Are the stars really there?

[MorningMajor]

OK, so a slightly melodramatic title, but what I'm getting at is, if a star is 200 million light years away and goes supa nova, will we see it's affects now or in 200 million years time?

I've heard that we might be looking at light from a star that is no longer there any more - is this right?

This all came from a chance remark on another thread whilst talking about Betelegeuse. It's supposedly the next star that we know of to go super nova but is approx 600 million light years away, so. if it "blows" tomorrow will we know instantly? - or will we be seeing it's "still alive" light for another 600 million years? - if so, how do we know it's still actually there?

[Diddydo75]

If a star goes supernova right now and its 200 million light years away, we will have to wait 200 million years for the show.

I think betelegeuse or however it is spelled/spelt is closer to 600 light years away so if it goes bang today we will know in 600 hundred years, well we won't but our kids,kids,kids,kids will ish.

So when you look at objects in the night sky you are actually looking back in time! can't get my head around it sometimes especially the further back you go.

[jwr]

Yes, that's the gist of it. This is one of the tools astronomers are using to investigate the beginnings of the universe. The light from the furthest galaxies is so old it reveals information about a very young cosmos. So by observing them we can effectively look backwards in time - cool eh?

Oh, and I think Betelgeuse is only a few hundred light years away.

James.

[rowan46]

but if we notice tomorrow that it goes up the actual event happened 600 years ago so it could go up tomorrow that is 600 years ago

[jamespels]

There's a very good chance that Betelgeuse has already gone supernova. If it went bang 599 years ago, we'll see out in the next few months (I think diddiyo is about right at 600ly). Of course, in stellar terms, 600 years is nothing so it may have already gone bang, be going bang right now, or not go bang for a few more thousand years...

[Diddydo75]

I hope it does go nova in my life time or get to see it go nova, that would be some sight.

[MorningMajor]

Big oops, sorry I've inserted a few "millions" where I shouldn't have - I meant Betegeuse was about 600 light years away not 600 million!! - DOH! - but the theory's the same!

[ZEbbEDY]

so when looking at m13.. thats actually as it was 25 thousand years ago, thats wild

[david o]

... how do we know it's still actually there?

Quite simply, we don't.

According to current theories nothing, but nothing, can travel faster than light. So the soonest that any info of it's death throes can reach us is the very same moment as the light from the event.

[MorningMajor]

So Hubble sees what we see, though can see more (objects)

[russ.will]

Correct and therefore it is seeing light emitted in the far more distant past as it arrives here now.

Russell

[Spikey]

Quite simply, we don't.

According to current theories nothing, but nothing, can travel faster than light. So the soonest that any info of it's death throes can reach us is the very same moment as the light from the event.

Sorry to be a bore but theoretically a Tachyon particle can travel faster than the speed of light.

[Nexus 6]

Sorry to be a bore but theoretically a Tachyon particle can travel faster than the speed of light.

ok you got me interested in that comment.

[Ad Astra]

Astrophysicists speak of "light cones" Draw a graph with time increasing on the vertical axis, and space horizontally. Place a dot on the graph to represent a star. Now draw an 'X' through the point, with the arms of the X at exactly 45 degrees. This is the light cone, or 'event horizon' of that star.

For any point inside the cone, it will receive light from the star sometime in the future, for any object outside the cone, the star effectively doesn't exist, because no information can ever get from the star to that object. Put another way, the expansion of space will keep that object forever beyond the 'event horizon' of that object - so nothing that happens to that star can ever affect the object outside the cone.

Take this to the extreme case, we know that the Universe' visual horizon is 13.7 billion light years away, and that light from an object that far distant has taken the entire lifetime of the Universe to reach us. But if you consider that 1. all of space has been expanding, and 2. the inflationary theory of the early Universe (Alan Guth, et al) there must have been some stars that formed far enough away from us that the light will never get here. Astrophysicists calculate that the true extend of the Universe must be at least 1x10e80 light years in diameter, (a 1, followed by 80 zeros) and according to some theorists, up to 1x10e500 LY in diameter. (Gribben, Deutsch, Hawking, Penrose, Tippler, et al).

