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Author Topic: Hubble Telescope Spots Gravitationally-lensed Supernova  (Read 4860 times)

Telecaster

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Hubble Telescope Spots Gravitationally-lensed Supernova
« on: March 05, 2015, 05:57:51 pm »

IMO this is pretty nifty: a background supernova magnified & duplicated, in an "Einstein Cross" configuration, by the gravitational warping of a foreground galaxy.

http://hubblesite.org/newscenter/archive/releases/2015/08

Also nifty is the prediction that within the next five years we'll see additional versions of the same supernova due to some of its light taking longer paths to reach us.

-Dave-
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Ray

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #1 on: March 05, 2015, 11:11:48 pm »

Interesting! However, I must admit I can't fathom what's going on here, perhaps because I'm not an astrophysicist.

I understand the concept that a part of the light leaving the supernova might take different paths and will arrive at the observer on planet earth, or at the Hubble Telescope orbiting the earth, at different times. But surely, whatever the number of different paths the light takes, and whatever the differences in the time that part of the light takes to reach us, there is only one continuous and uninterrupted stream of photons arriving at the position of the observer. There is only one image at any given instance. If that 'apparently' single image in reality consists of multiple images, wouldn't it just be blurred, and/or subject to various color aberrations? 

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Astronomers using NASA's Hubble Space Telescope have spotted for the first time a distant supernova split into four images. The multiple images of the exploding star are caused by the powerful gravity of a foreground elliptical galaxy embedded in a massive cluster of galaxies

The supernova's various light paths are analogous to several trains that leave a station at the same time, all traveling at the same speed and bound for the same location. Each train, however, takes a different route, and the distance for each route is not the same. Some trains travel over hills. Others go through valleys, and still others chug around mountains. Because the trains travel over different track lengths across different terrain, they do not arrive at their destination at the same time. Similarly, the supernova images do not appear at the same time because some of the light is delayed by traveling around bends created by the gravity of dense dark matter in the intervening galaxy cluster.
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Johnny_Johnson

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #2 on: March 05, 2015, 11:21:30 pm »

Ray, Google gravitational lensing. The concept has been around, and observed, for a number of years.

Later,
Johnny
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fdisilvestro

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #3 on: March 06, 2015, 12:55:57 am »

whatever the number of different paths the light takes, and whatever the differences in the time that part of the light takes to reach us, there is only one continuous and uninterrupted stream of photons arriving at the position of the observer. There is only one image at any given instance.


You are thinking in light following a straight line. Here the "lines" are being bent by a strong gravitational field and images that should originally be aimed at different observers are now diverted to the same observer

Ray

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #4 on: March 06, 2015, 05:28:30 am »

You are thinking in light following a straight line. Here the "lines" are being bent by a strong gravitational field and images that should originally be aimed at different observers are now diverted to the same observer

How could I be thinking that light travels in a straight line when I've already stated that I understand the concept that the light can take different paths? If light were to travel in a straight line there could be only one path, a straight path to the observer.

What I'm having difficulty understanding is how the different images, resulting from different paths of light from the same source, can be disentangled. At any given instance, the light from all paths will be observed as part of the same image.
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NancyP

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #5 on: March 06, 2015, 01:38:27 pm »

I am pretty sure that the maths involved is above my pay grade....   ???
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amolitor

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #6 on: March 06, 2015, 01:50:06 pm »

You are conflating "lens" with "well designed lens"

Look at something in your home, say, a light, through various glass objects you have lying around. Glasses, jars, etc. It should not take you long to start observing multiple, variously distorted, images of the light simultaneously. Then consider what's actually going on.
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Ray

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #7 on: March 06, 2015, 06:32:08 pm »

You are conflating "lens" with "well designed lens"

Look at something in your home, say, a light, through various glass objects you have lying around. Glasses, jars, etc. It should not take you long to start observing multiple, variously distorted, images of the light simultaneously. Then consider what's actually going on.


No. I'm assuming the lens is well-designed. Whatever the multiple paths the light takes, I imagine that the observed source , depending on the variation in the angle of light reaching the observer, will appear either as a duplicate image, such as a twin star, or partially merged images, and sometimes completely merged images.

A frequently used analogy on the internet is to describe the process as similar to two trains or two cars taking different routes and arriving at their destination at different times. However, it seems to me that such an analogy is more appropriate to describe the paths of just two single photons.

