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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.

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2answers
633 views

What is the significance of Hydrogen column density?

I have always read in the textbooks about star formation and ${\rm H}_2$ column densities. What is the relationship between the two? How is star formation affected by ${\rm H}_2$ column densities?
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How does the intensity of electromagnetic signals change with angular height of a star? [closed]

Suppose a receiver records only the electromagnetic signals coming from a certain star. The vector E (the intensity of the electric field of these signals) oscillates parallel with the plane and ...
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540 views

Observed wavelength of moving distant star (Doppler shift) with hydrogen cloud absorption [closed]

A star is moving away from a stationary observer with known velocity $V_* = 3 \cdot 10^5 m/s$. Between the star and observer, there is a moving hydrogen gas cloud, which is approaching the stationary ...
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The Polaris/Pole star and revolution of Earth

How can we say that the Pole star is fixed just because it is positioned exactly above the North Pole? How does it revolve along with Earth around the Sun if it's fixed?
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866 views

Energy and colours of the stars

We know that stars have different colours because they have different energy. So blue stars have a lot of energy because the blues's frequency is very high $E = h\nu$. The colour of the star is its ...
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1answer
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What is stellar wind in laymans terms and how angular momentum from the star gets transferred to the stellar wind?

The stellar wind ejected by stars is a plasma (i.e., charged) and thus can and does interact with the star's magnetic field. This transfers angular momentum from the star to the stellar wind.
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Why is a point source (star) more twinkling than a disc source (planet)?

Most scintillation effects are caused by anomalous refraction caused by small-scale fluctuations in air density usually related to temperature gradients. Stars twinkle because they are so far from ...
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1answer
75 views

Star formation confusion

If gravity is really a weak force compared to other forces, then how does gravity pull hydrogen atoms in a nebula to from stars. I understand that hydrogen is in atomic or in the molecular state in ...
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1answer
224 views

Stress-energy tensor for radiation from a star

I have been puzzling over an exercise in Schutz's A First Course in General Relativity: Show that, in the rest frame $\mathcal{O}$ of a star of constant luminosity $L$ (total radiated energy per ...
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Why do we see the sun as being yellow, if it is actually white? [duplicate]

How is the light from the sun scattered by the atmosphere in such a way for us to see it as yellow when it is actually white?
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1answer
368 views

Is a Gravastar more dense than a Neutron Star?

Given: A Neutron star is the collapsed core of a larger star; Models for Neutron stars suggest they are composed almost entirely of neutrons; And if: Bose-Einstein condensates are extremely dense ...
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1answer
83 views

Could there be a rocky star, made from silicon, oxygen, etc?

Rocky in terms that it will have mostly silicon and oxygen composition, just like terrestrial planets. But not because it runs out of hydrogen and helium, rather it should start it's life by fusing ...
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Slope of main sequence in HR diagram

In the HR diagram, what causes the change of slope (more flattened) around the area marked with $X$? This corresponds to luminosity of $\sim 1 L_{\odot}$ and temperature $~6000-8000 K$
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1answer
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Compositions of stars at different stages

So I have been trying to find what stars chemical composition is depending on the stage and I have not found anything beyond the "average star" or our sun. For example out the sun and many others ...
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2answers
156 views

How do you find the mass involved in fusion reactions in the center of a star?

How have scientists found the amount of a stars mass that is in the central region where nuclear fusion occurs? For example, our Sun has about 10% of its mass in the center, how have scientists found ...
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4answers
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Can stars contain neutron-star dense cores?

purely for curiosity: are there any conditions under which a small amount of neutron star matter (400 trillion grams per cubic centimeter) could be at the core of a star or planet? neutron star ...
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121 views

Hypervelocity stars sucked in a black hole

As one of the stars spirals in toward the black hole, its companion is flung outward at a tremendous velocity. But why is the second star flung outward?
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1answer
514 views

How much mass do stars lose when turning into black holes?

Is there any way to predict the amount of mass a star will lose when turning into a black hole? I know that the star loses it's outer layers, but is there any way to predict it's final mass?
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1answer
208 views

Energy transport mechanism in stars

I haven't understood the mechanism by which energy from the core of a star reaches its outer layers. Primarily, heat is transfered via convection or radiation. For stars of nearly one solar mass, ...
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Spin during gravitational collapse

During or upon the ending of the gravitational collapse of a rotating star, can it be reasonably hypothesized that a collision between particles of half-integral spin might result either in a change ...
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Plasma and Stars

I have read that most stars are made mostly of plasma. My questions in this statement are: Are there stars not made of plasma? In what percentage stars are made of plasma?
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1answer
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Is it possible that matter mass of a star more than total gravitational mass?

Matter mass of a star can be found from $$M_\rho =\frac{1}{2} \int \rho r^2 dr .$$ On the other hand, there is also gravitational mass of a star in the Schwarzchild metric $$ 1- \frac{2M}{r}.$$ ...
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Is it possible to cook meat using starlight and multiple magnifying instruments

So you can burn a piece of paper with magnifying glass and sunlight. Light from stars are similar to that emitted by the sun, just much, much weaker. Theoretically, is it possible to cook a thinly ...
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1answer
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Can be possible that a neutron star has a negative gravitational surface redshift?

I am looking for some strange stars that is gravitationally blue shifted. A star surface redshift determines mass-radius relation for chargeless star. Can be possible that a charged neutron star ...
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1answer
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Let's make Jupiter a star

It is known that Jupiter is mostly made of hydrogen, but that it is not massive enough to start nuclear fusion. In other words, Jupiter is not a star, but could be a star if someone added hydrogen to ...
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How would a star powered by matter-antimatter annihilation be?

