What is Stars: Definition and 890 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. T

    B Measuring distance between two stars in a binary system

    Hello I am trying to teach myself some basic maths for astronomy from a book, namely trying to calculate the distance between two stars in a binary system. One thing i am confused with is what angular separation means and how it can be translated to true physical distance between them using...
  2. jedishrfu

    B There's Gold in Them Neutron Stars - or - Maybe Not

    https://www.sciencealert.com/neutron-star-collisions-may-not-be-making-much-gold-after-all
  3. T

    B Why is an inverse logarithmic scale chosen for the magnitudes of stars?

    Star magnitudes of brightness seem to use inverse logarithmic scales, is there a benefit to this? Why was this chosen, i can understand logarithmic might make it easier to interpret data in same way we do similar for earthquakes etc. But why inverse ? When i look at a HR diagram for example (...
  4. LCSphysicist

    Differents ways of ordering bars and stars

    Actually, the answer is But i am not sure why we can apply combination here. I am a little confused. I could get the answer fixing the bar 1 in each place, with this fixed, we could change the position of the other bar. That would be: First we have 7 different position After this, 6 different...
  5. D

    I Remains of collapsed stars as touching binary planets?

    Would it be in any way physically possible for a binary star system to evaporate / explode, leaving behind two spheres of a solid metal such as gold (or an alloy), which were then rigid enough to drift together and maintain their shapes, rather than just collapsing into a larger sphere? And...
  6. AN630078

    Intensity of Stars and the Inverse Square Law Problem

    1. speed of light = 3*10^8 ms^-1 length of an Earth year=365 days*24 hours*60minutes*60seconds=3.15*1 0^7 seconds distance=speed*time 1 light year= 3*10^8 *3.15*10^7=9.46*10^15m 4.2 light years = 4.2*9.46*10^15m=3.9732*10^16m ~ 3.97*10^16m (to 3sf) 2. Intensity=power/area Power=1.4MW=1,400,000...
  7. I

    B Why certain stars seem to move very little in the sky

    Why is it that some celestial bodies when observed from the Earth appear to move very little in the the sky throughout the seasons, even though the Earth in the meantime has traveled millions of miles in its orbit around the sun? From my location in Montreal, Canada, there are only very few...
  8. M

    B By what process do different sized stars form?

    So the standard explanation for star formation says we have a disk of gas collapsing into itself until a certain pressure/temperature is reached at which point the star "ignites" and pushes away the rest of the material in the disk. My thinking is, surely this pressure/temperature needed for...
  9. K

    I Exploring the Quark Stars: Hexaquarks and Proton Decay

    Question: Is it believed a "quark star" exists within all neutron stars, or just heavier neutron stars. Do protons actually decay under this pressure (quark soup)? Are Hexaquark bosons able to remain stable beyond the limit of a proton, or would they decay at the same time of a regular...
  10. Kayla Martin

    Why is the degeneracy criterion the same for all stars?

    Is it anything to do with the equation being independent of mass etc.. of the star? or to do with the Pauli exclusion principle? Any help will be much appreciated.
  11. A

    What is Causing the Zig Zagging of Stars in the Night Sky?

    At midnight on may 12 2020 I saw what at first I thought was a drone zig zagging around in one spot in the sky. I looked outside at it again about ten minutes later it was doing the same thing in the same general area. I also noticed another star doing the same thing in a different part of the...
  12. S

    I What stars were observed @ 1919 solar eclipse to prove relativity?

    Was there a published report of exactly which stars which were supposed to be at position A but were observed at position B, etc.?
  13. Leonardo Muzzi

    I Why the center of black holes should be different from neutron stars?

    Physically speaking, why the insides of the least massive black hole should be any different from the heaviest possible neutron star?
  14. K

    I Will anti-parallel light beams between two stars stay parallel?

    In our galaxy, two stars, A and B, move about 20 km/s in slightly different directions to each other. The stars are about 15 light years apart. Initially, the light beams are exactly anti-parallel. Will light beams emitted from star A traveling towards light beams emitted from star B stay...
  15. H

    I Does the expansion of the Universe heat stars and bodies?

    The expansion of space is about 68 km/s/Mpc, or 0.00002 km/s/light year. The radius of the sun is about 700000 km. Thus, initially ignoring additional forces, the change in radius of the sun due to the expansion of space is about 1.5*10^-9 m/sec, or 5 cm/year. I assume that this expansion is...
  16. patrykh18

    Numerically simulating stellar pulsation using a "one zone" model

    The question is taken from An Introduction to Modern Astrophysics by Carroll and Ostlie. I did manage to do the entire question and plot the relevant graphs but I just want to to investigate a bit more. For example I want to look at how the graph would like in the case of the Sun. I don't know...
  17. pinball1970

