The Largest Known Star

Beagle · Post by **Beagle** » Mon Apr 14, 2008 4:49 am

http://www.techdo.com/images/largest-know-star.htm

This is nice imagery of some of the celestial bodies that are known to us. The Earth comes up first. Just wait for the rest. The program repeats.

CShark · Post by **CShark** » Mon Apr 14, 2008 8:17 am

Beagle wrote:http://www.techdo.com/images/largest-know-star.htm

This is nice imagery of some of the celestial bodies that are known to us. The Earth comes up first. Just wait for the rest. The program repeats.

Thanks for this Beag, great stuff. Never knew Betelguese or Antares were in that class..makes you stop and think about how small and fragile we really are....

War Arrow · Post by **War Arrow** » Tue Apr 15, 2008 7:07 am

Bloody hell!

Digit · Post by **Digit** » Fri Apr 18, 2008 5:04 am

Makes me wonder how large they can be.

War Arrow · Post by **War Arrow** » Fri Apr 18, 2008 6:34 am

Totally off topic, though not quite off subject exactly - thought I may as well ask whilst I'm here. FM - I've recently been reading a lot by a science-fiction author called Stephen Baxter - pretty compelling writing and he seems to be pretty hot on his quantum theory and suchlike, so I was kind of surprised to read a story referring to conditions on the planet Mercury which made no mention of radioactivity. Is my memory of such things failing or has Baxter messed up and mislaid the fact of Mercury's surface being saturated with radiation due to 88 (?) day "days" facing the sun?

Beagle · Post by **Beagle** » Fri Apr 18, 2008 3:23 pm

Digit wrote:Makes me wonder how large they can be.

My thoughts exactly Dig. At some point though, I think the mass would be so great that the star would collapse in on itself, creating a black hole. But I wouldn't know how big that would have to be.

Digit · Post by **Digit** » Fri Apr 18, 2008 3:28 pm

That was how I reasoned it Beag, perhaps Monk will come up with an answer.

Beagle · Post by **Beagle** » Fri Apr 18, 2008 3:35 pm

perhaps Monk will come up with an answer.

Yep. He'll see this sooner or later.

Forum Monk · Post by **Forum Monk** » Fri Apr 18, 2008 4:12 pm

The size of the star is often determined by its age. VY Canis Majoris is about 2100 solar radii but some astronomers think that is generous and would say it closer to 600 solar radii. Enormous in any case since a solar radius is about 432,000 miles. It is believed a star could grow as large as 4600 solar radii (perhaps a little more). This is pushing 2,000,000,000 (two billion) miles.

The mass of a star often determines its stability and whether or not it will collapse upon itself. The stability limit is somewhere around 150 times the mass of sun for conventional stars. Stars must balance their explosive radiation with gravitational attraction. Too much of one or the other and you have a star which either sheds its shell or collapses. The physics is a bit more complicated than my over-simplification but I think you should understand the basis of what I am talking about.

Hard to tell if the theoretical limits in size and mass have been achieved somewhere in the universe as much of it is obscured from our view.

btw - saw the slide show about a month or so ago on another board.

Digit · Post by **Digit** » Fri Apr 18, 2008 4:18 pm

Those images Monk show stars at various stages of their life cycle, but even allowing for the swelling that can take place at certain stages, there's some big 'uns there.
I wonder if a star can become a black hole before it runs out of fuel?

rich · Post by **rich** » Fri Apr 18, 2008 4:23 pm

Here's a simplification of it:
http://www.rdrop.com/users/green/school/form.htm

And here:
http://imagine.gsfc.nasa.gov/docs/ask_a ... 0210b.html

Forum Monk · Post by **Forum Monk** » Fri Apr 18, 2008 4:39 pm

The complete life-cycle of a star is explained beautifully in this link: listen to it, read it or read as you listen.

Fraiser Cain is editor of Universe Today (UT) and Dr. Pamela Gay from the University of Southern Illinois.

http://www.astronomycast.com/astronomy/ ... -they-die/

Digit · Post by **Digit** » Fri Apr 18, 2008 4:40 pm

But in each case Rich they talk about a star running out of fuel first. How about this? A dense cloud of matter begins to fall inwards under gravity, its mass grows till it finally 'lights up', then according to theory it can't grow larger 'cos the pressure of the star's light pushes the remaining gas cloud away, if that is correct, logic says all stars should be about the same size!
If that is not correct what stops a star from growing till its gravity causes it to collapse, does increasing gravity raise the temp high enough that the individual particles are too far apart to permit gravitational collapse. Wake up Monk, you're needed!

Forum Monk · Post by **Forum Monk** » Fri Apr 18, 2008 4:41 pm

Our posts crossed Digit. Look back one post.

Digit · Post by **Digit** » Sat Apr 19, 2008 7:25 am

Doesn't answer my question Monk. As stated the star clears the area around it as soon as it lights up, thus preventing any further growth. If all stars light up at the same internal temp, which must be determined by the heat needed for the fusion cycly to start, then all stars should be about the same mass at the time they light up.
Now a star's colour in effect tells us how far through its life span it has progressed, you can't have a dull red star, for example, that is into the earlier part of the hydrogen cycle, also as the star ages its size will change but my point was that some of the stars shown in the images seemed very large but were young, based on their colour. How can that be if the theory is correct?
If all stars light up at the same mass then all G6 stars, like ours, should have the same mass as ours and be the same age as ours.
Help!

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The Largest Known Star

The Largest Known Star

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