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.

View More On Wikipedia.org
Recent contents Top users
  1. P

    Counting Stars in Universe: How Big Bang Began

    So my first question is, how do we know how many stars are in our galaxy? And the second is, how do we know the big bang started with a singularity (as opposed to, say, the universe being a few light years wide and then start expanding 13.7 billion years ago until it reached our present size)...
  2. P

    Are there any stars that do not have a planetary system?

    At first, scientists found stars with planets and think that there are suns with planetary system. But it seems now that every sun has planets. My questiion is are there any suns without a planet.
  3. Q

    Binary Stars and Their Planets

    I have a question regarding binary or multiple star systems and their [hypothetical] orbiting planets. I am curious if it is common (or even possible) for one or more of the orbiting planets to constantly switch the star they are orbiting, as in a figure eight shape. Can the stars "trade the...
  4. S

    Will Black Dwarfs Become Iron Stars in 10^1500 Years?

    If the proton does not decay, will black dwarfs become iron stars in 10^1500 years>
  5. S

    Stars and planets made out of antimatter?

    Can there be stars and planets made out of antimatter?
  6. M

    Determining the individual magnitudes of two stars

    Firstly please if you reply don't post the solution, rather the method you would use to get it as I'm trying to learn how to answer this kind of question for an exam. the problem (quoting my question paper): the stars S1 and S2 are seen along the same line of sight from Earth. Srat S1 is...
  7. H

    Neutron Stars and Special Relativity

    Neutron Stars and Special Relativity and General Relativity Here is a question which I can't quite wrap my head around: Suppose we have a Neutron Star that is borderline on the Chandrasekhar limit in its rest frame. In another frame, the Neutron star is moving. As a result, its density...
  8. S

    Distance to stars from my house using the parallax technique?

    Is it possible to find the distance to stars from my house using the parallax technique? If I can how close does a star have to be to be measured in a month instead of six months?
  9. H

    Distance to Stars: Calculating the Distance from Sun

    Homework Statement Two white dwarfs are found to lie within 16 arcseconds of each other on the sky. The probability that such an alignment occurs by chance is very small. Therefore, they are almost certainly physically associated, lying at the same distance fr0m the Sun. One of the stars...
  10. M

    What happens to a 0.7 solar mass star when it comes off the main sequence?

    Let's say we have a star of 0.7 solar masses on the main sequence. Can somebody describe what happens to it when it comes off the main sequence? Thanks Maria
  11. T

    Beginner's question on bending of space time and measuring distance to stars

    Hi Everyone, First post here. I'm a 37 year old man who has just recently begun dabbling in the basics of Physics, purely for the academic enjoyment of making by brain go "ow!". Upon reading the "bowling ball on a bed sheet" description of how the gravity of large objects can bend the...
  12. F

    Naming Stars: A Scam or Legitimate Organization?

    What organization is the official namer of stars? The reason I ask is with all the new Earth sized planets being found and the eventual identification of those with at least water and perhaps signatures of life by spectral analysis, the planet first found as such, I believe at least, should...
  13. R

    Finding Period with Double Stars

    Homework Statement A certain double star consists of two identical stars, each of mass 3.0E30 kg, separated by a distance of 2.0E11 m between their centres. How long does it take to complete one cycle? Give your answer in seconds. Homework Equations Gm / 4π^2 = r^3/ T^2 (I'm...
  14. C

    Age of the sun+age of previous stars = universe ?

    I'm always perplexed by the numbers I see on estimates of the age of the universe and the age of our solar system. Somehow, I don't see it adding up. Here's my logic, plese point out the flaw: 1- Current estimate of the age of the universe : 13.73 billion years give or take. (when I was in...
  15. W

    Star Catalogue Question - Stars near the Ecliptic

    I'd like to create a catalogue of stars that are within a one degree belt along the ecliptic. Since most databases use RA/Dec coordinates, this appears to be a daunting task. Any suggestions?
  16. P

    Do the positions of stars determine our position in time,or does our

    Do the positions of stars determine our position in time, or does our position in time determine the positions of stars?
  17. C

    Calculate distance between stars in a globular cluster?

    Would it be possible to calculate the approximate distance between stars in a globular cluster by doing something simple like this: Approximate distance to a cluster: 25,000 Ly Two stars in the cluster just barely resolved in my telescope (resolution about 1 arcsec) Therefore: 2pi...
  18. C

    Relativity- stars and spacecraft.

