What is Star: Definition and 1000 Discussions

A star is an astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but due to their immense distance from Earth they appear as fixed points of light in the sky. The most prominent stars are grouped into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars, but most are invisible to the naked eye from Earth, including all individual stars outside our galaxy, the Milky Way.
A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. The total mass of a star is the main factor that determines its evolution and eventual fate. For most of its active life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. At the end of a star's lifetime, its core becomes a stellar remnant: a white dwarf, a neutron star, or, if it is sufficiently massive, a black hole.
Almost all naturally occurring elements heavier than lithium are created by stellar nucleosynthesis in stars or their remnants. Chemically enriched material is returned to the interstellar medium by stellar mass loss or supernova explosions and then recycled into new stars. Astronomers can determine stellar properties including mass, age, metallicity (chemical composition), variability, distance, and motion through space by carrying out observations of a star's apparent brightness, spectrum, and changes in its position on the sky over time.
Stars can form orbital systems with other astronomical objects, as in the case of planetary systems and star systems with two or more stars. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.

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  1. D

    Star Opacity and Balmer Break

    I am not sure where to start for this. Considering it needs to be demonstrate Balmer Break, I am assuming it needs to be wavelength based. As a result I am assuming I cannot use mean (Kramers) Opacity but rather express in terms of Opacity k= n*sigma/rho. My thoughts are to use Boltzmann...
  2. V

    B Time Dilation: Traveling to a Distant Star in 4.5yr

    If there is a spaceship traveling at 0.999c, the time to reach a star 100 lyr away would be approx 100 yr (assuming no accel and decel). But on the spaceship, It would be 100 yr * sqrt(1-0.999^2) = 4.5yr. Why do we take 100 yr as the time seen on Earth and not the time on the spaceship?
  3. BWV

    Star Builders: Fusion 30 Years Away?

    Ordered the book https://www.amazon.com/dp/B08QXYBNJP/?tag=pfamazon01-20 https://www.nature.com/articles/d41586-021-02203-4 after listening to this podcast: One interesting tidbit - the editors of The Economist apparently banned writers from using the 'fusion is 30 years away and always...
  4. M

    Could the Star Wars galaxy possibly be a void galaxy?

    A void galaxy is a galaxy that exists in a cosmological void like the Bootes void. Most galaxies are clustered into filaments. Here is a link to the Wikipedia page for a void galaxy https://en.m.wikipedia.org/wiki/Void_galaxy Anyway, in Star Wars Legends, the Star Wars galaxy has 7 companion...
  5. DhruvSorathiya

    I Simulating Star Images for Star Tracker Testing

    I am working in a student satellite team and we are working on development of star tracker. So for the testing of it, we will simulate some star images on LCD, but the problem is that rays coming into the star tracker should be parallel as original stars are at infinity. So my question is that...
  6. Buckethead

    B Why would this star move outward?

    I read this (relavant text made bold): "In the study, published in the Monthly Notices of the Royal Astronomical Society, researchers analyzed Gaia space telescope observations of a large group of stars, the Hercules stream, which are in resonance with the bar -- that is, they revolve around...
  7. N

    B Star visible for longest time from Earth

    I was just looking up at the stars wondering how long they have been visible for. I started wondering if any of them might have been around this galactic neighbourhood long enough and long lived/old enough that the dinosaurs could have seen it. Do you think they’d be any? If not what might be a...
  8. G

    I Light Emission by Stars: Mass, Red Shift & Hubble's Law

    Light emitted by a star should be gravitationally red shifted by its own mass, resulting in greater red shift of light emitted by a more massive star. Is this phenomenon known? Could this be contributing in Hubble 's law in some part too-- probably more distant stars are more massive too-- just...
  9. T

    I Stress-Energy of Star Collapsing into Black Hole

    As a black hole is described by a vacuum solution of Einstein's field equations the stress-energy tensor vanishes identically zero. If one assumes the mass of a black hole to be "within" the singularity then it seems there is no sensible way to apply the stress-energy tensor to a point. So...
  10. M

    Mysteries of hyperspace in Star Wars?

