Gravity Lens Telescope performance?

[UmbralRaptor]

The idea of using the sun's gravity as a telescope has been fairly developed, but I've been having lots of trouble finding details. (Besides how to get a probe there)

Playing around with the simplified version for a point mass gets me the numbers (in terms of just under 550 AU minimum distance and ~1.5 arcsecond apparent size of the image ring) that jibe with what's found elsewhere, but I still have lots of interrelated questions: What is the width (linear and angular) of the ring? (I assume it depends on the nature of the imaging system?) How much is the image magnified and/or made brighter? Is the image ring always ~1-1.5 solar diameters for the typical 550-1000 AU distances, no matter how distant the object being magnified is? If so, does this make it unsuitable for observations of distant galaxies? Can this work for more distant stars, and if so, why isn't it already in use given that there are a number of distant (non-trivial redshift) galaxies with annoying foreground stars? And how do you deal with the sun being right in the middle of your image? A coronagraph?

I suppose it's mostly a big mess of general relativity and optics that I don't have much familiarity with. Hence this being tagged as Physics instead of Sci Fi Theory.

edit: Found a

, and a frustratingly expensive book that likely has lots of details. Edited July 19, 2015 by UmbralRaptor
more info, I guess.

[Sampa]

I'm actually familiar with this idea...not enough to provide any important stuff, though

[YNM]

A limiting case would be your distance from the Sun. Unlike standard glasses, lens, and mirrors, focus points vary both from angular distance (seen from your site) and linear distance from main object (Sun). There's a formula but I need to search it first.

[Xannari Ferrows]

I believe you are after Dawes' limit. The accuracy of all cameras has a limit on the number of radians it can nail down at a time, to put it simply.

[AngelLestat]

but I've been having lots of trouble finding details. (Besides how to get a probe there)

Yeah I hear about using the sun as gravitational lense 5 years back, but never in so much detail as is explained in the video.

I dont know about optics, but in the video seems very well explained.

Although the presentation is quite outdated with some info.

For example, they already found planets in alpha centaury system, so maybe they would not need 1 million km tether to map the whole system, if we know the exact position wherem the planet will be at some moment, then we can map just that part of the system.

About how to get there.. the best way would be solar sails, not with current solar sails materials as kapton or mylar, they will need to use CNT.

The benefics of solar sail is the high speed that you can achieve and you can use the solar sails as a big parabolic to focus your comunications with earth. If you have a telescope, you will need to transfer a lot of data.

But visualize the black hole in the center of the galaxy seems also a very good target.

[Aethon]

From: Black Holes: Attractors for intelligence? :

"At 22.45AU and 29.59AU we have a focus for gravitational waves and neutrinos*. Starting from 550AU, electromagnetic waves converge. Those focus regions offer one of the greatest opportunity for astronomy and astrophysics, offering gains from 2 to 9 orders of magnitude compared to Earth-based telescopes. Over the years, Claudio Maccone (2009) has detailled with great technical precision such a scientific mission, called FOCAL. It is also worth noting that such gravitational lensing could also be used for communication. If we want to continue and improve our quest for understanding the cosmos, this mission is a great opportunity to complete our fuzzy astronomy with a focused one. In other words, the time may be ripe to put on our cosmic glasses."

*because gravitational waves and neutrinos can pass through the sun.

http://arxiv.org/ftp/arxiv/papers/1104/1104.4362.pdf

http://link.springer.com/chapter/10.1007%2F3-540-54752-5_236

^^ This is behind a pay wall but will save you $130 over the price of Maccones' book.

"Jupiter is the most massive planet, and we find that its focal sphere is about 1.1 light months out, or 6100 AU. That’s a useful number to remember, because it’s always possible that the Sun’s coronal effects may distort what we’re trying to look at on the other side of the Sun."

"Remarkably, the focal sphere of the Earth is found at 15,375 AU, closer than the focal sphere of Uranus, the point being that Earth is the body with the highest density (ratio of mass to volume) in the entire Solar System. Getting to the Earth’s gravitational lens would be useful because we know the composition of our planet’s atmosphere and surface better than that of any other planet. We would thus have maximum data for using its lens for observations."

Centauri dreams

http://www.centauri-dreams.org/?p=15290

http://uavarese.altervista.org/CM_Interstellar_Radio_Links.pdf

http://www.kiss.caltech.edu/study/science/FOCAL%20Mission%20Concept%20JOHNSON.pdf

Edited July 19, 2015 by Aethon

[YNM]

@AngelLestat : Planetary discovery nowadays mostly are just the same with spectroscopic double star disvovery, via shifting of spectrum and not direct imaging. α Cen Bb is discovered this way (making a good spectograph is more achievable than making huge telescopes). A very stupendously large telescope is needed for that, or the planet will be quite far from the parent star. Visualizing Milky Way's black hole would be more a matter of extinction and scattering, as it already able to be somewhat mapped in infrared and high energy photons (UV, X ray, gamma ray).

For my promise : I'll have to wait for next day, typing from phone isn't the best way to embed pictures as I'm away... Anyway, your question is exactly the same as a one of the theoretical problem in 1st IOAA 2007 ! Maybe you can grab the solve and look it up.

