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. U

    B Bose Stars (dark matter in origin)

    https://www.sciencealert.com/matehmatical-model-of-cold-dark-matter-bose-einstein-condensate-stars Interesting read. Thoughts and comments?
  2. W

    I The Shape of Very Massive Stars: Spheres or Something Else?

    What is the shape of very massive stars? Are they simply spheres or something else?
  3. Simon Peach

    B Why is the gravity of a neutron star stronger than that of its original star?

    I've just watched a vid about jets of matter and neutron stars. It was stated in it that a neutron star is a star that's been compressed from say a sun sized star to the size of a city, every thing OK upto now. Then it goes on to say that it has, the neutron star, enormous gravity, this is were...
  4. Spinnor

    B Galactic Collision Creates a Ring of Black Holes and Neutron Stars....

    From, https://www.syfy.com/syfywire/wham-bullseye-galactic-collision-creates-a-ring-of-black-holes-and-neutron-stars ..."“So you have a nice, normal spiral galaxy, right, just out there doing its thing, when BAM! A smaller galaxy careens right through the middle of it like a bullet! Chaos...
  5. Leonardo Machado

    I Neutron Stars mass and radii observation data

    Hello everyone. I'm currently working on NS mass relations and trying to plot a curve with predicted masses-radii and observations on NS. There are some free data at this website: http://xtreme.as.arizona.edu/NeutronStars/index.php/neutron-star-radii/ . I downloaded the .tar file and tried to...
  6. YoungPhysicist

    I Is the Sun a Perfect Black Body? Investigating the Reflection of Radiation

    Black bodies are objects that don't reflect radiation. But If I shoot light beams to the sun, it doesn't reflect it , so does that mean the sun is a black body(or at least very close to a theoretical one)?
  7. J

    I Why don't red dwarf stars emit white light like the Sun?

    Blackbody radiation spectra of hot light sources ( stars in this case) should have the full visible light spectrum and still stars less massive than the Sun emit reddish light while stars more massive than the Sun emit blue light. How is the blackbody radiation spectrum altered by the star mass?
  8. Felipe Lincoln

    Newton's law and double stars moving in circles

    Homework Statement The two components of a double star are observed to move in circles of radii ##r_1## and ##r_2##. What is the ratio of their masses? (Hint: Write down their accelerations in terms of the angular velocity of rotation ##\omega##) Homework Equations ##m\ddot{\vec{x}}=...
  9. T

    B Why don't high mass stars expand and cool?

    When a high mass star starts to fuse heavier elements, the core heats up the outer layers enough to for them to begin fusion of their own. My question is: because the star hasn't gained any mass, but it has increased in temperature a lot, why doesn't the star expand and cool like a red giant...
  10. S

    I Exploring the Hot Corona Phenomenon in Stars Beyond G2 on the Main Sequence

    We know that solar corona is heated up although we don't know yet the mechanism. I was wondering which other type of stars, else than G2, in the main sequence suffer of the same effect? Thank you!
  11. sjp9220

    I Why are there so many different kinds of stars?

    There are red giants, blue giants. white dwarfs, red dwarfs, brown dwarfs, etc., etc., etc,... Why? do they have different chemistries? Are they each at different stages in their lives? Is there a combination of reasons?
  12. T

    Combined magnitudes of two solar-type stars

    I am having a issue with part a) of this question, I am not entirely sure if what I am saying is correct, could somone if possible check my logic 1. Homework Statement Two solar type stars (all physical properties are the same as for the Sun) are in a close binary system. Each individual star...
  13. E

    I 2 second delay at the merger of two neutron stars in August 2017

    Some new papers appeared about processes in the collision of the two neutron stars, measured in August 2017. Is now more clear, why 2 second delay between gamma rays and gravitational waves happens?
  14. Z

    I How do we get stars so much more massive than the Sun?

    When a cloud of gas reaches a critical density, thermonuclear reaction occurs and a star is born. all other gas is blown away by the staller wind. So how do we get stars so much more massive then the sun?
  15. Sophrosyne

    B Spectroscopy of Stars: Electrons in Plasma

    Astronomers can determine the presence various elements in a star through spectroscopy of the incoming light from that star. The characteristic spectral lines of each element are formed by electrons transitioning between the various orbital energy levels around the nucleus of their atom. But...
  16. S

    How do we know that light that comes from the stars is in past?

    So for some reason, from time to time, i always come back to this question and i can't remember that part of the physics while i was studying and most of the explanation are pretty generic. Basically how do we know that light actually travels and not just oscillate and transfer energy when...
  17. A Alex P

    I Are Stars and Planets Differentiated by Nuclear Processes in the Solar System?