    1.a.) A star is 450 light years from earth. i) what is the minimum time a spacecraft could make a return trip to this star? ii)How fast should the spacecraft travel to make the journey in 30 astranaught years? iii) What is the distance of eart to this star as measured by the astronauts on...
  19. F

    Masses of Binary Stars: Calculate from Motion

    mass of stars? Homework Statement About half of the visible "stars" are actually binary star systems, two stars that orbit each other with no other objects nearby. Consider the motion of the center of mass of a binary star system. For a particular binary star system, telescopic observations...
  20. F

    Neutron stars and magnetic fields

    Since neutrons have no electric charge, how is it that a neutron star is able to produce a magnetic field? :confused:
  21. Z

    Measuring Star Diameter in Foreign Galaxies

    Is it possible with our current technology to measure the diameter of stars in galaxies other than our own?
  22. V

    Calculate the Masses of two binary stars

    Homework Statement I am trying to understand the following example question in my course book, The answer is actually given but i don't understand how they got to it, i would like someone to give me an idea how this has been worked out In the Sirius Binary system the orbital period is 50...
  23. M

    Exploring Star Spectra: A Beginner's Guide

    I'm doing a project about astronomy. I've never done one, I just jumped from quantum physics to here, so I don't think I know anything =.=. To start, I think I need some stars spectrum, but since stars are not as bright as the sun, I don't really know how to have them. Could someone give me some...
  24. marcus

    Studying the formation of the very first stars

    Understanding the first star formation is critical to cosmology. Matt Turk is a (remarkably young) expert on this. The way they go about it is with computer simulations and checking the results against whatever can be observed. Here is a talk by Matt Turk...
  25. K

    Newton's 3rd Law applied to binary stars

    Below is a question I recently got wrong, and the (automated) feedback. Since the stars are in a stable configuration, I realize that the forces must be equal, but I thought that the differing gravitational forces were balanced by the centripetal forces of the orbit (the smaller star being...
  26. R

    Binary Stars: Equal Mass, 350 Million km Separation, 5.4 Earth Years Orbit".

    Suppose that a binary-star system consists of two stars of equal mass. They are observed to be separated by 350 million {\rm km} and take 5.4 Earth years to orbit about a point midway between them. I got 1.1x10^29 as my answer, but it is incorrect. Can anyone help me out?
  27. M

    How Do Two Stars Orbit Each Other with Equal Masses?

    Their are 2 stars orbiting one another. Their masses are equal. The speed at which they rotate is 220 km/h, and their orbital period is 14.4 days. Find the mass of the Star. Homework Equations 220km/h = 61.1m/s 14.4 days = 51840s V= 2pi(r)/T F=ma F=mv^2/R F= m4pi^2r/T^2 Fg=...
  28. D

    Are There Stars Made of Something Other Than Hydrogen?

    Why are stars different sizes? Are there stars made up of something other than hydrogen? It was my understanding stars are made of hydrogen but if all of them where made of this then they should all start fusion whey they reach critical mass/density making them all relativley the same sizel...
  29. T

    Star Distribution - Types, Galaxies & Time

    I'm quite interested in finding out the % distribution of stars (by type, viz. O,B,..,M), a) within our galaxy and b) within other galaxy types (ex. globular, etc) - and how these distributions change with time. Can anyone sate my curiosity (or point me in the right direction) ?
  30. Z

    How far apart are two stars resolved by a 68-cm telescope?

    Homework Statement Two stars 18 light-years away are barely resolved by a 68 -cm (mirror diameter) telescope. How far apart are the stars? Assume \lambda = 540 <units>nm</units> and that the resolution is limited by diffraction. Express your answer using two significant figures...
  31. E

    How Far Are Stars? Calculating Distance to Earth

    How do people calculate the distnce between Earth and a star?
  32. G

    Collision of 2 Stars: Calculating Angular Velocity & Momentum

    So the question is basically, A stationary spherical star sits at the origin, and has mass 8M and radius 2R. Another sphere of mass M and radius R has a velocity and is coming toward the larger mass. We are to neglect gravitational effect until the 2 masses come into contact. What happens is...
  33. H

    What I see in sky - Milky Way, other stars

    I've wondered about this for a while: -the Milky Way which we are part of appears to be a white cloudish streak in the sky. I guess this is because the stars are so far away that it appears as a cloud of light? -But I would assume that all the stars in the Milky Way, our own galazy, must...
  34. N

    How many stars in the Solar neighbourhood

    Hi all, I was wanting to know of any resources out there that can tell me the how many stars of each spectral type there are in the solar neighbourhood. Any suggestions would be rad!
  35. G

    Astrophysics - Apparent Magnitude of stars in a close binary system

    Homework Statement 2 solar type stars are in a close binary system. Each indivual star has an apparent brightness of m = 10 mag. Determine the apparent magnitudes of the combined system of the 2 stars assuming they cannot be resolved as individual objects. Determine the minimum brightness...
  36. F

    Can We Measure the Diameter of Stars Using Angular Resolution and Other Methods?

