

Gravitational lens magnifies earliest galaxy yet seen - Reltair
http://arstechnica.com/science/2012/11/gravitational-lens-magnifies-earliest-galaxy-yet-seen/

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iwwr
Speaking of gravitational lenses, our very own sun can be used as one:

<http://www.centauri-dreams.org/?p=22321>

Key facts:

can work with existing technology

$5bn cost

long travel time, a century or so to the primary observation point (500-750au)
but can visit several distant icy bodies before that point

100x magnification for infrared and visible-light (50-80x for radio and
microwave) (only for object directly opposite the sun though)

a good precursor for an interstellar mission and

good study platform for the interstellar medium

~~~
stargazer-3
110 years to reach primary mission point? I'd say that we ought to spend more
time on rocket engine studies before launching something like this. Besides,
100x magnification still wouldn't help us to resolve an Earth-like planet.

~~~
Groxx
For 110 years, I suspect we'd be better off simply creating a larger lens
array somewhere nearby in space. Might not be cheaper, but would probably be
more valuable in the meantime.

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andrewcooke
paper - <http://arxiv.org/pdf/1211.3663v1.pdf> (the link and redshift, 10.8,
are just under the image).

it's a photometric redshift derived from the lyman break. rest-frame ultra-
violet emission less than 912 A is "completely" absorbed by intervening
neutral hydrogen, and between 912 and 1216 A partially, in lines. so objects
are dark at shorter wavelengths than 1216 A (in the frame of the galaxy).
their observations show that in our frame there's no emission short of 1.46 um
(infra-red). and 1.46e-6 / 1216e-10 ~ 12 = 1+z, so redshift is approx 11.

if it's correct (photometric redshifts are not as reliable as those obtained
from spectra, but are technically easier to achieve, and this is really
pushing the limits of what is possible - my partner, who is still in
astronomy, is sceptical that this is real), then it's the most distant object
known.

i guess the above isn't very clear. i'll try again. hydrogen gas just floating
around in space absorbs ultra-violet (UV) light. so you don't see much UV from
galaxies.

now distant galaxies are redshifted so much (by expansion of the universe)
that the UV ends up in the infra-red (IR). so what you observe are things that
are only visible in the IR - everything shorter (optical and UV) in our frame
was absorbed (UV) in the galaxy's frame.

so one way to find extremely distance objects is to find things that can only
be seen in the IR. what you're actually seeing is the redshifted optical; what
you don't see in the optical is what, in the galaxy's frame, is absorbed UV.

but these galaxies are very faint, so they are hard to detect. using a
gravitational lens boosts the brightness and so makes this technique more
powerful.

i'm not sure that helps (a diagram would make things much clearer). the
technique, well, the resulting objects, are called "lyman break galaxies". but
i haven't found a good reference googling.

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Aardwolf
Isn't that awesome, the galaxy is huge, our planet is tiny, and yet all the
objects in the whole galaxy have photons that reach our little planet, the
lens of that specific telescope even. The photons traveled that far, that
long, just to be finally absorbed by that telescope. What are the chances of a
photon from an object that far away to hit specifically this location?

~~~
gus_massa
The surface of the sphere of the light that is traveling since an event "soon"
after to the big bang is (4 * pi * (15000000000 lightyears)^2) (I don't know
how to handle the space expansion, so I will simply ignore it.)

The surface of the main mirror in the Hubble Telescope is (pi * (2.5
meters)^2)

The gravitational lens gives a 8x magnification, so the telescope picks 8^2
times the light (not sure about this ^2).

So, the (approximated) probability that a photon reach the telescope is: (pi *
(2.5 meters)^2) * (8^2) / (4 * pi * (15000000000 lightyears)^2)~=5E-51

[http://www.google.com/?q=(pi*(2.5%20meters)%5E2)%20*%20(8%5E...](http://www.google.com/?q=\(pi*\(2.5%20meters\)%5E2\)%20*%20\(8%5E2\)%2F%20\(4*pi*\(15000000000%20lightyears\)%5E2))

So, it had to be a very bright object! Or saying it in another way
<http://xkcd.com/811/>

~~~
ctdonath
A flippant googling suggests the Sun outputs 10^45 photons per second. The
very bright object in question is a galaxy consisting of, we can presume, a
few orders of magnitude more than 10^6 stars. Upshot is that the Hubble
Telescope should be receiving a few hundred or thousand photons from that
galaxy every second.

In comparison and for scale, IIRC the human eye has been shown capable of
detecting individual photons.

