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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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Molecular cloud and star formation surveys

I just had a quick question about molecular clouds. Why is it that we survey them using $CO$ lines instead of $HII$? Is it because $CO$ has better emission? It doesn't make sense to me when I read ...
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The intensity of light coming from a distant star [on hold]

The intensity of light coming from a distant star is measured using two identical instruments A and B, where A is placed in a satellite outside the Earth’s atmosphere,and B is placed on the Earth’s ...
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Query concerning black holes [duplicate]

What information can be conveyed from a black hole about the substances and radiations it absorbs into it's singularity.
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63 views

Thermal fission of gold?

Here's a slightly silly idea that arose from this question "What elements would be created in a star composed entirely of gold?": If we accumulate a lot of gold (really a lot) fast enough, it will ...
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Theoretically, Is it possible to create a nova by firing large masses into a sun?

In a science fiction story (Bobiverse) a nova is created by accelerating two small planets at relativistic speeds into a sun from opposite sides.The shockwave creates hydrogen fusion on opposite sides ...
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What would Happen if a Primordial Black Hole, with 5-10x time the mass of Earth, were to fall into our Sun?

So lately i heard of this theory that planet 9 might be a Primordial Black Hole (PBH) with 5 - 10 times the mass of Earth. I was thinking to myself, what would happen, if such a PBH (if it even exists)...
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Could Alpha Centauri be made of anti-matter? [duplicate]

How can we tell if a star is made of matter or anti-matter? For example, is there any difference spectroscopically? Or could we tell from cosmic rays? If half of the stars were made of matter and ...
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Can someone calculate the age of the KOI-4878 star?

The star’s low metallicity and fairly high space velocity suggest that KOI-4878 is older than the Sun. But I don't know how to calculate an estimation for the age. KOI-4878 data on Simbad: http://...
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Looking for a good book on star stability

Can anyone recommend me any resources from which I could learn about how stars maintain a stable form, maybe using some thermal and nuclear physics, and maybe fluid dynamics, but not so advanced. ...
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What conditions provide the oldest star?

If we define the start of the lifetime the protostar and the end of the lifetime a red giant (at max volume), what conditions would make this time the longest when the star was first formed and ...
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Shooting Star Anomaly

Tonight I was walking home from the supermarket and saw an unusual shooting star. It appeared at a point in the sky, bright red and accelerated to a visible extent far faster than any other shooting ...
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Why is the spectrum of a star pretty much continuous? [duplicate]

I was reading about the development of the quantum theory when I got to the explanation for spectral lines. It's a topic that I've revisited many times but I came up with a question. I know that in ...
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Can an observer perceive a single source of light as multiple sources because of curved spacetime?

Is it possible that some of the stars and galaxies we observe here on Earth are actually replicates of other stars and galaxies we are observing from different angles because of curved spacetime? Let'...
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Do post-big-bang quantum fluctuations determine star and planet formation?

It is my understanding that cosmology simulations largely implement general-relativity, taking quantum-effects into account merely by setting the fluctuations in the initial conditions. In the real ...
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Can Thorne–Żytkow object (heavenly body) exist in universe?

Can Thorne–Żytkow object (heavenly body) exist in universe? It's a new concept I came across. Are there such heavenly bodies in universe? It's a heavenly body in which a neutron star is present inside ...
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If I add more mass to a red giant, will it become a supergiant?

Let's say I have a red giant. If I start dumping more matter onto it, will it eventually become a red supergiant? I'm guessing the answer is "yes" because when I see this covered in textbooks, they ...
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Metric for a rotating star

If we want to describe a static spherically symmetric star we can use a metric which matches the Schwarzschild solution with correct mass on the outside of the star but differs from Schwartzschild in ...
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How do we determine both the distance to and speed of distant stars?

My understanding is that we can measure the distance to far away stars by using their color to infer the absolute magnitude of the light they emit and compare that to the observed magnitude of the ...
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Theoretical values of radius and mass of O9.5 II star?

Where to find please theoretical values of radius and mass of O9.5 II star? I mean something like: http://www.mpe.mpg.de/~martins/pub/calib_Ostar.pdf However, there are only O I, O III and O V stars ...
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In what planetary system can we have arbitrarily long winters?

Unlike on Earth where the length of seasons are almost of the same duration each time, the hypothetical planet on which Game of Thrones took place has seasons of arbitrary length i.e. some winters ...
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Can a gas cloud of pure helium collapse and ignite into a star?

Assuming there could be a giant gas cloud with negligible amount of hydrogen and metal (elements with atomic number $Z\geq3$), could it collapse gravitationally and form a pure helium star that would ...
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Why hydrogen lines are less visible in the Sun spectrum than in supernovae clouds?

Supernovae clouds are very colorful, and if I trust documentaries I watched, the colors are due to excitation of elements, as in fireworks. Since the Sun is mostly made of hydrogen, I suppose those ...
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Why is the Sun made of light elements only?

Since the entire solar system inherits its heavy elements from supernovae unrelated to our star, I fail to understand why, while capturing most of said system's matter, the sun only contain light ...
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Star formation after big bang doesn't violate entropy? [duplicate]

Ok I know this has been asked a lot but I'm still a bit confused. After big bang, there are a lot of equally distributed elementary particles around with evenly distributed heat(or photons). So why ...
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CNO-cycle in Population III stars [duplicate]

It has been stated several times here and probably elsewhere that the first population III stars were unable to undergo H-to-He fusion via the CNO cycle as there was virtually no carbon-12 at the ...
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Why does a drop in gravitational energy result in star contraction

Consider a gas cloud that is radiating away heat. From virial theorem we see that if the cloud radiates away heat and loses energy this will cause its gravitational energy to drop. Why does this mean ...
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What is the relationship between the absolute magnitude and power output of a star?

