Starship Asterisk*

Looking for the quasar in the Time Tunnel photo, I found the two vertical bars, but is the quasar the bright spot above the top bar, or is it the dim smudge in between the bars? Thanks for clarifying.

Generally with that sort of marker, the item of interest is between the two short lines.

It is the very faint star between the vertical markers

Hello welshj, and welcome to the APOD forum,
It helps to put the URL to the photo you are wanting to discuss, or question, in your thread title, or in your post, so others can relate and know which APOD you are talking about.

http://antwrp.gsfc.nasa.gov/apod/ap070906.html

Qev and BMAONE23 seem to have answered your question so I will only add that it is pretty cool to be able to use such areas of the sky to see farther than one could normally.

Norval

Hello.

The comment states that the quasar is 12.7 billion light years away. I believe that this statement is untrue.

This quasar is 12.7 billion years old. So the light crossed 12.7 billion light years. In my opinion, this doesn't mean that the quasar is 12.7 billion light years away. I believe that, because of the Universe expansion, it was far closer when the light was emitted and that it is much further today.

Please, correct me if I'm wrong.

Patrick

Hi Pyjam. Welcome.

Assume a beam of light travelled in a straight line in a vacuum for 12.7 billion years from the quasars position in space (way back then) to our position in space (right now). With those assumptions, one can say that the those two points in spacetime were separated by 12.7 billion light years.

We think the quasar was moving away from us (back then) at a speed of roughly 1/1000 the speed of light, enough to give it a big red shift. If it moved directly away from us at that speed for 12.7 billion years, it would be 12.7 million light years further away now. I have no idea in what direction or how quickly it has moved since 12.7 billion years ago. Presumably, it no longer exists as a quasar anymore, and hasn't for billions of years.

Our position in space has been moving, too. The solar system formed some 4.5 billion years ago and has been moving ever since. But I don't think where we have been over the past 4.5 billion years has much bearing on that light beam that travelled though spacetime from where it was to where we are.

That being said, one can begin tearing down the original assumptions. Did the light beam travel through a vacuum the whole way? I doubt it. Did gravity from other objects distort the path of the beam during it's 12.7 billion year travels? Probably. Is geometric space over such a vast distance really a straight line? ???

Hello !

I don't speak about the quasar's own movement. I neglect it. I speak about the effect of the Universe's expansion. Please, have a look at the observable Universe article in Wikipedia :

For example, the cosmic microwave background radiation that we see right now was emitted about 13.7 billion years ago by matter that has, in the intervening time, condensed into galaxies. Those galaxies are now about 46 billion light-years from us, but at the time the light was emitted, that matter was only about 40 million light-years away from the matter that would eventually become the Earth. See comoving coordinates.

http://en.wikipedia.org/wiki/Observable_universe

If I understand well, the quasar in the APOD article stood at a distance of 40 million ly from Earth when the light was emitted 13.7 billion years ago. It is now at a distance of 46 billion ly. In our case, the distances are different because it's 12.7 B years, not 13.7 B years.

It is also possible that I don't understand the Wikipedia article.

Pyjam

I read the Wikipedia article (it's worth a look and a good solid critique; I don't believe every Wiki I see) which states the age of the universe at 13.7 billion years, and the radius of our sphere of the universe at 46.5 billion light years. I'll accept those figures for the sake of discussion. I think you are confusing the background radiation emitted 13.7 billion years ago with the quasar signal emitted 12.7 billion years ago. Keep them separate in your mind.

Most of the expansion (inflation) of space in the universe occured rapidly 13.7 billion years ago, and the universe has been expanding relatively slowly since then. So perhaps the original source of the background radiation is 46.5 billion light years away now, but the quasar, which emitted it's radiation 1 billion years later, has not had time to get out to the edge of our sphere. Even if space expanded at a pace equivalent to 50% of the speed of light that whole time, it could only be 19 billion light years away from us now. Plus it doesn't exist now anyway; it's burnt out and has been recylced into a different dust cloud or galaxy by now.

Other opinions?

welshj wrote:Looking for the quasar in the Time Tunnel photo, I found the two vertical bars, but is the quasar the bright spot above the top bar, or is it the dim smudge in between the bars? Thanks for clarifying.

Why don't u put the URL to the photo? Without the photo I don't know which APOD you are talking about.

Hello 0adomi,

First of all, welcome to the forum. I'm no one of any consequence, fust happened to see your posts and thought I could be of some help. The date for this picture appears in the subject line at the top of the first post in this particular thread.

astrolabe wrote:Hello 0adomi,

First of all, welcome to the forum. I'm no one of any consequence, fust happened to see your posts and thought I could be of some help. The date for this picture appears in the subject line at the top of the first post in this particular thread.

Thanks, guy. I'm a freshman of the forum. I happened to see the Astronomy Picture, and it's really a special attraction. Now I have an obsession with it.