    In solar system, we have sun and planets revolving around it. We have satellites orbiting around some of planets. Are all of these are same thing, just differentiated on the basis of size and nuclear processes occurring inside them? I mean, if nuclear processes occurring inside their core its a...
  18. nmsurobert

    I How Does the GAIA Program Count 1.7 Billion Stars in Its Image?

    I just an read article on the ESAs Gaia program. I was wondering how they count the 1.7 billion stars in the image? Are the stars cataloged as the images are taken? Or is there a method that is used after the images have been collected? http://sci.esa.int/gaia/60169-gaia-s-sky-in-colour/
  19. BL4CKB0X97

    B Number of stars in the universe over time

    Hello.Long time,No See. I am just wondering if anyone can point be in the correct direction. Preferably with a link or a book that I should read as i would like to understand, not just know the answer. I am just wondering how much the number of stars in the universe has changed over time...
  20. EF17xx

    Understanding Perfectly Black Bodies

    Hi! I'm trying to understand a perfectly black body. So the definition I have found is that a black body is one that absorbs radiation of ALL wavelengths and reflects NONE. Therefore it appears black at low temperatures. And when heated it emits radiation of all wavelengths making it appear...
  21. mjda

    I Why Is Convection Efficient in the Outer Layers of Stars?

    I'm trying to understand why convection is an efficient mode of energy transport in the outer layers of the solar interior. Could anyone give me a little bit of knowledge? Thank you!
  22. mjda

    I Stellar Thermal Energy with no Nuclear source

    Can anyone enlighten me as to why the total thermal energy of a star will increase with time if the star has no nuclear energy source?
  23. M

    I How do we measure the velocity of stars in a galaxy?

    I have read somewhere that the parallax method can be used to measure the distance to stars up to 400 light years away. I did a quick calculation and estimated that it means that our telescopes can resolve an angular movement of 8.15x10-3 arc seconds. Taking the distance between the sun and the...
  24. Leonardo Machado

    I Standard Solar Model: Learn About Its Complexity

    Hi everyone. I'm looking for a good book or some good source of informations about the stantard solar models, but i can only find compact stars stuff. Do you guys have any sugestions ?
  25. BillTre

    A Plan to Make Artificial Shooting Stars

    A Japanese company wants to use a satellite to make shooting stars in 2020 for the Olympics in Japan. Later for the world.
  26. Harsha Avinash Tanti

    I The Role of magnetic field during the formation of small to medium scale stars

    Hi, I would like to raise a question about Role of magnetic field while formation of small to medium scale stars emerging from nebula ?
  27. A

    Binary system of stars (##\alpha## - centauri)

    Homework Statement ##\alpha##-Centuary is in a binary visual system with another star. Their separation, from their CM, is 8.0'' and 9.7''. The distance from the Earth is 1.31pc. Their revolution period around the CM is 80.1 years. I have to find masses and luminosities for each star. Homework...
  28. W

    I Would you see stars on the early Earth?

    Im wondering what the night sky would look like if you stood on the surface of the Earth as it was forming? Here is my best guess, I would like to know if I am on the right track 1. After it cooled down, it had no atmosphere so it would be like the surface of the moon so the stars wouldn't...
  29. B

    I Universe's First Stars Interaction with Dark Matter

    https://www.space.com/39837-first-stars-universe-fingerprints-dark-matter.html...
  30. heavystray

    B Why does Tc & Teff Differ for Different Types of Stars?

    I have a question regarding the results of my Physics investigation on Tc and Teff of stars. I found that the colour temperature that I calculated is significantly higher than the Teff for O and B stars. For mid temp stars, Tc is still more than Teff but the difference in small. But for cooler...
  31. J

    Which Letter Represents a Star Similar to the Sun Based on Emission Spectra?

    Homework Statement [/B] The top spectrum shows part of the Sun's spectrum. State and explain which letter best represents the light from a star that is similar to the Sun. Homework Equations None. The Attempt at a Solution I originally was thinking A but my book says B but only gives...
  32. Assaltwaffle

    I Star Gravitational Binding Energy Questions

    Hello everyone! I am a moderator over at the VS Battles Wiki, and I have some questions I believe one of y'all can answer. Basically the question is: how much energy does it take to destroy a star? We find this with GBE, but I have some questions as to calculating this value. As far as I am...
  33. wolram

    B If Quark stars exist why do Neutron stars become Black holes?

    From Wikipedia: Quark-degenerate matter may occur in the cores of neutron stars, depending on the equations of state of neutron-degenerate matter. It may also occur in hypothetical quark stars, formed by the collapse of objects above the Tolman–Oppenheimer–Volkoff mass limit for...
  34. D

    B Gravastar vs. Neutron Stars: A New Theory for Black Hole Formation?

