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mopc
2004-Jul-28, 04:39 AM
Can anybody tell me what are the largest and smallest stars known (in terms of mass and diameter)? Could you include the size of the most famous stars, like Alpha and Beta Centauri, Betelgeuse, Sirius, etc. Not to mention quasars, pulsars, etc.

If there are any links to this kinda info, please!

Manchurian Taikonaut
2004-Jul-28, 05:19 AM
super sized star, at one time it was thought to be Alpha Herculis but astronomers now think Epsilon Aurigae is 2,700 times the Sun's size, far larger than alpha the red giant Betelgeuse or Alpha Herculis

mopc
2004-Jul-28, 05:43 AM
2,500 times the mass or diameter of the Sun???

Kullat Nunu
2004-Jul-28, 06:28 AM
2,500 times the mass or diameter of the Sun???

Diameter, although it is no longer believed to be so large. Epsilon Aurigae B (the star) has most likely a dust disk surrounding it. See more about it from Jim Kaler's Stars (http://www.astro.uiuc.edu/projects/sow/almaaz.html) site. I don't now which star is believed to be the largest in diameter, but the Garnet Star (Mu Cephei) is one of the largest known. Its diameter is larger than the diameter of Jupiter's orbit.

In fact, stars cannot weight much more than 100 solar masses (that border is very ambiguous), otherwise nuclear reactions inside the star become so intense that the star rips itself apart. Actually this happens in the most massive stars like Eta Carinae or Pistol Star. They lose much of their mass before exploding as a supernova.

In very early Universe, when there was only hydrogen and helium, stars weighting over thousand Suns were possible, since there were no heavier elements to act as catalyst in nuclear reactions. We are not sure if such stars really existed, though.

Kullat Nunu
2004-Jul-28, 06:52 AM
Here (http://www.tim-thompson.com/bright-stars.html) is a list of the brightest (and most massive) stars in the Milky Way.

The most massive star known is LBV 1806-20, which probably has a luminosity 40 million times larger than the Sun.

It is much harder to determine which star is the smallest one in mass. Objects weighting between 12 and 80 Jupiters are considered brown dwarfs. Objects heavier than 80 Jupiters are stars, since they are capable to sustain hydrogen fusion. Brown dwarfs can fuse deuterium (heavy hydrogen) into helium for a short time.

In the main sequence, the dimmest red dwarfs are the smallest in diameter, they are about as large as Jupiter.

White dwarfs are much smaller, about the size of the Earth. Because of gravitational compression, more massive a white dwarf is the smaller its diameter is. Smallest white dwarfs weight 1.4 Suns, since it is the upper limit for white dwarfs (if a white dwarf crosses this line it blows up as a type Ia supernova).

If we count neutron stars as stars, they are of course much smaller still, only a couple of tens of kilometers. They too are gravitationally compressed. The upper limit for a neutron star is poorly known, but it is something 2-3 solar masses.

Masses and diameters for neighboring and famous stars can be found at Internet Stellar Database (http://www.stellar-database.com/).

And mopc, quasars are not stars, but very active regions in the centers of distant galaxies. They do look like stars, though. The central engine, supermassive black hole, is about the size of the Solar System.

Brady Yoon
2004-Jul-29, 05:33 AM
Could you include the size of the most famous stars, like Alpha and Beta Centauri, Betelgeuse, Sirius, etc. Not to mention quasars, pulsars, etc.

http://www.cosmobrain.com/cosmobrain/res/brightstar.html

Here's a list of the 50 brightest stars in the night sky (in terms of visual magnitude). However, the properties of more distant stars are generally not well known because the methods in which they are determined are a little inaccurate.