    Jim Al Kalili Darwin day lecture: written in the stars

    Darwin day lecture: written in the stars: How to live happily in a deterministic universe. University of Manchester 31.1.20 Did anyone from pf attend? Or has seen him discuss this topic? Anyone interested in this topic? Too philosophical? There is a summary on his blog here...
  18. Anand Sivaram

    I Viewing Planets or stars from a high altitude

    We can not see planets or stars during the day time because of the scattering of the sunlight. But, in space, all planets and stars would be visible. Consider the situation that a rocket is going to space during the day time. At what altitude these stars or planets would become visible? On...
  19. L

    B Colliding Neutron Stars Collapse into Black Holes

    Here is a presentation on the discovery of two colliding neutron stars and the resulting phenomena such as gravity waves, gamma ray bursts, and synthesis of high atomic number elements. The author is a theoretical physicist who is involved in the research. He says that the neutron stars most...
  20. miafrasca_

    B High school Astrophysics Research Project Suggestions Please

    Hi, so I'm currently a senior high school student and I'm doing a research project on Astrophysics. I just need help on picking a topic as I know there is a lot out there. I need a project idea that is current but not too challenging as I am limited with resources. Thanks.
  21. M

    B Can neutron stars lose energy?

    Since electromagnetic radiation is emitted as electrons decay from higher to lower states of excitation, I would assume that neutron stars cannot lose energy by blackbody radiation. That would leave tidal drag and evaporation as the only ways a neutron star can lose energy...True?
  22. O

    B Will Big Stars Turn Into Red Supergiants or Red Giants?

    Hey. Medium sized stars will turn into red giants. What about big sized stars? As far as I know they will turn into red SUPERgiants. But, will they pass through a red giant phase before it happens? In conclusion, will a big star turn firstly into a red giant and secondly into a red supergiant...
  23. A

    I Why is there a difference between the composition of planets and stars?

    I've been thinking about this from time to time, I'll try to make this short and understandable. So we go back to the early universe within our current best model of extrapolation called the Big bang theory. In the early universe as it was expanding we have a very dense and energetic matter...
  24. T

    I Mass-luminosity relationship for red giants and AGB stars?

    Hello! I'm attempting to find the mass of a red giant and an AGB star. I have their luminosities, radii, and the masses of their cores. I'm looking for some kind of mass-luminosity relationship. Do you know of any, or do you know of a good place to look for such equations? Thanks!
  25. P

    I Proton & Electron Speed in Stars: What You Need to Know

    How fast are protons and electrons moving within a star?
  26. H

    Stars: Light from the Past, End in Sight?

    If the light we are viewing while looking at the stars has left the origin(guess) billions of years ago. So I propose, maybe not in anyone's lifetime the end of the transmission is following the light we are absorbing today. Is that a standing wave buffered, however variable with an end if we...
  27. Z

    I What causes the mysterious eclipses in Epsilon Aurigae?

    The closest star tp the sun is 4 light years away. Are there any stars that are closer that are not part of a multi=star system? How close close can stars get to each other and still be independent systems?
  28. K

    B Intensity of Spherical Shell of Stars

    Given that L is the luminosity of a single star and there are n stars evenly distributed throughout this thin spherical shell of radius r with thickness dr, what is the total intensity from this shell of stars? My calculations were as follows: Intensity is the power per unit area per steradian...
  29. Cerenkov

    B What are the maximum masses of White Dwarves and of Neutron stars?

    Hello. I'm very interested to find out more about the maximum masses of white dwarf stars and of neutron stars. Please note that while my level in this forum is Basic, I am familiar with the role that the Chandrasekhar limit has played in our understanding of white dwarves. I was therefore...
  30. B

    B Age of the Universe vs Age of the Stars

    Recently a news article stated objects found in the universe have different ages, could it be that our universe is inside an already existing universe and that is why it is able to expand so easily.
  31. A

    Estimating the mass of our galaxy, and the number of stars in our galaxy

    A previous thread outlined the problem with a correct answer, however I don't understand where they got the formulas from. Here are the steps I've taken so far: 1. Convert 2*10^8 years to seconds = 6.3072*10^15 seconds (period,T) 2. The previous thread then went on to say you plug period and...
  32. MathematicalPhysicist

    I Planets or stars that are composed entirely out from Dark Matter.

    Is there a possibility that there are stars and planets that are composed entirely of DM? How would we detect such stars or planets? Well, I am not sure about stars, as the definition of a star depends on its fuel that it uses, I guess.
  33. T

    Binary System in circular orbit: Separation distance between stars

    Distance is d=1/0.07 = 14.3 parsecs The Doppler shift of one star is, Δλ = 512 - 512.04 = -0.04 So the radical of the velocity of the star is = (-0.04/512) x (3.00 x 10^5 km/s) = 23.4km/s which is the same for both stars because they have the same mass. This is as far as I've got.
  34. S

    B Why do pictures of stars have 4 cardinal points?

