there is a negatively charged object ...
enigmaticPhysicist's user avatar
0 votes
1 answer
41 views

Color temperature and space

I often think about the universe and lately about the color spectrum. so I wanted to ask how much the temperature of the body depends on the color. the hottest star I've found is 200,000 k and its ...
David Hačko's user avatar
0 votes
0 answers
18 views

How fast is the naked-eye visible transition of a main sequence star to a giant? [duplicate]

I know the evolution of a main sequence star to a giant is a process that takes millions and millions of years, but how fast is the VISIBLE change? Basically, will our sun, for example, slowly grow to ...
blacktopshaman's user avatar
14 votes
2 answers
912 views

Is gravitational binding energy or gravitational self-energy a source of gravity?

The gravitational binding energy or self-energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. Equivalently, the ...
Manuel's user avatar
  • 478
1 vote
0 answers
88 views

How can there be supermassive stars of 10000+ solar masses?

Wouldn't such supermassive stars blow themselves apart first via radiation pressure (per the Eddington limit)? But they apparently exist, or at least are plausible: Assistant Research Fellow, Ke-Jung ...
Allure's user avatar
  • 19.7k
0 votes
0 answers
15 views

Luminosity effect in stellar spectral classification

“Atoms with small ionization energy,Ir,will have a higher ionization in the atmospheres of giants than in those of dwarfs, and the atoms with large Ir will behave in the opposite way. This ...
teacher's user avatar
  • 327
0 votes
1 answer
36 views

Salpeter mass function - past paper question [duplicate]

I'm doing a past paper and this is the question I'm struggling with (it's a standalone question with no other information given outside of this screenshot): To answer it, I used the Salpeter mass ...
user374355's user avatar
1 vote
2 answers
110 views

What is the total energy of newtonian polytrope stars of index $n > 5$?

In classical newtonian theory, we could find a general expression for the gravitational potential energy of a polytrope sphere (of pressure $p(\rho) = \kappa \rho^{\gamma}$, where $\gamma = 1 + \frac{...
Cham's user avatar
  • 7,073
1 vote
1 answer
149 views

What is the equation of state (EoS) of a polytrope in general relativity?

I'm trying to numerically integrate the TOV (Tolman-Openheimer-Volkof) equations, using Mathematica. The code works, but I'm having issues with the polytropic equation of state (EoS). The equations ...
Cham's user avatar
  • 7,073
0 votes
2 answers
81 views

What are the hex color code equivalents for the different classifications of stars?

Stars appear to be of various colors based on the visible light they emit. I am wondering if there is a hex color code that can be considered to be typified or average for the various classifications ...
nijineko's user avatar
  • 143
1 vote
0 answers
52 views

Olbers' paradox and thermodynamics? [closed]

So consider our universe as an isolated system which has reached thermal equilibrium. Now using the first law of thermodynamics: $$ \underbrace{T dS}_{\text{Total energy}} = \underbrace{P dV}_{\text{...
More Anonymous's user avatar
4 votes
1 answer
184 views

Could electron "Stars" exist? [duplicate]

Is there a point of balance where the gravitational pull of a sphere of electrons is equal to their electromagnetic repulsion? That is to say, could it be possible to create stars that are made purely ...
Nick Revenco's user avatar
4 votes
1 answer
81 views

Will Hawking radiation violate baryon number conservation around gravitating bodies other than black holes?

Numberous articles discussing a recent research paper suggest that even stars and planets will eventually radiate away their mass like hawking radiation. My question is will this violate baryon ...
Keith Reynolds's user avatar
0 votes
1 answer
34 views

Effect of Sun temperature on the thermosphere

Correct me if I’m wrong here. The thermosphere is hot due to its absorption of moderately high energy UV radiation. (<200nm) Cooler stars emit fewer high energy photons. So if the Earth orbited an ...
blademan9999's user avatar
  • 2,830
0 votes
2 answers
97 views

What’s the lightest you could make a "star" if you made it out of different materials?

What’s the lightest you could make a "star" if you made it out of different materials? How large would the "star" be? For example according to here https://astronomy.stackexchange....
blademan9999's user avatar
  • 2,830
0 votes
1 answer
56 views

What's the nearest star that could go Supernova in the near future?

https://en.wikipedia.org/wiki/IK_Pegasi B is the nearest supernova candidate, but that white dwarf that's part of the system won't go supernova for around 2 billion years. What's the nearest star that ...
blademan9999's user avatar
  • 2,830
7 votes
2 answers
177 views

Why are black holes sometimes formed without supernovae?