    I was reading the Star Wars YT-1300 Complete Reference Manual and it mentioned that their are some aspects of hyperspace that remain a mystery aside from those well-established facts acknowledged by all competent astrophysicists. What could be one of the main mysteries? I can’t think of any.
  11. Haorong Wu

    How to model light from a star?

    I am aware that a laser could be modeled as a Gaussian beam, e.g., $$E=E_0\frac{w_0}{w_z}\exp (\frac {-r^2}{w^2_z}) \exp (-i(kz+k \frac {r^2}{2R(z)}-\psi(z))).$$ Now I want to study the propagation of light emitted from stars. But I am not sure how to model it, especially by some kind of...
  12. E

    I Precession of a spherical top in orbit around a rotating star

    Looking at L&L's solution to problem four of section §106. Lagrangian for a system of particles:\begin{align*} L = &\sum_a \frac{m_a' v_a^2}{2} \left( 1 + 3\sum_{b}' \frac{km_b}{c^2 r_{ab}} \right) + \sum_a \frac{m_a v_a^4}{8c^2} + \sum_a \sum_b' \frac{km_a m_b}{2r_{ab}} \\ &- \sum_a \sum_b'...
  13. SJay16

    How would one estimate the rotation period of a star from its spectrum

    The figure is shown; the measurements were taken on two consecutive observing nights. The Ordinate is the flux normalized to continuum and the abscissa is the wavelength scale. You can see the "bumps" indicated by the arrows referring to some Starspot as the spot moves on the profile; assuming a...
  14. yecko

    Comp Sci What is Node and Edge Betweenness in Star Network?

    What is "node betweenness of node 0", and" edge betweenness of edge e01" in the question = ? What is B there in the solution? why e34 calculated instead of e01? (as highlighted) Thank you
  15. Lilian Sa

    Star collapse in general relativity — pressure as a function of star radius

    What I've done is using the TOV equations and I what I found at the end is: ##e^{[\frac{-8}{3}\pi G\rho]r^2+[\frac{16}{9}(G\pi\rho)^{2}]r^4}-\rho=P(r)## so I am sure that this is not right, if someone can help me knowing it I really apricate it :)
  16. E

    Which is your favourite Star Wars film? [3 votes]

    Bit of fun. Vote for your top three!
  17. E

    Black body radiation -- Spherical shell surrounding a star

    I don't understand how this can be solved. The official solution was: F=\sigma*T^4 E=F*4\pi R^2*60*60 This doesn't make sense to me, as it seems to imply that the energy that the black body radiates depends on the radius of the shell. For a very large shell the body will reflect...
  18. cybernetichero

    Orbital mechanics question about Star Trek

    I'm watching the Next Generation episode Relics and Riker has just ordered the helm to "go into orbit above that point" which I took to mean geosynchronous orbit. No biggie except that the point is on the outer surface of a Dyson Sphere with a RADIUS of more than 1AU. So, assuming the sphere has...
  19. HalJordan2814

    How fast is the star moving? (Doppler effect)

    A type of star that usually emits light at a frequency of 6.00 × 10^14 Hz appears to emit light at a frequency of 6.01 × 10^14 Hz. Calculate how fast the star is moving, and if it moving towards us or away from us.
  20. B

    B Collapse of a neutron star - strong nuclear force vs gravity

    I understand that gravity causes a neutron star larger than about 10 solar masses to collapse into a black hole. I also understand that gravity is the weakest of the four forces. So I find this counterintuitive and I'm puzzled that why is it gravity that causes the collapse and NOT the strong...
  21. Y

    I 9 y.o. question: will a spoon of neutron star matter explode?

