Most luminous star?

[kelle]

I was playing around in Celestia recently and found a star (HD 7389 / HIP 5926) which Celestia claims has a luminousity 79,600 times that of our sun ( snapshot from celestia enclosed <img src="/images/icons/smile.gif" /> )! Is this star really this powerful, and does anyone know what is the most luminous star we know about? Also I wonder how long such a powerful star like this could live for? That can't be long.

 

[jcdenton]

<i>Astronomers using the Hubble telescope have identified what may be the most luminous star known ? a celestial mammoth that releases up to 10 million times the power of the Sun and is big enough to fill the diameter of Earth's orbit. The star [center of image] unleashes as much energy in six seconds as our Sun does in one year. <br /><br />The image, taken in infrared light, also reveals a bright nebula [magenta-colored material], created by extremely massive stellar eruptions. The nebula is so big (4 light-years) that it would nearly span the distance from the Sun to Alpha Centauri, the nearest star to Earth's solar system.</i><br /> <div class="Discussion_UserSignature"> </div>

 

[jcdenton]

BTW, that's a pic of the Pistol Star, taken from HubbleSite. <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

I am confused.Is kelle right or wrong?

 

[qzzq]

LBV 1806-20. <br /><br /><ul type="square">Space.com: Biggest, Brightest Star Puzzles Astronomers ATLANTA – A team of researchers has found what appears to be the most luminous known star around, one so massive that it shouldn’t have formed in the first place.<br /><br />The star, known as LBV 1806-20, tips the scales of stellar masses at about 150 times the heft of the Sun. It shines up to 40 million times brighter than the Sun. The previous title-holder called the Pistol Star, is a mere six million times brighter than the Sun and weighs about 100 solar masses.</ul> <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>

 

[jcdenton]

They don't know the exact luminosity of LBV 1806-20 yet, it can be anywhere from 5-40 million Suns. Here's a size comparison with the Sun... <div class="Discussion_UserSignature"> </div>

 

[kelle]

Whew... 40 million times the luminousity of the sun... that's... awesome! And the size of that LBV 1806-20... whew!! There can't be much that's more fascinating than the enourmous sizes and monstrous amounts of energy involved in giant stars. But I couldn't find any of those "millions of times more powerful than our sun"-stars in Celestia? They're not there?!? And are the pistol star and LBV 1806-20 and the other giant stars, stars in the ends of their lives, so they have swelled up, or are that their normal size? How long does such extremely huge stars live?? A few million years?

 

[jcdenton]

Yes, blue giants like the Pistol Star or LBV 1806-20 only have a short life of tens of millions of years due to their extreme temperature and mass. Eventually they'll burn out and cause supernovae. <div class="Discussion_UserSignature"> </div>

 

[rybanis]

The Pistol Star is interesting, as it lies only a few hundred light years (IIRC) away from the leading edges of the plasma flows that lead into Sag A*. Sky and Telescope had an awesome article about the Galactic Core a few months back. <div class="Discussion_UserSignature"> </div>

 

[Maddad]

The Pistol and LBV 1806-20 are the brightest stars today because they are the most massive, around 150 or 200 solar masses. Their lifespan is directly proportional to their mass and inversely proportional to their energy output. We expect them to live only about one 200,000th as long as our own sun's main sequence life of 10,000,000,000 years. These heavyweights will therefore shine perhaps as little as 50,000 years.<br /><br />Amazingly enough they are not the most massive stars there ever were. In the first few years after the big bang all stars were composed of hydrogen, helium, and lithium only. They had no heavy metals because these would be created by the deaths of these early stars. Also, the gas clouds that these first stars formed in were extremely more massive than the gas clouds within galaxies that exist today. Finally, these gas clouds were much warmer than their present-day counterparts.<br /><br />These three factors together mean that some of these very first Population III Stars were as much as 100,000 times as massive as our sun. It is hard to calculate their luminiosity because you have to extrapolate three orders of magnitude beyond the available data. If there is a knee in the log line, meaning that the line curves and we don't know it, then our estimate will be wrong.<br /><br />That being said, when a star 100 times more massive than our sun, then it is a million times brighter. This is a rough cubic relationship. Extend that three more zeros for a star 100,000 times as massive as our sun and you get a star that is a quadrillion times brighter (1,000,000,000,000,000 or 10¹⁵ L). Since it has 100,000 times as much mass to start with, it will burn through it's main sequence lifespan in a ten billionth the time our sun does, just about one year.<br /><br />It won't last long, but it makes one hell of a night light while it's lit.

 

[qzzq]

Good to see you again, maddad. <img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>

 

[newtonian]

maddad - Now, how would one define a star? Would a supernova be a star? Or a hypernova? And how do these compare in the luminosity record books?<br /><br />Ditto a quasar?<br /><br />Good point about the oldest stars. Are the oldest stars we observe, near our visibility horizon, also brighter?<br /><br />Or was universal density too great back then to allow these early bright stars to let their light shine on us.<br /><br />And, yes, welcome back!

 

[Maddad]

Thanks for the welcome back guys. It was so hard getting in here after the July 2nd crash that I though perhaps I'd been banned. Again.<br /><br />A star starts as a gaseous object at least 0.08 times as massive as our sun, about 75% hydrogen, 24% helium, and as much as 1 or 2% heavier elements.<br /><br />The supernova is a an end stage in a more massive star's life. After fusing into iron all lighter elements in the core, the fusion process shuts off like a light switch. In miliseconds the core collapses. About 10⁵⁸ electrons and protons combine to create neutrons, each one releasing a neutrino. The rebound from the core, assisted by the outrushing neutrinos, blasts much of the star's matter into space. Depending on the initial mass of the star, enough of the core might remain to produce either a black hole, a neutron star, or even nothing at all. The excess energy is the only natural process that creates elements heavier than iron. Since some of these newly created elements are radioactive, their radiation contributes significantly to the luminiosity of the supernova during the next two months while it fades from sight.

 

[thalion]

I'll bite.<br /><br />Let's take the most conservative estimate for LBV 1806-20, at 5 million solar luminosities. The equivalent terrestrial distance is quite easy to calculate, using the inverse square law. The Earth--or some other planet--would have to orbit at a distance where the square root of the luminosity would equal the equivalent distance. For instance, for a star 50 times brighter than the Sun, the Earth would have to orbit (50)^.5 x 1 AUs farther away, or about 7.07 AUs. For a star of 5 million luminosities, the equivalent terrestrial distance is the square root of that number in AUs, or 2236 AUs, which is about 1/30th of a light year. For a star of 120 solar masses, the orbital period of this new Earth would still be huge, at some 9650 years. <br /><br />

 

[rybanis]

Wow, now thats amazing. <div class="Discussion_UserSignature"> </div>

 

[Saiph]

looks good to me, nice calculations. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>