I can highly recommend the following reading if you want to pursue this: (no calculus, I promise!!!)

The Grand Design, Hawking & Mlodinov

The Universe in a Nutshell, Hawking

In Search of the Multiverse, Gribben

The Fabric of Reality, Deutsch

The 4% Universe, Panek

A Journey through Gravitation and Spacetime, Wheeler (awesome!!!)

Cheers,

Dan

[rowan46]

Sorry to be a bore but theoretically a Tachyon particle can travel faster than the speed of light.

As far as I understand ( which isn't much) it's a hypothetical particle with no experimental evidence that it exists at all and whats more if it did exist we would have no real way of proving, it as it can't exist in our relativistic universe where nothing can go faster than light. we would have no way of measuring something whose bottom speed was faster than light. I think ( I don't really understand physics)

[Ad Astra]

As far as I understand ( which isn't much) it's a hypothetical particle with no experimental evidence that it exists at all and whats more if it did exist we would have no real way of proving, it as it can't exist in our relativistic universe where nothing can go faster than light. we would have no way of measuring something whose bottom speed was faster than light. I think ( I don't really understand physics)

Quite correct. The tachyon was an interesting idea, but no such particle occurs in the modern standard model of particle physics, nor does it occur in string theory, or any modern cosmological theory that I know of.

On the flip side, modern inflationary theory says that space can expand faster than the speed of light, but particles of matter or quanta of energy moving through spacetime are restricted to that speed, and no greater is allowed.

Dan

[jamespels]

To add to Ad Astra's list, I can highly recommend "a very special relativity" by Sander Bais. No maths, and uses light cones as described by Dan to explain special relativity. Don't expect an easy read - this is not a simple subject - but once you get your head around the concepts involved the book gives the first explanation I have been able to follow.

Thanks for the list, Dan - I am already looking forward to going through them.

[wiseman]

If you have a powerful enough laser and shine it on one edge of the moon, it is possible to get the trace of the laser as you swing it through a few seconds of arc, to go faster than the speed of light as it speeds across the face of the moon, although no individual particle will break the speed of light limit.

[wiseman]

Also, if you are living on another planet 250 million light years away, and they have a special offer on that planet on 400 inch dobsonians, you will be able to train your scope on the earth, and see the Dinosaurs swanning around in the Jurrasic period.

We are doing the same thing when we look at the stars. Even light from the sun is 8 minutes old when we see it.

I always have a quick look up at Betelgeuse every night I am out, just in case it happens to go bang when I am looking at it. And thats without a telescope!

[iwatkins]

Not only are we seeing the light from possibly millions of years ago, but what will do your noggin in is that the stars you see are not where they are now.

Even the sun has moved on by over eight minutes by the time we see the light.

Best not to worry about it or your head will explode

Cheers

Ian

[Ad Astra]

If you have a powerful enough laser and shine it on one edge of the moon, it is possible to get the trace of the laser as you swing it through a few seconds of arc, to go faster than the speed of light as it speeds across the face of the moon, although no individual particle will break the speed of light limit.

Indeed no. A cornerstone of Einstein's relativity theory is that all observers measure the speed of light as the same. Also, you are forgetting that light is quantitized into photons. Think of it (the laser or torch) as a machine gun spitting out individual particles, not a continuous beam. Each particle moves along is a (relatively) straight line [actually, it follows the local geodesic, or local curvature of spacetime], and each particle moves at exactly light speed. The 'arc of the beam' you refer to isn't a material thing.

Dan

See J. Wheeler's book from the above list for an excellent explanation of this...

[RobH]

'Now' is a concept that only works locally, and is pretty meaningless on large scales.

[Diddydo75]

This is why I have been interested in this Astronomy for so long, its not just the looking its the wondering why!

[wiseman]

@ad astra.

Thats why I posted although no individual particle will break the speed of light limit. The trace of the beam, may not be material, but it is observable, and measurable, it doent berak any laws, its just an interesting theroretical phenomenon

[Earl]

I like the fact that when you look in the skies all that light is from different times.