I can't seem to find a straight answer online. Is the absolute magnitude of a star equal to / linearly proportional to / or unrelated to the power output of the star. When I say absolute magnitude I ...
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Why light coming from distant stars is not discrete? [duplicate]

Imaging the light racing out from distant sun, as beam of light shoots aways is a circular pattern (spherical actually), remembering that, light comes in photons or packets of energy. so how come is ...
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Dimensional grid of spatial coherence on earth of Pole Star radiation

One spot on earth receives a constant stream of stellar radiation: this is the North Pole where the Pole star radiation flows constantly. Given that a point source of light is considered to emit a ...
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Is there a relatively painless way to calculate the radius of a neutron star, given its mass?

I know there are different models based on, as I understand it, different equations of state describing the neutron star mass-raduis relation. I'm not sure what to do with that, though. My math isn't ...
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Is it possible to form a toroidal star?

Perhaps a fast spinning star (not spherical) where a black hole forms in the center, but the event horizon is smaller than the equatorial radius but larger than the polar radius?
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black dwarf stars and dark matter

Today we understand that a black dwarf star represents a hypothetical star that is the result of the complete consumption of the energy of a white dwarf which is the remnant of a star of little or ...
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Behaviour of a star as it approaches Ultrarelativistc limit

By considering the potential energy of a degenerate star of mass $M$ and radius $R$, I can use dimensional arguments to show that the radius of the star depends on its mass as: $$ R ∝ M^\frac{2-n}{...
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Can a star visually look like a black hole? [duplicate]

Amateur question incoming so please bear with me. Assumptions If a black hole is born from a star going supernova, intuitively it should have the same or less mass compared to the star. Black holes ...
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What percentage of stars are giants/subgiants/main sequence etc

I am trying to find the percentage of main-sequence stars along with red-dwarf percentage for my research paper. I did find one article regarding, however it is very old and i require recent data ...
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Is the Universe an isolated system? [duplicate]

I am not a physicist but this question has bugged me for a while now. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. However, if the ...
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How is it possible to see stars-light, from stars millions of light years apart with the naked eye? [closed]

How is it possible for us to see stars that are millions of light years 'APART' from one another with the naked eye when we look at in the night sky from horizon to horizon? (i.e., pick any stars ...
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Energy budget of of proton-proton fusion (p-p chain)

How much energy is released in the first nuclear reaction of the p-p chain which produces energy in lower-mass stars like the Sun? The value of 1.44 MeV is given in many sources, but I don't ...
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Does a star need to be inside a galaxy?

Must a star belong to a galaxy, or could it be completely isolated? In case it can be isolated (not belong to a galaxy), could it have a planet orbiting around it?
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Event horizon and the existence of point particles

In this paper by David Kuap that first introduced the concept of Boson stars, he states that when the Einstein-Klein-Gordon system of equations is solved, the solutions obtained do not account for an ...
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1answer
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How did Edwin Hubble estimate the velocity of distant stars?

I didn't know how to be succinct with my actual question in the title. My question is, how did he separate the components of the actual velocity of stars from that of the velocity due to recession (...
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Treating stars and planets as a blackbody determine the temperature of a planet that has EM radiation incident upon it from a star

Consider the following question: Power emitted by the star via the Stefan Boltzmann law is as follows: $$4\pi\sigma T_s^4 r_s^2 $$ However the power will drop over distance and so we can say that ...
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Do only 'giant stars' fuse large amounts of elements other than hydrogen and helium?

Do only giant stars initiate 'full-on' carbon (and higher element) fusion, even though red giants on the larger end of the spectrum create carbon and oxygen via producing helium per the CNO cycle?
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Why does a star die once it has iron?

I found out that iron is the death element for stars, but I couldn't find why can anyone knowledgeable on stars explain why iron causes the star to die?
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Do supernovae push neighboring stars outward?

I know that a supernova can mess up the heliosphere of nearby stars, but I'm wondering if it could physically push neighboring stars off their trajectories. It's fun to imagine all the stars ...
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1answer
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Doubts about the formation of the bullet cluster

The bullet cluster is formed by the collision of two clusters of galaxies. After the collision, the stars and galaxies in those two clusters passed through each other. But the intergalactic gas clouds ...
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1answer
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Forming a Neutron Star: inverse $\beta^-$ decay or electron capture?

There are three different kinds of beta decays: $\beta^-$: n $\rightarrow$ p + e$^-$ + $\overline{\nu}_{e^-}$ $\beta^+$: p $\rightarrow$ n + e$^+$ + $\nu_{e}$ electron capture: p + e$^-$ $\rightarrow$...
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Naive question about Gravitational collapse

Suppose that you have a probe orbting a $10M_{\odot}$ star in the final moments before gravitational collapse. In a time $t$ the collapse event occurs. So do you really would see all the matter "...
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Would a Dyson sphere face physical limits faced by white dwarves?

During a recent online discussion, one of the participants made the claim that a Dyson sphere would be limited in mass by the Chandrasekhar limit. Attempts to solicit evidence for this claim were ...
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Wildly Inconsistent Answers Re: A Teaspoon of Neutron Star versus the Giza Pyramid

I'm experiencing a mild fit of nerd-rage here and I'm hoping someone can help. I was watching a documentary and it made a claim I've heard a few times before: that a teaspoon of material from a ...