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. J

    Exploring the Proportionality of Luminosity & Mass in Stars

    Homework Statement Homework Equations L = M^3.5 The Attempt at a Solution Am I right in saying that this is the correct proportionality for luminosity and mass in a star? If it is, i am confused. In an example I have it states that when mass is doubled the luminosity...
  2. G

    Which Open Source SPH Code is Best for Simulating Mergers and Rotating Objects?

    I need so advise on SPH open source code to use to look at mergers and rotating objects... if anyone has some links or tutorials? Thank you!
  3. D

    Is the process of fusion really enough to keep stars from imploding?

    Hi, has it really been proven that the process of fusion is REALLY enough to keep stars from imploding under their own gravitational force? I suspect that there might possibly be another factor involved, in keeping the stars inflated until they start to cool and hit that point of...
  4. U

    Gravitation problem (estimate numbers of stars in our galaxy)

    Homework Statement The sun mass MS = 2.0 E30 kg revolves around the center of the milky way which has a total extension of 2.2 E20 m. The sun takes 2.5 E8 years to complete one revolution. Estimate the number of star in our galaxy based on this data. Suppose that the distribution is...
  5. A

    What do the stars look like from space?

    From the first few hits I found on the internet, here's what I gather: They are the same as they appear from Earth, except they do not twinkle (no atmosphere). They are like small points of light. The contrast between stars and black background sky is also greater than on Earth. They can...
  6. Evo

    How Have Rock Stars Changed Over the Years?

    I would not have recognized many of them. http://www.nbcsandiego.com/entertainment/music/NATLRock-Stars-Then-and-Now-97329329.html
  7. C

    How Can Mechanics and Sound Be Tied into a School Project on Stars?

    Hello all, new here, so I hope this would be the best forum for it to go into. Anyway, for school we have to do a project on any subject we want, and tie it into what we've been studying in physics. I selected stars, and I'm having a bit of trouble tying it into everything. What we've done so...
  8. R

    A question regarding the B-V measurements of stars

    I've been looking up some information regarding the Owl Nebula, in order to make some calculations of my own. I've only been able to find the V magnitude or the general magnitude of the nebula as a whole. Is there any way to find the B magnitude or the B-V measurement of the star, given what...
  9. R

    Do all stars have same revolving speed?

    In our milky way, do all stars have same revolving speed? This Question is in my mind because we always sees that all star are always in same position with respect to other, i mean if take an example of orion constellation then it seems that betalgeous is always in a same position with respect...
  10. Q

    Estimating number of Neutron Stars in a Star Cluster

    Homework Statement An open cluster is observed to contain 1000 stars. Clusters contain many more low mass stars compared to high mass stars, reflecting the star formation process. This depen- dence of the number of stars formed in a given mass range is expressed in the so-called initial mass...
  11. D

    Neutron stars not sustained by degeneracy force?

    I have just attended a talk, where the speaker (a professor in Hong Kong University) claims that neutron stars don't collapse due to "nuclear forces". He further explains that those nuclear forces are residual strong forces (i.e. exchange of pions). However, the mainstream saying (according to...
  12. A

    Density profile of Wolf Rayet stars

    I have been looking for the density profile ( density vs radial distance ) of a Wolf-Rayet star. Kindly suggest me some resources.
  13. A

    Exploring the Basics of Numerical Simulations for Modeling GRBs

    I intend to learn numerical simulations of collapsing stars. Could you suggest me some useful resources? i am familiar with matlab.
  14. S

    Massive Stars Spin Faster: The Reason Explained

    It is said that massive stars spin faster than less massive ones and I am always wondering why.Could someone please tell me the reason? Thanks a lot.
  15. L

    Does iron really kill fusion in stars?

    I've just watched the Extreme Stars program in How the Universe Works and it states that when a massive star starts to make iron, the fusion is quenched and the core collapses. From the program, it sounds like the process is fast and will happen when a few grams of iron is formed. I find this...
  16. T

    Can you see stars from the surface of a ringed planet?

    I am writing a novel set on a ringed planet. The plot calls for the rings to be about a thousand years young, more a torus of gas and dust and speeding moonlets. Would a person standing on the night side of this planet be able to see stars? Or would the rings scatter enough light from the sun...
  17. J

    Spectral Energy Distribution of T Tauri stars

    On page 5 of the link http://www.maths.qmul.ac.uk/~rpn/ASTM735/Week9-powerpoint.pdf , there are 2 graphs. I'm referring to the 2nd graph (the one with the flared disk fit). What is the green plot supposed to represent?
  18. J

    Question on how stars are located

    Just a thought - does the universe have the equal of a refractive index so to speak, to measure where stars are, due to gravity curving spacetime. thanks
  19. E

    How does diffraction affect telescope magnification?