An analogue to our sun or stars but the energy does not come from fusion but from matter antimatter annihilation. If such system could exist, how would it be?
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1answer
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How to find the rising time of constellations at a specific longitude and latitude on earth?

I wish to find the rising time of constellations I am writing a computer program. I have successfully determined the rising time of planets and ascendant (zodiac sign on the eastern horizon) by the ...
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3answers
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How much does surface gravity of a star shift color and who observes the shift?

Reading Richard Muller's new book Now he explains that since the gravitational field near the surface of star causes time to run slower relative to time further away from the surface, the frequency of ...
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How many naked-eye stars have 'died' since they emitted the light we are seeing?

This question is sort of in the spirit of this xkcd: The light we get from stars was emitted many years in the past, but the distances to stars which are bright enough to be visible to the naked ...
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The meaning of “raw materials”

Stars are the most important objects in the Universe--huge balls of gas that grow dense and hot enough to sustain nuclear fusion in their core. They are the ultimate source of all high-energy ...
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Why is the density of the Fermi gas in a neutron star not changing the potential depth caused by the strong nuclear interaction?

In some textbooks, the neutron star is explained as a degenerate Fermi gas. To calculate the degenerate pressure of the neutron fermi gas the average Energy of a neutron, U is calculated when the ...
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4answers
394 views

Can a star collapse into a black hole before it finishes burning its hydrogen fuel?

I don't see why a 50 solar mass star couldn't do so for the following reason. The pressure beyond some depth is so high that the matter below it is degenerate matter despite the very high temperature ...
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Is it possible to have a hollow star?

Let's say that there existed a non-rotating hollow shell of hydrogen gas in space. This shell of gas was collapsing under its own weight. Is it possible to form a star that is hollow inside? If the ...
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How is it that we can detect CMB radiation but not the first stars and galaxies despite CMB originating from before the first stars were born?

The CMB originates from when the Universe became transparent, around 380,000 years after the Big Bang, and stars were born around 100 million years later. I know the first stars and galaxies aren't ...
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370 views

Can Hydrogen Fusion via CNO Cycle Occur in First Generation Stars

CNO cycle requires the presence of carbon, nitrogen and oxygen to undergo hydrogen fusion. Does this mean that for first generation stars, no matter how big they are, can't undergo hydrogen fusion by ...
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Is the mass of an individual star almost constant throughout its life?

Could we say that an individual star is almost a closed system?, as many of the stars like the sun don't exchange significant amount of their mass with their environment (except solar flares & ...
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Why are pre-main sequence stars brighter than they will be on the main sequence?

Why is a pre-main sequence star brighter than it will be when it reaches the main sequence?
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Are we closer to an accurate 3 D image of our galaxy using the Gaia billion star data set?

From the BBC: Report on Gaia Mission Data 14th September 2016 Astronomers working on the Gaia space telescope have released a first tranche of data recording the position and brightness of over a ...
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Calcaluting mass with density different integral methods different results?

I need to calculate the following mass with given density. I know that the density is : $p(r)=p_{0}\frac{r}{R}$. The problem is that in the book they ask to calculate the mass yet in two different ...
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198 views

How do stars survive their own gravitational pull?

I read that stars burn hydrogen and helium to fight against gravity. How does burning something help against gravity?
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57 views

Is there a mass relation of the core left behind after ejection in a red giant?

Assuming that you have the mass of the star prior to the ejection of non-core material, is there any relation that can be used to approximate the mass of the resulting left behind core which will ...
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1answer
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Assuming that you have the mass and age of a star, can you determine the most likely current class?

I am asking for the purposes of generating realistic stars. Assuming that you have the inputs of the mass of a star, and its age, is there any method for determining its class and state?
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3answers
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why do hypergiants shed mass before death?

I'm reading on this website here and will be using lots of quotes from it. Hypergiant Star Seen Shedding Mass Ahead Of Explosive Death As Supernova Astronomers using a telescope in Chile have ...
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For a collapsing star, at what mass is the formation of a black hole inevitable?

Stellar mass black holes are formed from the collapse of stars. I have read figures, normally around 2-3 solar masses, that correspond to the mass at which it becomes inevitable that a star will ...
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what is the telescopic retinal illuminance of a star?

What is the retinal illuminance (in trolands) or luminance (in $cd/m^2$) of a star image viewed through a telescope? I'm looking for a formula that will calculate this value for input values of star ...
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1answer
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How do we know singularities/black holes actually bend time?

Recently I read up on some articles about singularities / black holes, how they form and how they affect their surroundings. Just to clarify, I am no physicist and I found those articles on the ...
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Number of stars with apparent flux

The stars in our Galaxy have luminosities ranging from $L_{\text{min}}$ to $L_{\text{max}}$. Suppose that the number of stars per unit volume with luminosities in the range of $L$, $L+dL$ is $n(L)dL$. ...
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Influence of matter of a star on masses of neutrinos

It is well known that if neutrinos has masses then from Dirac equation it follows that they propagate (in vacuum) as a eigenstates of mass (not as eigenstates of interaction). It's wave function is of ...
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1answer
686 views

Resource: Star map which show current actual positions versus current observable positions?

Light travelling from stars and galaxies takes some time to reach us here on Earth - when we observe stars or galaxies in the night sky, we see their positions as they were when the light left on its ...
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Can elements heavier than iron be present in a star's core?

My understanding is that elements heavier than iron and nickel are not formed in a star but, can heavy elements such as lead and others be present/found in a star's core ? I ask because the following ...