    Greetings All, Well, this is the question from my 9 y.o. son: what will happen if a famous Everest heavy spoon of neutron star matter is actually removed from the star? I am inclining to his version that it will explode rather quickly, e.g. neutrons will quickly decay into protons-electrons...
  22. Mikkel

    Measure the distance to a star using magnitude and extinction

    Hello, I'm struggling with this question A star is observed close to the center of the Milky Way and from its spectrum we find that it is a type A3 star. Its observed magnitude is m_v = 25. There is only a diffusive gas between us and the star, so we can assume an extinction, of 1 magnitude per...
  23. BWV

    B Star at black hole event horizon

    Curious if the time dilation at the edge of an event horizon would have the apparent effect of prolonging the life of the star to an outside observer - so for example a blue hyper giant at the edge of an event horizon with an expected main sequence time of, say, 500 million years, would remain...
  24. K

    I Help - Derivation of Pulsating Star Euler ODE

    to I am a bit clueless on how to get break the ##r X(r)## from inside the derivative.P.S. I tried to copy from Symbolab instead of pasting the picture, but it didn't let me.
  25. K

    I What happens to a small star after burning all of its fuel?

    Hello! As far as I understand, after a star reaches iron in its core, if it is not massive enough it turns into a white or brown dwarf. What happens when all the energy of the dwarf is gone? Are we left with a huge sphere made almost entirely of iron?
  26. DaveC426913

    Using a solar mirror to deflect a star

    I just finished Stephen Baxter's Manifold: Space. Great writer. Vast worlds he builds. In it, he has a project to deflect a star (a neutron star, to be exact) using a colossal mirror-sail placed on one side of the star. The idea is that the solar radiation bounces off the mirror and is...
  27. Michael_L

    I How to find the distance from a star to the center of the Milky Way Galaxy?

    The distance of the sun to the Galactic Center is about 7.4–8.7 kiloparsecs. If I use the known data of stars in various stellar catalogues, how can I calculate (approximately) a distance of a given star from the Center? What kind of data I need to look for? can it be calculated from Right...
  28. S

    B Why is the momentum of a star equal to the momentum of a planet?

    I was wathcing a video about radial velocity method for seeking exoplanet(video) and on 3:05 author writes that momentum of a star equal momentum of a planet. Why?
  29. Lucy_1192

    I Are Intensity and Magnitude independent of the radius of a star?

    For a star.. Apparent Magnitude = -2.5log10 I K And I = I0/d^2 So in terms of I0... Apparent Magnitude = -2.5log10 (I0/d^2) And the Stefan-Boltzmann law says: Energy Flux = Sigma(T^4) In my reading it says that Intensity is the energy emitted per unit of area per unit of time. It says the same...
  30. Kate_C

    B Question re binary star systems & possible orbits

    From what I gather, there are S-type, P-type & T-type systems, but I'm having a hard time wrapping my mind around the orbital possibilities. Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the...
  31. T

    B Star Photography: Can We See Stars as Disks?

    Has the telescopes gotten good enough to photograph an actual disk of any star? Or are they all just points of light? tex
  32. mollwollfumble

    B Would lightning be possible on brown dwarfs?

    Lightning is well known from planets, and to some extent the bigger the planet, the more powerful the lightning. Would it also be possible on brown dwarfs (Y, T, L, M)? What about red dwarfs (M)? Other stars?
  33. phinds

    I Discover the Rare Black Neutron Star

    This BBC article posts no references so I wonder if anyone has any idea how significant it is? https://www.bbc.com/news/science-environment-53151106
  34. T

    I What happens when a Neutron Star forms a Black Hole?

    Supposing the total mass of a stationary, non rotating Neutron Star is just one Kg below the mass required to form a black hole. Based on the wiki reference below the Schwarzschild radius must be just beneath the surface of the Neutron Star sphere. Now supposing an object with a mass of one Kg...
  35. E

    New Star Wars film "announced"....

    https://www.bbc.co.uk/news/entertainment-arts-52535428 Pretty exciting news, I thought Taika's episode of the Mandalorian was the best of the bunch and the other films of his that I've seen (Thor Ragnarok/Jojo Rabbit) are pretty solid. Any ideas as to when it might be set? There was talk of...
  36. R

    How Do You Apply Conservation of Angular Momentum to a Collapsing Star?

    For part a I know the conservation of angular momentum is used, but I am not sure how to formulate the equation from the information given in the problem. I know that after the equation has been set up you set it up to solve what Rf is. For part be isn't the finial and initial rotational kinetic...
  37. F

    A Can a single star with 6 to 8 solar masses end up as a supernova 1a?