    Homework Statement Vague class discussion. Stars are points and a telescope does not magnify them. How then can more stars be seen with a telescope? Homework Equations I know magnification for a telescope is fo/fe but that is not much help The Attempt at a Solution Is it because...
  20. I

    Evoltuion of Magnetic Fields in Neutron Stars

    I have been reading research papers on this topic, such as Evolution of the magnetic field in magnetars J. Braithwaite and H. C. Spruit 2006 http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361:20041981&Itemid=129 This is informative but takes the...
  21. V

    How to use S-metric to periastron precession of binary stars

    The Schwarzschild metric allows to calculate the precession of an elliptic orbit of a particle around a large central mass, provided the mass of the particle is much smaller than the central mass M. This condition is not met in the case of binary stars m1 and m2 revolving around each other...
  22. L

    Celestial sphere and visible stars

    OK, maybe this is a silly question but, if you look at the sky in a program like Stellarium say, and then look north, why can you see stars at points on the celestial sphere corresponding to points on the other side of Earth from where you are? I hope this question is clear, what I mean is the...
  23. C

    Strength of materials - neutron stars

    I have a scientific background in materials science. However this is one type of material that we don't exactly learn about! Let's say you have a neutron star approaching a comparable mass black hole. As the neutron star approaches the event horizon for such a comparable black hole, tidal...
  24. H

    Binary stars ,time period of orbit?

    Homework Statement A binary system consists of two stars of equal mass m orbiting each other in a circular orbit under the influence of gravitational forces. The period of the orbit is τ . At t = 0, the motion is stopped and the stars are allowed to fall towards each other. After what time t...
  25. P

    Would you Hear a Stars Nuclear reactions if you were close to it?

    Would you "Hear" a Stars Nuclear reactions if you were close to it? Hey all, This is more of a thought problem, but last night I was wondering about what it would be like to see a star up close (relatively speaking). Since stars are essentially a massive nuclear chain reaction you would think...
  26. P

    Momentum and Newton's Gravitation force question (2 stars)

    At t = 0 a star of mass 5.0×1030 kg has velocity < 6.0×10^4, 7.0×10^4, -7.0×10^4 > m/s and is located at < 1.00×10^12, -4.00×10^12, 4.00×10^12 > m relative to the center of a cluster of stars. There is only one nearby star that exerts a significant force on the first star. The mass of the second...
  27. binbagsss

    Stars, fusion, how exactly the weak interaction acts ?

    I am currently reading E=Mc^2 and have a quick question regarding some of the nuclear fusion they describe that takes place in stars: When proton fusion occurs, one of the protons decays into a neutron + positron + neutrino – due to the weak interaction. And the proton and neutron , acted...
  28. S

    Why don't shooting stars make a noise?

    Pretty self explainable. Why do they not create a sonic boom when they enter Earths atmosphere
  29. D

    Motions of stars inside elliptical galaxies?

    I recently read an article about elliptical galaxies. The article mentioned that the stars have basically radial motions. What does that mean ? Do these stars oscillate between the center and some mid-radius? Stars in spiral galaxies have on average orbital motions in one direction around...
  30. F

    How Do Eclipses Affect the B-V Index of Identical Binary Stars?

    Hello. Given a binary system with two identical components (in particular de B-V index of both is the same), how would you calculate the B-V index of the system? and, how would it change during eclipses? I have my own answer, but want to contrast it against yours.
  31. D

    Velocity of the Sun Through Stars: Time & Distance to Collision

    Homework Statement The sun moves through the collection of stars in it's neighborhood with velocity v=10 km/s. (A)Assuming n*=1 pc^(-3) and that all starts have the same radius R*, what is the typical time we must wait before the sun collides with another star? Express your answer first in...
  32. M

    Planetary Systems within Elliptical Binary Stars?

    I read this article in Nature (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10768.html) as it describes two circumbinary planets. If it is assumed that most stars have a planet orbiting it and most Binary Star systems are elliptical, then wouldn't the majority of Binary Stars...
  33. R

    How Long Do Red Giant Stars Last?

    I have been unable to find any data or formula's on how long red giant type stars last other than a few million years!One would suppose that it is a function of its original mass and chemical composition. Any ideas...
  34. T

    Why Are Giant Stars So Low in Density?

    Why giant stars are so low in density?
  35. N

    What elements make up the core of a dying star?

