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. Z

    How Do Scientists Estimate the Distance to Stars?

    Think about this, a photon travel through the universe, its path can be reflected by other objects, bended by gravity. Therefore the path would not be a straight line anymore. But very often from the TV science shows stating the distances to other stars are some some million light years. How...
  2. P

    Empirical establishing of Mass-Radius relation for stars

    Hello, I need to determine Mass-Radius relation for stars, as I prepare myslef to finish my study work. I know it's possible to evaluate it theoritically in the form - M~Rn, but I have to prove it using empirical, observational data. Making a M(R) relation diagram is indispensable so I have...
  3. E

    Exploring the Red Shift in Stars: Uncovering the Mysteries of Our Galaxy

    When I look at the stars in the sky with my undressed eye, they are blue. But pictures of stars taken by scientist always show them as red. Does this mean that the stars in our galaxy are fairly stationary and/or moving closer to earth? Will I find that most red shifts will be seen in stars...
  4. M

    Stars: Creation, destruction and impact on the universe

    Hi all, Doing a project for 1st year special topics physics module in university and we're thinking of doing the project on stars. Just wondering if anyone might know of any good literature on the sublject that we could look into as part of our research. We have until mid January to do the...
  5. D

    Can Hawking Radiation explain the immortality of neutron stars?

    If proton decay does not occur, are neutron stars immortal? I was hearing that that was the case.
  6. K

    Why is the edge of the universe the place to look for the oldest stars?

    Forgive me if this has been covered already. If the universe has no center why do astronomers find the oldest stars at its edge? It seems to me that they should be everywhere.
  7. marcus

    Three times as many stars? (new estimate by van Dokkum and Conroy)

    The technical paper (published in Nature): http://arxiv.org/pdf/1009.5992v1 The NYT journalistic account: http://www.nytimes.com/2010/12/02/science/space/02star.html?_r=1&ref=science ==quote== How Many Stars? Three Times as Many as We Thought, Report Says By KENNETH CHANG Published: December...
  8. amarante

    Typical magnetic field in stars

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  9. M

    String stars instead of black holes?

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  10. J

    Help with gravitational potential energy of stars

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  11. M

    How High Can a Rocket Go Using Liquid Oxygen and Kerosene?

    Homework Statement A 20000kg spacecraft carrying 17000kg of fuel starts at the surface pf the earth, (Mass=6*1024kg, radius of 6.3*10^6 m). The liquid oxygen and kerosene rocket provides an exhaust velocity of 3500m/s. a.) How much high can the rocket go above the Earth's surface? b.)Once...
  12. S

    Taking picture of stars from weather balloon

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  13. D

    How can we see stars past 13.5 billion light years away?

    okay. i understand that stars can 46 million light years away despite the universe only being 13.5 billion years old. The universe is expanding. However what i dont' understand is how can we see a star that is say 20 billion lights years away if it takes 20 billion light years for the light to...
  14. S

    Formation of Stars: How Gas Spins to Fuel Birth

    If a typical star is created by a spinning ball of gas, how does the gas start spinning in the first place to fuel that birth?
  15. D

    Black holes giving birth to stars?

    Is it possible for a cloud of gass to condense around a black hole and for fusion to start? Or another way to ask. Is it possible for a star to have a black hole at it's center?
  16. D

    How Do Stars Achieve Their Massive Sizes?

    If Hydrogen fusion starts around 100JM (Jupiter Masses) then how do the larger stars get so massive? I was watching The Universe and it said some stars are over 200 solar masses and higher. How can a star get so massive?
  17. S

    Hypervelocity Stars: Exploring the Mysteries

    I'm not very good with words so if this seems redundant or not very well put together, know that i tried... I recently heard about white holes through an example of water from a faucet. The event horizon was a the ring of water that appears in the sink while the water is running. In the "even...
  18. russ_watters

    Mount Everest Review: No wifi, Rude Yeti = 2 stars

    http://www.cnngo.com/explorations/life/mount-everest-has-no-wi-fi-and-too-much-snow-014380?hpt=Sbin ...and homogenous views: snow, snow and more snow.
  19. R

    Curvature of spacetime inside of stars and planets

    hi, how does general relativity work INSIDE stars and planets, since the mass is no longer concentrated within a point, so there are necessarily gravitationnal effects outwards and not only inwards?
  20. P

    Pressure in stars from photons vs. electron/positron pairs

    In a recent popular science account of "pair instability" supernova, a statement was made, without explanation, that if fusion of oxygen started producing sufficiently energetic photons that most of them convert to electron positron pairs, the the outward pressure is drastically reduced and the...
  21. L

    Find the radii of the two stars

    Homework Statement From the light and velocity curves of an eclipsing, double-lined spectroscopic binary star system, it is determined that the orbital period is 3.15 yr, and the maximum radial velocities of stars A and B are 5.2 km s^-1 and 21.6 km s^-1, respectively. Furthermore, the time...
  22. L

    Calculate the masses of two binary stars

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  23. L

    Super black holes and stars orbiting them

    seen a programe about super black holes in which some stars where orbiting them . speeding up as they are slingshoted around them or whatever the proper term for this is . so why if the black hole is strong enough to pull them in the first place why do they not get pulled in completely ... what...
  24. R

    Hypervelocity stars and RX J0822-4300

    I was wondering what would be the gravitational force caused by stars with high speed. As an example, I was trying to compute the gravitational force exerted by RX J0822-4300. This radio-quiet neutron star has a radial velocity of 1500Km/s (i.e. 0.5% c). The thing is that I am not quite sure...
  25. nukeman

    Question about how stars appear to move westward?