    Can a single star with 6 to 8 solar masses end up as a supernova 1 (having a remnant mass slightly above the Chandrasekhar limit) and being completely disrupted? This idea is presented by John Gribbin in his books “Stardust” and “The Universe”, but I can’t find any other reference or source...
  38. T

    B What is the Cooling Time of a Neutron Star?

    Neutron stars have surface temperatures of 1,000,000 degrees K. Yet they are not creating energy like a normal star. They are just cooling off. How long does it take for such a star to cool to room temperature, 300 degrees K.?
  39. tanaygupta2000

    How Do You Calculate Particle Density in a Star Using Electron Energy?

    I am confused whether for electron I have to use rest mass energy (moc2 + 0.8 MeV) or just 0.8 Mev for calculating E. Also how do I find minimum density of a neutron star using above data ? Please help !
  40. Attu

    B Neutron Star Paradox: Understanding Coulomb & Gravitational Forces

    For instance let's take that a neutron star mass is so high that the gravitational force is more than the coulumb force. If this happens then then the electrons will go down and alpha particle will be left . This is not observed in the star so how will the particle stay normal By the way I am...
  41. tanaygupta2000

    Degeneracy pressure of a White Dwarf Star

    So far, I am provided with all the required values for calculation, except N. If N = total number of electrons in star, then using N = mass of star/ mass of an electron should be no problem. Am I right?
  42. K

    I The life cycle of a star and the bell shaped energy emission curve

    Do all stars in their life cycle (t) emit energy (E) that follow a bell shape curve? If yes, is the curve symmetrical always? How is this related to nuclear and thermal time scale?
  43. S

    I This Wikipedia article about Scholz's Star doesn't make sense

    I was reading this article @ Medium, which shows our Neanderthal (3K or so times removed) cousin looking at Scholz's Star: And then the Wikipedia article about it https://en.wikipedia.org/wiki/Scholz's_Star which says: Prehistoric folks most certainly did NOT have access to telescopes...
  44. M

    Some hypothetical limits for the Star Wars universe?

    I’ve read many Legends and Canon Star Wars books and I always take away stuff on their limits of technology and science. Over the years; here are some things they said science can’t do. 1.) Cybernetic liver- In Lost Stars, it was said Ciena’s liver could not be replaced as it was one of the...
  45. S

    I What force potential should I use for star formations?

    I'm running some molecular dynamic simulations and I came across this, https://en.wikipedia.org/wiki/Star_formation#Cloud_collapse , and I was wondering if there was a specific force potential to use in this case. Supposing I have a ensemble of heated atoms moving around and I cool them down...
  46. S

    Star Trek: Picard -- anyone seen it yet?

    Hi everyone! I had the opportunity to see the series premiere of Star Trek: Picard and really liked it. As a long-time fan of TNG it was a great episode re-introducing us to Picard, and can't wait until the next episode is available. I was wondering how many of you here on PF has seen it.
  47. K

    I How is the information of a change in position of a star transmitted?

    Gravity is the curvature of space time. Stars move relative to each other. How is the information of this change transmitted through spacetime? I have just finished reading "Reality is not what it seems - The journey to quantum gravity" by Carlo Rovelli. (Can the content of a book be discussed...
  48. A

    I Help with the color of a star cluster

    I am working on a problem which asks for the B-V magnitude of a star cluster given N stars of type F and M stars of type K. I have values for B-V for both stellar types. I've derived a general formula for computing the magnitude of the cluster from the magnitudes of each star type, which...
  49. DennisN

    Star Wars Episode 9 - The Rise of Skywalker (Spoiler thread)

    WARNING! This thread contains spoilers for Star Wars: The Rise of Skywalker. If you have not yet seen the movie, we strongly encourage you to turn around and return once you have. Please use this thread for discussions about The Last Jedi, including spoilers. :smile:
  50. MeteoriteChina

    B Is this a star before it hit the ground on Earth?

    hi guys, I have a rock, I think its a complete star or maybe core meteorite, what do you think about it? It was found a few months ago in mountains in Shandong Province in China. desc: composition：Nickel iron diameter: 4cm weight:264g Regards Leonard
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