SUMMARY: Astronomers have found three red supergiant stars which are huge; bigger than anything previously discovered. The three stars are called KW Sagitarii (9,800 light-years away), V354 Cephei (9,000 light-years away), and KY Cygni (5,200 light-years away). All three are 1,500 times bigger than our own Sun, and would reach out midway between Jupiter and Saturn if they were in our Solar System. These stars aren't extremely massive, though, they're only 25 times the mass of the Sun (stars have been discovered which have 150 times the mass of the Sun).

View full article

What do you think about this story? Post your comments below.

It is interesting to think about how long these stars might stay this size. They are late in the evolutionary process, and probably will change substantially over the next few centuries [short astronomically, long for a career].

The closest of these should be about 0.6 arc-seconds in diameter, so with out best instruments, we ought to be able to get an image of it dozens of pixels across.

__________________
Forming opinions as we speak

IT IS VERY CONFUSING TO THINK ABOUT HOW THE STARS COULD HAVE SWELLED THAT MUCH. <_< :blink: IT KIND OF POOPS ME WHEN I THINK OF AN OBJECT ( NOT A BLACK HOLE) :wacko: WITH A BILLION MILE EQUATOR. I MEAN, REALLY.

Welcome guest. While we welcome your comments, I would ask that you please refrain from yelling at us.

As to the size of these stars, at 1billion KM, these are about 100 times the size of the sun. Our sun will swell up to about 750,000,000 KM give or take, so they are really not that much bigger,

__________________
All civilizations become either spacefaring or extinct.~ Carl Sagan ~

Humanity must rise above the Earth, to the top of the atmosphere and beyond, for only then will we fully understand the world in which we live.~Socrates, 500 B.C. ~

Let every man judge according to his own standards, by what he has himself read, not by what others tell him. ~Albert Einstein~

Looks like a good place for me to ask why some stars swell at the end of their lives. I can understand the fusion process generating heat but does this not result in something denser? Is it through occretion?
Go on, I'll stop guessing.

It has to do with stellar evolution. A star with about the mass of our sun will burn through its hydrogen fuel over the course of several billion years. As the star depletes its supply of hydrogen in the core, its thermal equilibrium becomes unbalanced and the pressure in the star's core lessens. Thermal equilibrium unbalances because the fusion of four hydrogen atoms into one helium atom decreases the number of particles present in the star's core. The star begins to collapse inward because fewer particles means the star cannot maintain the pressure needed to support the star's outer layers.

Without the necessary pressure, the star's core contracts slightly under the weight of its outer layers. This collapse increases the pressure and temperature of the core, causing the luminosity of the star's surface to increase. This increase in pressure on the layers just outside the core raises their temperature to the necessary point in which the outer layers of hydrogen begin fusion.

This occurrence of hydrogen fusion in the outer layers of a collapsing star is called shell hydrogen burning. Shell hydrogen burning allows the star to remain in the main sequence for another few million years. During this period the higher temperature of the star causes the outer layers of the star to expand--it becomes a red giant.

__________________
All civilizations become either spacefaring or extinct.~ Carl Sagan ~

Humanity must rise above the Earth, to the top of the atmosphere and beyond, for only then will we fully understand the world in which we live.~Socrates, 500 B.C. ~

Let every man judge according to his own standards, by what he has himself read, not by what others tell him. ~Albert Einstein~

I have read several articles about these 3 super giants, many saying nearly the same thing while others offer some unique info.

But none so far have given location data as to where these stars can be found. Particularly, I am interested in RA/DEC info if anyone has that available.

Thx.

I have a series of webpages talking about a supernova, and one of them discusses why stars swell up near the ends of their lives. I hope that helps.

__________________
Phil Plait
The Bad Astronomer
http://www.badastronomy.com
badastro@badastronomy.com