    Ok, the stars appear to move westword correct? Is that because the Earth is moving eastword, so its just an illusion that the stars move westword? Is this Newtons 3rd law? (every action has an equal and opposite reaction)
  26. R

    Why do stars appear to be white in color?

    Why do stars appear to be white in color when viewed from the naked eye?
  27. M

    Distribution of stars in spiral galaxies

    I've been trying to locate an algorithm to model the distribution of stars in a spiral galaxy. Simple, I thought, I'll just Google it. However I quickly disappeared up my own black hole! What I'm looking for is a simplified algorithm I can use to model n stars in a galaxy of size x (for...
  28. S

    Are There Green Stars? Exploring Unusual Astronomic Colors

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  29. B

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  30. A

    Exploring the End of Stars: A Futuristic Novel Concept

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  31. N

    Wayward Stars: Has Ejection Ever Been Observed?

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  32. M

    Do stars actually exist beyond our solar system?

    It is a question i have been thinking about for a while. When we look into the sky, are we actually looking at other stars or are we looking at our own sun from lots of different angles, we know light bends with the gravitational pull of planets. is it not possible that the light we see from...
  33. Orion1

    R136a1: The Most Massive and Luminous Blue Hypergiant Star

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  34. V

    Are photons much older than stars?

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  35. TrickyDicky

    Dwarf Stars: Detecting Low-Mass Stars in the Universe

    How hard is it to detect stars say of a tenth the solar mass, I know it depends on the distance of course, but how frequently do we spot these kind of stars ,moreless?
  36. C

    Does electromagnetic radiation from pulsar stars

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  37. P

    Stars from outside the atmosphere

    Hi Guys .. I have a question and I hope I get a good and obvious answer PLZ .. How do stars and moon look like from outside the Earth's atmosphere ? If we went out of the atmosphere of the Earth , will we see the stars in the same way as we see them from .. here ? In other words do the...
  38. U

    When do neutron stars, supernovas, and pulsars form during a star's life?

    can anyone tell me about various stages of life of a star? when does a neutron star, supernova, pulsar form?
  39. T

    Eternal universe vs finite life of stars

    I heard on a recent podcast that most astronomers and physicists of the early 20 th century, if they thought about it at all, believed that the universe always existed, i. e. it had no beginning. Even Einstein accepted the Steady State Theory, along with many others. How did these astonomers...
  40. n.karthick

    How Do Astronomers Count the Number of Stars in the Sky?

    Hi I want to know how astronomers count the number of stars (or any other celestial object for that matter) in the sky. Will they take a photograph and do some signal processing like counting the number of brightest spots? Is it possible to count accurately since there are billions and...
  41. J

    Why is the ideal gas law a good approximation for stars?

    Any ideas appreciated!
  42. L

    For anyone who does not beleive in black holes, we what happens to neutron stars then

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  43. S

    What Happens to Starlight When Traveling Faster Than Light?

    If, for argument sake, you had a spaceship that could go thousands of times the speed of light what would happen to the electromagnetic radiation being emitted from the stars you head towards and away from? Would the stars that you are traveling towards get duller and duller the faster you go...
  44. T

    Why do neutron stars suck the gas from their companions?

    I always here about neutron stars and black holes sucking the gs from their companions. However, a star loses mass before it becomes a neutron star so I don't understand why it afects its neighbor more when it is a neutron star than when it was a regular star.
  45. N

    Why it is the goal to achieve 5 stars in something?

    Does anyone know why it is the goal to achieve 5 stars in something? Why not 3 or 6 or 9 or 358? I personally would have started the trend at getting 6 stars, being that it's a perfect number and all...
  46. menniandscience

    Why Don't Stars Expand with Space?

    Hi! my question is, if space expand, how come the stars (and planets) don't? they are part of the space and not "sitting inside" or somthing like that. meaning, the Earth should grown bigger all the time. you can think about marking a dot on a bloon, as you blow air inside the bloon starts...
  47. L

    Why stars blink and planets don't

    Why do starts blink and planets do not. There are some stars that are just as bright as a planet(unless my observation is wrong). I know the light from the star enters Earth's atmosphere and due to the variation in density(which means change in dielectric constant of the medium in which light...
  48. S

    Finding mass enclosed my a stars radius from center.

    [urgent] finding mass enclosed my a stars radius from center. Homework Statement the rotational speed of an orbiting object is given by v= (Gm/R)^1/2where R is distance at which the object is rotating from the center of the mass distribution and M is the amount of mass within the radius R...
  49. R

    Minimum distance between stars so we see them as two distinct stars

    Homework Statement Using a telescope with circular aperture of diameter 2.5 meters and wavelength 463 nm. The stars are 10E22 meters away from us. What does the distance between them have to be so we view them as two stars? Homework Equations angle = 1.22 x (wavelength/diameter) >...
  50. F

    Why are Stars Not Visible in Astronaut Photos?

    Ive noticed every time i see a picture of the ISS or astronauts working in outer space there is NEVER any visible stars? Why is this? i been told that they filter it somehow since they stars would be so bright, or is there another reason this has been on my mind for a long time
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