[UmbralRaptor]

I believe you are after Dawes' limit. The accuracy of all cameras has a limit on the number of radians it can nail down at a time, to put it simply.

I'm not comfortable throwing around things like the Rayleigh Criterion here, given the differences between gravitational lenses and normal lenses/mirrors.

For example, they already found planets in alpha centaury system, so maybe they would not need 1 million km tether to map the whole system, if we know the exact position wherem the planet will be at some moment, then we can map just that part of the system.

The detections are still not quite guaranteed, and we could have missed some. But certainly it would ease the amount of sky needed to scan.

I'm not going to touch propulsion issues at the moment.

But visualize the black hole in the center of the galaxy seems also a very good target.

Likewise, though I would expect ground based competition.

http://arxiv.org/ftp/arxiv/papers/1104/1104.4362.pdf

http://link.springer.com/chapter/10.1007%2F3-540-54752-5_236

^^ This is behind a pay wall but will save you $130 over the price of Maccones' book.

Thanks. I'll have to see if I have institutional access, but since this is mainly out of curiosity, it's probably not worth putting actual money into.

[AngelLestat]

"At 22.45AU and 29.59AU we have a focus for gravitational waves and neutrinos*. Starting from 550AU, electromagnetic waves converge. Those focus regions offer one of the greatest opportunity for astronomy and astrophysics, offering gains from 2 to 9 orders of magnitude compared to Earth-based telescopes. Over the years, Claudio Maccone (2009) has detailled with great technical precision such a scientific mission, called FOCAL. It is also worth noting that such gravitational lensing could also be used for communication. If we want to continue and improve our quest for understanding the cosmos, this mission is a great opportunity to complete our fuzzy astronomy with a focused one. In other words, the time may be ripe to put on our cosmic glasses."

It seems interesting if we point to some binary black hole or BH and neutron star in this galaxy, or some other massive objects in different galaxies. But there is a problem.

neutrino detectors are very heavy, so all you gain in magnitud, you lost it at chance to detect them, but is a great idea to study neutrinos comming from a single target, and not from the whole universe.

About gravity waves, is also very complex, but sounds good.

@AngelLestat : Planetary discovery nowadays mostly are just the same with spectroscopic double star disvovery, via shifting of spectrum and not direct imaging. α Cen Bb is discovered this way (making a good spectograph is more achievable than making huge telescopes). A very stupendously large telescope is needed for that, or the planet will be quite far from the parent star. Visualizing Milky Way's black hole would be more a matter of extinction and scattering, as it already able to be somewhat mapped in infrared and high energy photons (UV, X ray, gamma ray).

For my promise : I'll have to wait for next day, typing from phone isn't the best way to embed pictures as I'm away... Anyway, your question is exactly the same as a one of the theoretical problem in 1st IOAA 2007 ! Maybe you can grab the solve and look it up.

I know, but we are not talking about using this to just discover new planets... with that magnitud increase, we would be able to see the planet without the incomming light of its star.

So we can learn a lot more on that planet to the point of know its true value as destination.

What you mean by extinction and scattering? If we would be able to see the horizon, that is the 100% proff that black holes exist, and analizing the light distortion finger print, it would tell us a lot about its nature..

Rotation speed, gravity variations and compare all that with our predictions.

Likewise, though I would expect ground based competition.

Not sure, those are 2 very different techniques.

[YNM]

I know, but we are not talking about using this to just discover new planets... with that magnitud increase, we would be able to see the planet without the incomming light of its star.

So we can learn a lot more on that planet to the point of know its true value as destination.

What you mean by extinction and scattering? If we would be able to see the horizon, that is the 100% proof that black holes exist, and analizing the light distortion finger print, it would tell us a lot about its nature..

Rotation speed, gravity variations and compare all that with our predictions.

For planets, you'll be in the wrong wavelength, or that it'll be so weak that the magnitude will be very low. Even if those are not problem at all, you'll need some super-high-res detector with super-tiny pixel size - a gravity lens doesn't have any applicable aperture (and so no resolution power). Or a large telescope, which would be a waste.

For black hole of Milky Way, still the same - you'll need some goodly resolving things.

Likewise, though I would expect ground based competition.

Not sure, those are 2 very different techniques.

More applicable to me, considering the fact that they're there already. Just a matter of timing (when all the 'scope / dish can view the object).

--------

So, now, my (copy and paste) answers :

(important assumption - all angles are very small)

You can fiddle around to get the deflection parameter. I'll try to calculate some things with it first.

EDIT :

The results, for an infinitely distant object located behind the lensing object, gives a minimum distance from Sun as ~550 AU, where the Einstein Ring / Cross will be located at the rim of the Sun's disk from that distance. The angular diameter of this ring/cross will be 1.69E-5 radians (for comparison, HST resolving power is 2.42E-7 radians). Not to mention things like corona and such. So I should say that this thing is going to be expensive anyway, and it'd still be better to get a lot of dish on ground.

Edited July 21, 2015 by YNM