The reality is, whatever the path taken, there is a continuous stream of photons arriving every nanosecond. Train or car crashes would be frequent, surely.
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amolitor

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #8 on: March 06, 2015, 06:35:09 pm »

The lens in question here is gravitational. It's formed by great masses slopped about the universe without any input whatsoever from the designers at Nikon and Zeiss.

It's a lot more like a random blob of glass than it is like a camera lens. Again, look at a light through some random glass objects you have lying around the house.
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Ray

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #9 on: March 06, 2015, 06:57:01 pm »

The lens in question here is gravitational. It's formed by great masses slopped about the universe without any input whatsoever from the designers at Nikon and Zeiss.

It's a lot more like a random blob of glass than it is like a camera lens. Again, look at a light through some random glass objects you have lying around the house.


Well put, but I'm not questioning the effects of gravity in bending light but the mind-bogglingly difficult task of correcting these misshapened, distorted images, and being certain that the correction is correct and that the object's position in the universe is correct. There must be huge uncertainty here.
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amolitor

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #10 on: March 06, 2015, 07:02:36 pm »

Oh, I see!

Yeah, it's not obvious to me that it's even possible. You sort of can't see the dark matter after all, right? That being more or less the definition?

Possibly they can make some estimates based on.. something having to do with the lensing of a bunch of different objects about which you know.. things. Statistical things, perhaps?
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Telecaster

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #11 on: March 08, 2015, 03:59:58 pm »

The latest Science Friday on NPR starts with a discussion of general relativity and includes mentions of gravitational lensing and the "Einstein Cross" supernova image captured by Hubble. Also includes an audio snippet of Einstein describing science as what it fundamentally is: not a body of knowledge but a method.

http://www.sciencefriday.com/audio/#page/full-width-list/1

-Dave-
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Ray

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #12 on: March 08, 2015, 09:19:42 pm »

What I find quite fascinating about this Einsteinian model of the universe, and also quite amusing, is the nature of the 'Cosmological Constant', which Einstein added to his equations for General Relativity.

A huge problem with Isaac Newton's theory of gravity was how to provide a satisfactory explanation as to why the universe was not collapsing upon itself if every star and planet was subject to a force of gravitational attraction.

As I understand, Newton's only explanation was that 'God' prevented this from happening. Newton was very religious, although in an unorthodox way.

Einstein accepted this Newtonian view of a static universe and must have been very puzzled when his equations for General Relativity implied that the universe is expanding. To negate the effect of such an expansion he introduced a Cosmological Constant into his equations.

A few years later, in 1929, Edwin Hubble provided convincing evidence that the universe really is expanding, so Einstein removed his Cosmological Constant, the introduction of which he later described as the greatest blunder in his career, since his initial equations without the Constant were predicting that the universe should be expanding, which later proved to be true.

However, as a result of recent observations that imply the universe is expanding at an accelerating rate, the Cosmological Constant has to be reintroduced, although with a different value. If Einstein were still alive, he could declare, "Hey! It wasn't my biggest blunder. I just got the value a bit wrong."  ;D
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Telecaster

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Re: Hubble Telescope Spots Gravitationally-lensed Supernova
« Reply #13 on: March 09, 2015, 06:21:00 pm »

A few years later, in 1929, Edwin Hubble provided convincing evidence that the universe really is expanding, so Einstein removed his Cosmological Constant, the introduction of which he later described as the greatest blunder in his career, since his initial equations without the Constant were predicting that the universe should be expanding, which later proved to be true.

However, as a result of recent observations that imply the universe is expanding at an accelerating rate, the Cosmological Constant has to be reintroduced, although with a different value. If Einstein were still alive, he could declare, "Hey! It wasn't my biggest blunder. I just got the value a bit wrong."  ;D

Just to note, the phrase greatest blunder is actually a partial misquote of the physicist George Gamov, who once said that Einstein "remarked that the introduction of the cosmological term was the biggest blunder he ever made." AFAIK Einstein himself never made any public comment about it. Recently, yes, the term has been invoked as a possible way to account for "dark energy," at least within the equations of general relativity, thus possibly vindicating the term to some extent. We shall seeā€¦

-Dave-
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