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View Full Version : Massive Stars Slowed Early Galaxy Growth



Fraser
2006-May-19, 11:21 PM
SUMMARY: Shortly after the Big Bang, large clouds of hydrogen collapsed easily into the first galaxies and stars. These weren't stars like our Sun; however, they were hot, massive and very short lived - blasting their environment with ultraviolet radiation. But after the first 100 million years of the Universe, it became very difficult for these dwarf galaxies to grow any larger as this radiation sabotaged further growth. Only the gravity of the largest galaxies could overcome this heat and pressure to grow into larger galaxies over time.

View full article (http://www.universetoday.com/am/publish/big_galaxies_eat.html)
What do you think about this story? post your comments below.

GBendt
2006-May-20, 02:19 PM
I wonder how you determine the size of a galaxy by measuring the absorption which it causes when the radiation from a quasar is passing through it. You only have one 'line of sight', the line from the quasar through one or more galaxies to the telescope on earth. Thus we only get one pixel of the entire picture. This is more than nothing, but we do not know the size of the picture, and we do not know its contents.
The more massive the star, the more shortlived it is, and the higher is its energy output. If I recall it right, the energy output of a star rises by the third power of its mass. Thus, a very massive star may live for less than a million years, and will end violently. After its violent end, there is plenty of time for the dispersing matter of the star to cool down. The Irish have a saying: "As god created time, he created enough of it".
Gravity is a force that cannot be shielded off. It causes galaxies to form, even if there a times when massive stars are disturbing that process.
I read that the universe was created 14 billion years ago. Well, I read that there are galaxies moving away from us at redshifts which assume galaxy speeds close to the speed of light. Some galaxies are so far away that their light is still beyond our event horizon. Well, I read that there are White Dwarfs which are assumed to be 20 billion years old. I think we should be cautious when we speak of the precise age of the universe.

Regards,

Günther

altizar
2006-May-22, 03:42 PM
What got me about this article was the fact that they assumed a universe of normal matter. Not once did I hear any kind of mention of Dark Matter. And seeing as how the majority mass of the universe 80% or so is suppose to be dark matter, I would think that this would play an important fact in galaxy formation. Of course dark matter isn't ionized by ultra-violet radation, so my question is this theory really relevant to anything without the inclusion of dark matter?

Cohen the Barbarian
2006-May-22, 08:25 PM
Günther wrote:

"I read that the universe was created 14 billion years ago. Well, I read that there are galaxies moving away from us at redshifts which assume galaxy speeds close to the speed of light. Some galaxies are so far away that their light is still beyond our event horizon. Well, I read that there are White Dwarfs which are assumed to be 20 billion years old. I think we should be cautious when we speak of the precise age of the universe."

We also hear about pulsars and other objects so far away that we must be seeing them as they were soon after the "Big Bang" (assuming that theory is true). Nobody seems to have mentioned that everything is much more crowded t that distance/time.
Do we have any idea of the size of the universe way back then?

Roy

PhantomWolf
2006-May-31, 08:47 PM
Do we have any idea of the size of the universe way back then?

We still don't, we can only determine how big the universe that we can see is.

This is my take on things. Assume a big sphere, then make it an infinite size. That is the universe. We can see a sphere inside that, centred on us with a radius of perhaps 13 billion light years, but the outside sphere contains an infinte number of those spheres we can't even see since they don't currently overlap.

The Big Bang/Creation was not a single point explosion that then threw stars and galaxies out into the universe from that point, but rather a Big Whomp, where all of space was filled with matter that then started to resolve itself, here, 14 billion light years away and 104 billion light years away. The question is, can parts of the universe we can't, and will never be able to see, be considered a separate universe from ours? To me, no, as someone whose centre of their universe was only 7 billion light years from us would see both our sphere and the next sphere which would prove them to be contiguous.

So really the answer to your question on how big the universe was back then is the same as it is today. It's just the the contents themselves were closer together as space has stretched since then. (Yeah let's try not to have our brains explode by trying to figure out how an infinitely large space can stretch. ;))

Anyways, that's my understanding.