    You can get the idea of the size of an object by knowing the distance to the object and the angular distance between the object's edges. Obviously, this is an intuative part of human vision. We can use this method to measure the diameter of our own star. We have methods to measure the...
  37. P

    Stars and electromagnetic waves/radiation

    Homework Statement I am just interested to learn how stars are able to produce electromagnetic waves/radiation (The PROCESS(es)). I am into radio electronics , but have wondered how electromagnetic waves can be produced by stars. I guess 'why' is radiation given off, how is the energy...
  38. S

    Rotating transparent object with stars - what was it?

    I witnessed a rather incredible aerial phenomenon years ago with naked eyes. It was around 2:00AM and a very clear night. As I was talking with someone, I caught something out of the corner of my eye above while I was talking with someone. It was cylindrical-shaped (although the ends seemed...
  39. C

    Hydrostatic equilibrium for stars question

    Hi, I have attatched the question. I have done part a using: m(r) = integral(4pir^2rhodr). Does anyone have any suggestions for parts a and b? Thanks p.s. if anyone knows of a freeware program for paints for macs i would appretiate it rather than having to create pdf's lol
  40. B

    How does the 'atmosphere' of the sun affect ligth from stars passing behind it.

    When the sun goes down over the horizon, we can still see the sun because the light of the sun is bent by our atmosphere. I would imagine that if one were outside of our atmosphere on the far side of Earth away from the sun, yet in a path in line with that light they would also see the sun...
  41. samsara15

    Why do stars and galaxies spin?

    It takes a continuous input of energy to spin, otherwise things would fly apart or stop spinning. So why do large macro objects spin, and continue to spin?
  42. V

    Detecting a stars microwave radiation intensity

    Homework Statement A microwave detector is located 0.5m above the surface of a large lake far from the shore. As a star, emitting monochromatic microwave radiation of 21cm wavelength, rises slowly above the horizon, the detector indicates successive maxima and minima in the signal intensity...
  43. W

    Stars, Ozone, & Evolution of Complex Life

    Earth first formed about 4.6 billion years ago, condensing out of the gases & dust in the proto-Sun's Planetary Disk. But, for about the 1st billion years, the proto-planet was repeatedly pummeled by swarms of Impactors. They deposited gargantuan quantities of energy onto the Earth's surface...
  44. W

    What Life would see around other Stars

    Bigger stars are significantly brighter. That pushes back their Habitable Zones (HZs), where D2 ~ L, which makes them look smaller in the skies of (hypothetical) habitable planets, whose years are also a lot longer: Type Mass Temperature Radius Luminosity HZ-Distance Apparent-Size HZ-Year...
  45. W

    What is Nilssen's Law of Stars and how does it relate to star data?

    By inspection of the following star data (Solar units), we find that: M ~ R3/2 (Nilssen's Law) From this we can derive further scaling laws, for average density (p) and surface gravity (g): p ~ R-3/2 g ~ R-1/2 p ~ g3 Surface gravity (g) acts as a "compressive force" on the star's gases...
  46. S

    Age and metallicity of Population I stars?

    I did some research in regards to the age and metallicity of population I stars in hopes to come up with a novel solution to the Fermi Paradox. Anyways, while the metallicity of the oldest Population I stars can be tracked down to be something like -1 (10% of that of the sun) determining the age...
  47. Philosophaie

    Stars in the Western sky in early evening

    There were two stars one above the other in the Western Sky just after sunset. I think they were planets. One could by Uranus but I am not sure what the other may be. I am at: lat=40.91666667 long=81.43333333 Can anyone help?
  48. S

    Exploring the Possibility of Dark Matter Planets & Stars

    Since Dark Matter is by definition immune to electromagnetic forces, then it has no other way to interact except through gravity -- unless one wants to come up with some entirely new force, which has never been seen. If Dark Matter did have some force of its own, akin to electromagnetism...
  49. Z

    How to calculate the position of stars

    Hi all, hope everyone is doing well this rainy cold night. Hopefully it's not like that wherever you are. Anyhow - I hope someone can help me out. I'm writing some software for a mobile device to create star maps. I've gotten pretty far into it. I'm using data from the Yale bright star...
  50. N

    Gravitational Forces between three stars

    Homework Statement Three stars, each with the mass and radius of our sun, form an equilateral triangle 5.0*10^9m on a side. If all three are simultaneously released from rest, what are their speeds as they crash together in the center? Homework Equations Fg= GMm/r^2 The Attempt at a...
Back
Top