    I've noticed that a lot of these pictures are like this. Is it something to do with the error in the machining of the lenses?
  35. A

    B Red Dwarf Stars - Planet Habitability around "Flare Stars"

    I've been doing some thinking on a sci-fi story about a colony around a Red Dwarf Star. I understand that most planets around Red Dwarf Stars, at least in the habitable zone, would be tidally locked. I created another thread to ask about ways to maintain a planetary rotation. My main question...
  36. A

    B Question about Preventing Tidal Locking around Red Dwarf Stars

    All, A couple of questions about planets around Red Dwarf Stars: I'm imagining a planet around a Red Dwarf Star...think Trappist-1...and want to know how I can prevent tidal locking for an Earth-sized terrestrial planet in such a star's habitable zone...say, 1/50th to 1/20th of an AU from the...
  37. C

    About initial mass function and mean mass in stellar cluster

    Homework Statement Assuming a Salpeter IMF with upper and lower mass limits of 0.1 and 20 M⊙ respectively, calculate: (i) the mass point at which half the mass formed in a stellar cluster lies in more massive systems and half in less massive systems. ii) the mass point at which half the...
  38. X

    B Convection in Stars: The Role of Mass and Structure in Fuel Consumption

    As most people know, massive stars such as blue giant of Wolf-Rayet stars are short lived,only for a few million years.well tiny stars such as red dwarfs seems to be immortal by human’s prospective, and indeed they can live up to a trillion years! Most people thought it was only caused by the...
  39. James Beedy

    Comparing image sizes of the hotter stars with the cooler stars

    Homework Statement When comparing image sizes of the hotter stars with the cooler stars, do hotter stars consistently appear larger in one image and cooler stars consistently appear smaller in the other image? Why or why not? Homework Equations Stellar Spectra Classification[/B]The Attempt...
  40. W

    B The unusual motion of stars in galaxies

    Ive been lying in bed this morning wondering about the unusual motion of stars in galaxies.The whole disc rotating like a record at the same speed.Does it mean that the effects of gravity are simply altered by speed?Much like a wonder-wall.So the faster the speed of the object,or stars,the less...
  41. JulioHC

    Derivation of blackbody radiation equations for stars

    Good evening, As part of my course, I had this week two lectures about the blackbody radiation and its relation to the stars. While I do understand how to use results such as the Stefan-Boltzmann law and Wien's Law I'm lost in other parts. I think the only parts that I don't understand yet are...
  42. nmsurobert

    I Spectral Class of Stars: Exploring Electron Transitions and Absorption Spectra

    I understand the process of electron transitions but I don't understand how or why these pictures are put together. If we're looking at the spectra of a star, why are this pictures shown as absorption spectra and not emission?
  43. Michaela SJ

    B Further collapse of Neutron Stars

    First post and I am not a scientist - just a curious soul. What stops a neutron star/magnetar from collapsing further into a black hole?
  44. F

    B Why most stars seem to rotate the same direction in a galaxy?

    After much questioning and soul-searching I got my answers of why galaxies rotate, and for that I greatly thank the gurus in the forum (so I'll not forget: conservation of initial angular momentum, non-isotropic material scattering, slowdown of infalling materials and non-isotropic infalling of...
  45. N

    I Why do stars only produce up to iron and nickel

    I know it's a common question but I've found no answers online so far. My professor has made a point out of saying that fusion reactions after iron and nickel do release energy but just not enough to keep the star from imploding. This didn't make sense to me. How would fission release energy if...
  46. bbbl67

    I Were Population III stars powered entirely by p-p fusion?

    In modern stars, the more massive a star is, the more likely that it is powered by the CNO fusion cycle, where Carbon, Nitrogen, an Oxygen act as catalysts for creating helium from hydrogen. In stars over 1.3 solar masses, this is the primary fusion process. Below that that level it's a mix of...
  47. C

    MHB How Can I Understand and Use the Stars and Bars Selection Formula?

    Hey. I find it difficult to understand the logic and the appropriate usage of the formula: $\dbinom{N+K-1}{N}$ I don't really understand what's posed behind the scenes of that one. So I have some example for an exercise which requires the usage of this formula, but I know only to substitute...
  48. DracoMalfoy

    Power and temperature of stars

    Homework Statement Star 1 emits energy at a rate that is 2 times that of Star 2. If Star 1 also has a radius that is 3 times larger than Star 2, how do the temperatures of the stars compare? a. Star 1's temperature is 2.58 that of Star 2. b. Star 1's temperature is 3.75 that of Star 2. c...
  49. N

    I Measuring Star Radii with General Relativity

    Hi, I'm wondering if it is possible to measure radii of stars using general relativity, given its explanation of gravity as curvature of space. Thank you
  50. F

    I Correlation between a Star's Luminosity and Distance?

    I made three charts from several different sources plotting the luminosity and distance from Earth of 26 to 300 Stars. In each chart, there appears to be a correlation between a star's luminosity (in solar units) and its distance from Earth (or solar system, whichever you prefer) in light years...
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