5 ms·

Gravitational lens magnifies earliest galaxy yet seen

35 points by Reltair 14y ago

andrewcooke 14y ago
paper - http://arxiv.org/pdf/1211.3663v1.pdf 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.
iwwr 14y ago
Speaking of gravitational lenses, our very own sun can be used as one: http://www.centauri-dreams.org/?p=22321 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 14y ago
  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 14y ago
    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.
  - deleted 14y ago
    [deleted]
Aardwolf 14y ago
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?
- pavel_lishin 14y ago
  That specific photon? In hindsight, 100%. If you had to guess for any given photon, approximately 0%. But the odds that some photon would hit us is probably not too low.
- gus_massa 14y ago
  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%5E2)%2F%20(4*pi*(15000000000%20lightyears)%5E2 http://www.google.com/?q=(pi*(2.5%20meters)%5E2)%20*%20(8%5E...) So, it had to be a very bright object! Or saying it in another way http://xkcd.com/811/ http://xkcd.com/811/
  - ctdonath 14y ago
    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.
  - andrewcooke 14y ago

35 points by Reltair 14y ago

paper - http://arxiv.org/pdf/1211.3663v1.pdf 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.

iwwr 14y ago

Speaking of gravitational lenses, our very own sun can be used as one: http://www.centauri-dreams.org/?p=22321 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 14y ago
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 14y ago
  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.
- deleted 14y ago
  [deleted]

Aardwolf 14y ago

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?

pavel_lishin 14y ago
That specific photon? In hindsight, 100%. If you had to guess for any given photon, approximately 0%. But the odds that some photon would hit us is probably not too low.
gus_massa 14y ago
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%5E2)%2F%20(4*pi*(15000000000%20lightyears)%5E2 http://www.google.com/?q=(pi*(2.5%20meters)%5E2)%20*%20(8%5E...) So, it had to be a very bright object! Or saying it in another way http://xkcd.com/811/ http://xkcd.com/811/
- ctdonath 14y ago
  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.
- andrewcooke 14y ago