It is currently Fri, 15-12-17, 14:16 GMT

All times are UTC




Post new topic Reply to topic  [ 3 posts ] 
Author Message
PostPosted: Fri, 06-03-15, 12:22 GMT 
Offline
User avatar

Joined: Tue, 04-09-07, 2:32 GMT
Posts: 430
Location: South Korea
The special "General Relativity Turns 100" issue of Science has been published, and it has a rather interesting paper on gravitational lensing (quite an appropriate topic for this special issue).
Image

The paper is about the first discovery of time-delayed multiple images of a distant supernova.
An foreground galaxy is splitting light from this supernova into multiple mirages. This so-called Einstein cross has been observed before with quasars. What's new is that this time we are seeing not only a supernova in an Einstein cross, but we are also clearly seeing the mirages arriving at staggered time intervals.

Image
NASA, ESA, and A. Feild (STScI)

Why does this happen? Gravitational lensing distorts the path of light, and in doing so also slows it down in what's called the Shapiro Effect. The rate of slowdown differs according to the path taken, which is why a supernova can appear not only in different places, but at different times!

In fact not all of the mirages have arrived yet. The authors predict that light from the next mirage will arrive within the next ten years.

Here is the paper: http://arxiv.org/abs/1411.6009


Top
 Profile  
 
PostPosted: Fri, 06-03-15, 12:59 GMT 
Offline
Site Admin
User avatar

Joined: Fri, 31-08-07, 7:01 GMT
Posts: 4514
Location: Hamburg, Germany
Dawoon,

great that this amazing effect of GR has now been verified so nicely!

I knew about the effect before, notably since the time delays are inversely proportional to the Hubble constant, thus allowing to directly measure the expansion rate of the Universe. I think this was first predicted by Sjur Refsdal in the 60's (Refsdal, S., MNRAS, 1964, 128, 307; MNRAS, 1964, 128, 295, MNRAS, 1966, 134, 315).

I knew Refsdal actually in person, since he was Professor in Hamburg (Bergedorf observatory) for many years. He died in 2009 in Oslo, where he lived as an Emeritus after his retirement.

Do we have a chance integrating this into our gravitational lensing framework within celestia.Sci? What do you think? Probably, the distances involved must be larger than the galaxy distances we have available (10^9 ly)?

_________________
Image


Top
 Profile  
 
PostPosted: Sat, 07-03-15, 15:24 GMT 
Offline
User avatar

Joined: Tue, 04-09-07, 2:32 GMT
Posts: 430
Location: South Korea
It's unfortunate that Refsdal was not alive to see this remarkable observation..
As for implementing gravitational time delay in celestia.Sci, at the moment I don't know how to do it.
Currently the lensing code uses a fragment shader to distort only the current frame. To do time delay, the delayed fragments of the past would seemingly have to be recorded somewhere, to be played back at later time intervals. Since it is a) not easy to predict which fragments will need to be recorded, b) lensing could affect the whole frame, and c) several different past frames could contribute to the current frame, a naive implementation could thus be very storage intensive.

Even if the relevant past frames were to be computed on the fly, it could mean having to compute many past frames per frame, substantially bogging down the frame rate. To me, this problem seems similar to video compression, and perhaps some of the same compression tricks (wavelets, etc) could be used here also...


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group