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Comment by BSOhealth | Hacker News Reader

With all the lensing going on out there, is it possible for us to observe the light from our sun (and potentially our planet) billions of years ago?

A cool achievement would be, observe the moon/earth separation event(s)

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Theoretically yes but although this black hole is big enough to make that more realistic, the redirected light would be have lost so much energy we’d likely be unable to observe it. We’d need an orbital hypertelescope to even stand a chance. Even then we wouldn’t see the earth because it would be drowned out by the sun.

The bigger problem is all the dust and other stars in the way. I’m not aware of any black holes close enough that would have a direct path for the light to cross without being absorbed and scattered.

The other problem is the angle at which the light must be redirected. The Cosmic Horseshoe is composed of two systems almost directly in line, the light comes from the farther system and bends infinitesimally around the black hole to come to us. I don't know if a 180 degree bend is possible.

Also, the foreground galaxy/supermassive black hole in the Cosmic Horseshoe is 5.6 billion light years away, so any light that could come from our solar system, go around the black hole, and come back to our hypothetical hypertelescope would be over 11 billion years old - almost triple the age of our sun.

Saggitarius A* in our own galaxy is, of course, directly in the elliptic and therefore badly occluded by dust, but it would be interesting to look at as it's only 27k light years away. In the absence of that pesky dust, it would give us a picture of the solar system as of the Paleolithic. Andromeda, at 2.5 million light years away, would give us 5-million-year-old light. There are other black holes in the Milky Way on the order of a thousand light years away which are not at the center of the galaxy but have masses comparable to or slightly larger than our sun, these are far closer (within a few thousand years) but have much smaller gravitational fields. Luminous intensity drops off with the square of the distance, but I'm not sure how the gravitational field strength affects the ability of a particular galaxy to bend light.

> The other problem is the angle at which the light must be redirected. The Cosmic Horseshoe is composed of two systems almost directly in line, the light comes from the farther system and bends infinitesimally around the black hole to come to us. I don't know if a 180 degree bend is possible.

It is possible to get a deflection angle of 180 but under a few million solar masses, hitting the “sweet spot” in between the photon sphere and the boundary of the shadow would basically be a once in the lifetime of the universe type probability, if it were possible at all. At billions of solar masses that sweet spot become much bigger, but then those are much further away.

> almost triple the age of our sun.

In this insanely hypothetical scenario, would it be possible to see a sun before our sun? (In the same galactic vicinity)

I was under the impression that our sun is not large enough to form the heavier elements on earth and this means supernova or collision of neutron stars had to be responsible for creating these elements, some of the stuff flying off this explosion formed our solar system, so we could see those progenitor stars.

I thought elements were created inside stars and dispersed by supernovas... Our sun has clearly not exploded yet (and I don't think it's big enough to ever ho supernova), so why does it matter what elements it can create?

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