    Okay, so so you got two forces acting on a star. Gravity trying to compress it, and the internal pressure, caused by fusion, pushing it out. For the star's life they are at equilibrium, but the star dies when it runs out of nuclear fuel. Then why do some stars explode? Shouldn't they all...
  36. 0

    Why is it considered the 'end of the universe' when the stars go dark?

    Why is it considered the 'end of the universe' when the stars go dark?? As I understand it, there were two main theories accepted regarding the expansion of the universe after the big bang. One of them assumed that the expansion would start to contract, the other that it would continue to...
  37. S

    Question about colour of stars and planets.

    The sun appears yellow because is made of white light and blue,green,indigo gets scattered.My question is why the planets and the moon appear white with their case the same thing should happen and even they should appear yellow.
  38. D

    If the universe is truly expanding, why aren't any stars getting dimmer?

    The intensity of light observed from a given source decreases as the square of the distance between the observer and the source. Hence, if stars are truly receding from the earth, the intensity of light observed from any such star should be getting dimmer as time goes by. But the intensity of...
  39. T

    Questions concerning hypervelocity stars

    Hey everybody, I'm new here and what better way to start then jump right in! I have a few questions concerning hypervelocity stars for a sci fi book that I want to write. First of all, what is the agreed upon "average" speed of a hypervelocity star? I have done a bit of googling, but I have...
  40. D

    A night with the stars (Brian Cox on telly)

    http://www.bbc.co.uk/programmes/b018nn7l I did enjoy Brian Cox's program on quantum mechanics last night, but one bit left me thinking "no, that's not right!". The gist of it was that all the electrons in the universe have to be in constant communication to ensure that no two of them are...
  41. S

    Are supermassive black holes just big stars?

    Simple enough question. I know there are two types of black holes; the type formed after a star collapses in a supernova and the supermassive variety like the one at the center of the milky way. If a star continued to grow by swallowing up other stars and solar systems is it possible that at a...
  42. B

    The initial mass function (IMF) of main-sequence stars,

    I need help to solve this problem: The initial mass function (IMF) of main-sequence stars, n(M) follows a shape called the Salpeter function,which is described by n(M)=kM^-2.35, where k is a normalising constant and M is the stellar mass in solar masses. The IMF is similar in some sense to a...
  43. W

    Can a human travel to distant stars? And other questions.

    1. Can a human travel to distant stars? If the faster you go the slower the time passes for you, then you could technically travel to stars several thousands of years distant from you. It could take thousands of years for someone on Earth, but just a few days for you. 2. Why can't we travel...
  44. C

    Binary stars apparent and absolute magnitudes

    Homework Statement A binary star system has two star of equal luminosity. The apparent magnitude of the two stars together is 11.2, and they are at a distance is 76pcs. How do I work out the apparent and absolute magnitudes of just one star? Homework Equations m=-2.5log(L)...
  45. G

    Minimum angular separation for viewing stars

    Homework Statement What is the minimum angular separation an eye could resolve when viewing two stars, considering only diffraction effects? Homework Equations Rayleigh criterion: θ=(1.22*λ)/D The Attempt at a Solution This problem doesn't give very much to go on so I think...
  46. manojr

    Are exploding supernovae responsible for heavy metal content in ancient stars?

    I was reading news article: http://www.sciencedaily.com/releases/2011/11/111115095911.htm Article explains in beginning that when star explodes as supernova, heavier elements are formed which later become part of new generations of stars. And in concluding paragraph, article says "reason why...
  47. P

    Kinetic energy of gases in stars

    Hi, I have a conceptual and mathematical question about gases in stars. The information we have from stars is due to the motion of particles in one dimension: along our line of sight. We assume that this motion is isotropic and that regardless of where on the star we look, we'll get the...
  48. P

    Kinetic energy of gases in stars

    Hi, I have a conceptual and mathematical question about gases in stars. The information we have from stars is due to the motion of particles in one dimension: along our line of sight. We assume that this motion is isotropic and that regardless of where on the star we look, we'll get the...
  49. A

    Can variable stars become quickly non variable and viceversa?

    Can a variable star become a non variable one? Or viceversa, can a non variable, as it is (almost) the sun, become quickly (say few thousands of years) a variable one? Is there any record (e.g. in the geological records) which shows that the sun had once a very different luminosity? Has this...
  50. P

    What is the ultimate fate of a massive star in space?

    Introduction Deep in the vastness of space, beyond our solar system, stars are born in primordial nebulae, gaseous molecular clouds on the spiral arms of galaxies extending across the heavens. Intense gravitational forces compress the cloud causing temperature and pressure to increase...
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