    Has anyone else heard of that gravity waves may be the result of another type of supernova remains, called a Grav-Star? It seems almost to physically mimic a neuron star but stopped just shy of becoming a black hole, yet it still has enough of a gravity well to prevent light from escaping. Is...
  35. nmsurobert

    I Are Stars Absorbing and Re-Emitting Radiation from Space?

    Ive been reading about it for a while and I'm still confused. i understand that a star is not a perfect blackbody. but do stars absorb radiation from space and then re-emit that energy into space?
  36. G

    Why do neutron stars have such powerful magnetic fields?

    The sources I've looked at claim the magnetic field is present because there are still some electrons in the neutron star. Here is how I understand their reasoning: a star's radius significantly decreases when it collapses into a neutron star, ultimately decreasing its moment of inertia. In...
  37. shihab-kol

    B Sun's Expansion: Why Inner Planets Will Be Affected

    I read in some books that as the sun approaches the end of the fusion process(the complete one) , it will expand and engulf some of the inner planets. But why will it expand?
  38. J

    I Determining Mass & Info of Merging Neutron Stars from LIGO Signal

    How does one determine/calculate the masses, orbital period, and separation of two merging neutron stars from the characteristics of its gravity wave LIGO signal? And how does this information allow one to calculate the distance to the galaxy that housed the merger? And how can one calculate...
  39. A

    I Can a supernova produce multiple stars?

    Can a supernova produce some number of stars after it explodes or will it always produce just one, single star? Can the matter it ejects form multiple stars and solar systems or will there always be just one new star and its only new solar system?
  40. Guilherme Franco

    A Are period 5 elements common in most stars?

    My question might seem simple, however I couldn't find data on this. Let me explain my situation: I'm involved in a project about the formulation of new criteria to avaliate exoplanetary systems for search of extraterrestrial intelligence. The key question is mostly around the element...
  41. S

    I Actual number of stars in the Milky Way

    I hear wild varying estimates of how many stars there are in the Milky Way Galaxy, from 200 billion to 400 billion. Is the number closer to 200 billion or closer to 400 billion? What methods are being employed (other than GAIA) in order to count them?
  42. A

    Question about the radiation around Neutron Stars or Pulsars

    I have a sci-fi idea regarding being able to move planets around like billiard balls. I'm theorizing that, after a nova, some of the bands of material around a star formed a new ring of rocky planets around a Neutron Star. Naturally, these are bathed in radiation. Having never taken high...
  43. C

    Stargazing Looking for a beginner's telescope....

    Hi there, I love physics and I'd like to begin a bit of astronomy. I want to invest in a beginners telescope but I haven't a clue about what to buy. Some that I'm looking at are linked here: https://www.amazon.com/dp/B00XQMLA7Q/?tag=pfamazon01-20...
  44. davidge

    B Collision of Stars: How Often & How Many?

    How frequently is collision of stars in galaxies? If there are 100 bi galaxies and 100 bi stars each, then how many collisions should we expect in within, say, 1 year?
  45. wolram

    B Understanding Boson Stars as Potential Dark Matter Candidates

    Boson stars seem to be a good fit for Dark Matter. https://arxiv.org/pdf/1704.05057v1.pdf Can you help me understand why such a huge particle with such low mass can exist, and how it could be found experimentally.
  46. J

    B Black holes cause neutron fusion in neutron stars

    I read an article today stating that the possible explanation for the near total absence of heavier elements such as gold and uranium in many galaxies may be due to those galaxies not forming around a central black hole that has in absorbing one or more neutron stars causing fusion of neutrons...
  47. E

    B Ball Lightning and Stars: Unveiling the Spectral Similarities

    Has the spectrum of a ball lightning ever been photographed? If so, does the spectrum look like the spectrum of any star? Could one say: the ball lightning is the smallest existing star?
  48. Vanadium 50

    I Merging Neutron Stars: What We Know So Far

    Rumors are starting to fly that LIGO/VIRGO sees a signal of merging neutron stars, with an optical counterpart. Indeed, the thing that seems to have triggered the rumors was having a number of telescopes suddenly pointing at the same patch of sky. It's difficult to discuss the science behind...
  49. Ethan Singer

    I What causes pressure in White Dwarfs and Neutron Stars?

    Before today, I'd been led to believe that collections of only one (or few) types of matter could never exist: And to my surprise it is indeed possible to have degenerate matter, resulting from the death of less massive stars! So I'm curious: If these lesser massive stars collapse due to their...
  50. K

    Solve Stellar Ionisation Homework: Type O Stars

    Homework Statement Hi, I am studying for a test on Monday and I was wondering if someone could clarify something in my notes on the ionisation rate of Type O stars. The line in my notes says; L = 105L0 ⇒ S* ~ 105 /13.6eV ⇒ S* ~ 1049 Basically, I don't have an actual formula for S* and I was...
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