I've heard that very massive stars can sometimes collapse into black holes without creating supernovae. How does this happen? (I suspect it's something to do with the relative lack of Urca process ...
blademan9999's user avatar
  • 2,830
2 votes
2 answers
692 views

Making sense of the Jeans mass

The Jeans mass, given by $M_J=\sqrt{\left(\frac{-5k_BT}{Gm}\right)^3\cdot\left(\frac{3}{4\pi\rho}\right)}$, is the threshold mass a dust cloud must have in order to begin gravitationally collapsing ...
AlanFox86's user avatar
  • 311
0 votes
1 answer
66 views

What’s the minimum mass required for a star to burn helium?

What’s the minimum mass required for a star to burn helium? I’ve liked online but I’ve gotten inconsistent answers.
blademan9999's user avatar
  • 2,830
0 votes
1 answer
27 views

Difference between star formation rate and star formation history

When we speak about galaxies evolution, what is the difference between the star formation rate and the star formation history?
Daniele Zambetti's user avatar
0 votes
2 answers
56 views

Time of collapse of stellar dust cloud

A stellar gas cloud collapses onto itself once it reaches Jean's mass, and the time it takes for said cloud to collapse is given by: $t_{coll}=\sqrt{\frac{3\pi}{32G\rho_0}}$, where $\rho_0$ is the ...
AlanFox86's user avatar
  • 311
0 votes
0 answers
31 views

Dynamical instability and thermal instability

I'm studying instability in Stellar Dynamics (in particular globular clusters instabilities). I have not understood clearly the definition of these concept. Dynamical instability is the study of the ...
nervousdog's user avatar
3 votes
1 answer
74 views

How many type II supernovae are there per stellar mass formed?

I have been searching for the number of type II (core-collapse) supernovae per unit of stellar mass formed. It is my understanding that a star must have an initial mass of at least 8 times and no more ...
sav's user avatar
  • 31
0 votes
3 answers
59 views

How line of sight is determined?

How do they calculate the line of sight of a galaxy or binary star system from an observer's point of view. the velocity of a star in a binary star system depends on the line of sight so how do they ...
starwatcher_65's user avatar
1 vote
1 answer
123 views

Numerical Integration for White Dwarf Model [closed]

I'm creating a numerical integration model of a white dwarf. So I've started with calculating electron pressure vs number density across a wide range of values. Using the equations of state in ...
Celina Emma's user avatar
1 vote
2 answers
129 views

Star with quadrupole in binary system violates Newton's 3th law?

Suppose that, in a binary system of two stars, the star A (and only the star A) has a non-zero quadrupole moment $Q_A$. Then, the star B feels the usual gravity force plus an additional force, ...
gravitone123's user avatar
8 votes
2 answers
641 views

At what distance can I assume peculiar velocity is negligible compared to expansion velocity, to use Hubble's law?

I am working on a high school physics assignment and am trying to figure out a method to determine if the star is a giant or main sequence from its spectral and photometric data (from SDSS). I picked ...
Hossam Dahshan's user avatar
9 votes
2 answers
1k views

Why don't less massive stars explode in form of supernovas?

I'm a high school student with a question about supernovas and the life cycle of stars. I understand that supernovas occur in massive stars when they run out of fuel and collapse, resulting in a ...
Authentic Melody's user avatar
0 votes
0 answers
25 views

The role of gas pressure in the life cycle of stars

As a high school student, I am curious about the significance of gas pressure in the life cycle of a star. While I have read about the radiation pressure and the pressure caused by the energy released ...
Authentic Melody's user avatar
3 votes
1 answer
86 views

Color temperature or effective temperature?

I am a high school student interested in astronomy and physics, and I am trying to understand the difference between color temperature and effective temperature of a star. As I have searched this ...
Authentic Melody's user avatar
0 votes
2 answers
25 views

$y$-axis on HR diagram

I have an exercise where I have to determine the luminosity of a star with 10 000K. However, I'm confused about how to read off the $y$-axis on the graph when the scale is uneven. What is the function ...
dreamer567's user avatar
1 vote
1 answer
19 views

Star equations of hydrostatic equilibrium for a mix of 2 fleebly interacting gases/fluids and interaction term

For a single matter species, the equations of hydrostatic equilibirum for a star are \begin{eqnarray} \nabla^2 \phi &=& 4\pi G \rho\\ \vec{\nabla} P + \rho \vec{\nabla}\phi &=&0 \end{...
Giorgio Busoni's user avatar
0 votes
1 answer
91 views

Can I find the surface temperature of the Sun using a spectrometer?

So I have a high school physics project and I essentially have this experiment idea where I use spectroscopy to find the surface temperature of the sun. Now I'm essentially going to assume the Sun is ...
TheExplorer22321's user avatar
2 votes
2 answers
156 views

Can a massive star become a red giant more than once?

Massive stars may undergo multiple fusion processes as they near the end of their lifespans. Our sun will eventually start fusing helium in its inner core so that carbon is formed. As this occurs, the ...
user12277's user avatar
  • 343
3 votes
1 answer
51 views

Can the quark-gluon plasma of the very early universe be accurately characterized as a type of quark star?

The very early universe was dense and opaque. During the quark epoch, the entirety of the universe, up to every boundary, was a filled-in ball of QGP. Much like a star is a ball of ionized nuclei that ...
blacktopshaman's user avatar
1 vote
1 answer
28 views

Should blue & white stars appear red and inflated while observed on the lower part of the night sky for the similar reason as the Sun during sunset?

Should blue and white stars appear red and inflated while observed on the lower part of the night sky for the fairly same reason as the sunlight during sunset? As these stars emit blue light ...
Krešimir Bradvica's user avatar
2 votes
1 answer
678 views

Is the temperature of the hottest star's core known?

WR 102 is believed to be the hottest star in the observable universe, whose surface temperature is $210,000 ^\circ K$. But the related wikipedia entry does not say anything about the temperature of ...
user avatar
1 vote
0 answers
51 views

In a non-rotating sphere of fluid heated from the centre, what does the flow look like?

Consider a perfect sphere of fluid which is not rotating, is under the influence of its own gravity only, and is heated from the centre. What does the flow of fluid in the body look like? In the ...
rake's user avatar
  • 11
1 vote
0 answers
22 views

Stellar classification: Luminosity class

So in the astrophysics textbook by Carrol and Ostlie, when the luminosity class is discussed, it has such a sentence "The ratio of the strengths of two closely spaced lines is often employed to ...
ABC's user avatar
  • 161
0 votes
0 answers
29 views

Finding chemical equilibrium with an application to the Sun

Consider the following reversible reaction: $\rm H_{2}{\rightleftharpoons}2H$. To find chemical equilibrium, we use the chemical equilibrium constant. There are two equations for the chemical ...
Cesare's user avatar
  • 23
14 votes
3 answers
3k views

Is it possible to tell the difference between a young star that is just "big" and an older red giant?

I read the Wikipedia page for one of the biggest known stars, UY Scuti, and was curious to see the age of the star isn't really known at all. When a star's hydrogen fuel is exhausted, it starts ...
MFerguson's user avatar
  • 243
1 vote
1 answer
64 views

What would the nucleus of a water planet be like?

If we have a planet made out of water, would it be all solid? What about the nucleus? Would it depend on the size of the planet?
Pablo's user avatar
  • 141
0 votes
1 answer
223 views

How long will Brown Dwarfs live?

Brown Dwarfs are a technical star because of their masses. If Red Dwarfs live for 10 trillion years, then how long could Brown Dwarfs live?
Some Hair in a room's user avatar
2 votes
1 answer
194 views

Does the Sun increase entropy?

The Sun generates heat via fusion. The heat from this reaction gets distributed around the solar system and beyond. This process of spewing heat and radiation all over the place doesn't immediately ...
Him's user avatar
  • 299
-1 votes
2 answers
64 views

Star gets eaten and spit out?

How does material get swallowed and torn apart by a black hole and have its light vanish. But somehow the same material escapes years later. After its light couldn't even escape? They watched it for ...
Justin Dougherty's user avatar
5 votes
1 answer
32 views

Why is the common envelope ejected in some accretor-donor systems?

As an example, let us consider a binary system of a neutron star and an evolved star (e.g. red giant) that has expanded, filled its roche lobe, and started the mass transfer onto the neutron star. ...
Gianluca's user avatar
3 votes
1 answer
324 views

Why are certain stars not moving in this timelapse video?

In this video, certain stars are not moving in the bottom left & top right corners. I thought only the pole star didn't move. https://www.youtube.com/watch?v=QC8iQqtG0hg&ab_channel=...
Shirish Srivastava's user avatar

1
2 3 4 5
16