[HN Gopher] Two galaxies aligned in a way where their gravity ac...
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Two galaxies aligned in a way where their gravity acts as a
compound lens
Author : wglb
Score : 147 points
Date : 2024-11-16 16:48 UTC (6 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| wglb wrote:
| This is seriously cool. One lens galaxy is amazing, but two! (Too
| bad that this is not steerable.)
|
| Underlying paper: https://arxiv.org/abs/2411.04177
| travisporter wrote:
| Cool! Was hoping to see a magnification amount like 100x etc
| hinkley wrote:
| It would be cool if we some day had special days of astronomy
| where every telescope is turned to galactic eclipses the way
| they once did for solar eclipses.
|
| The sky is huge and we are moving, so surely some would happen
| in our lifetimes?
| yreg wrote:
| Surely any such eclipse lasts a long time. From the
| perspective of our lifetimes it is static.
| photonthug wrote:
| So they were looking in the neighborhood, basically found light
| sources that looked like they might be duplicates and they were,
| therefore lensing.
|
| Can we then find more lensing with even more compounding on
| purpose instead of accidentally if we sift existing data for such
| dupes?
| ck2 wrote:
| Fund the SGL Telescope!
|
| https://www.universetoday.com/149214/if-we-used-the-sun-as-a...
|
| Seriously, we could build that, it's at the limit of our tech but
| if it was either we walk on the moon again or build SGL, I'd pick
| SGL
| dmix wrote:
| I made this comment before but someone on HN made a good
| argument is way harder than it sounds and given it's
| size/cost/function it'd basically have to point in one
| direction, it's not like an easily moveable telescope you can
| scan around with.
| skykooler wrote:
| Yeah, you basically need to launch a new one for every target
| you want to image.
| Tomte wrote:
| Probably even many, because it's energetically impractical
| to stop at the focal point.
| Voultapher wrote:
| I'd think to make it practical you'd have to have kind of
| (semi-) automatic space based assembly infrastructure that
| builds them and launches them. Launching these probes
| individually seems like it would be impractical. Building
| that infrastructure wouldn't be easy at all and I don't see
| that happening in the next 50 years.
| ck2 wrote:
| "way harder than it sounds" is how we move forward
|
| walking on the moon was beyond our limits when it was
| announced
|
| JWST was insanely hard and almost cancelled a few times, look
| at it now
| moralestapia wrote:
| >we move forward
|
| Do you work in something related to Astro?
| dleary wrote:
| This is true, but also, keep in mind that the JWST was
| insanely hard and almost cancelled a few times :)
|
| The SGL would be much, much harder than the JWST would be,
| and the JWST was already stretching our capabilities.
|
| The SGL needs to be 650AU away from us. Voyager 1 and 2 are
| currently 165AU and 120AU away.
|
| The JWST is 0.01 AU from us.
|
| And you can only look in one direction after the probe
| finally gets into position. Once you're 650AU away, it's
| not really feasible to move "sideways" far enough to look
| at something else.
| munchler wrote:
| > the finding will allow other researchers to more precisely
| calculate the Hubble constant
|
| How would a compound lens lead to a better estimate of the
| expansion rate of the universe?
| mafuyu wrote:
| From the abstract:
|
| > This unique configuration offers the opportunity to combine
| two major lensing cosmological probes: time-delay cosmography
| and dual source-plane lensing since J1721+8842 features
| multiple lensed sources forming two distinct Einstein radii of
| different sizes, one of which being a variable quasar. We
| expect tight constraints on the Hubble constant and the
| equation of state of dark energy by combining these two probes
| on the same system. The z2=1.885 deflector, a quiescent galaxy,
| is also the highest-redshift strong galaxy-scale lens with a
| spectroscopic redshift measurement.
| magicalhippo wrote:
| Not an expert, just trying to add some more context.
|
| With time-delay cosmography[1] one exploits that unless the
| source is perfectly in the center of the line of sight, then
| the photons that make up one lensed copy have traveled a
| different distance from the source than photons that make up
| a different lensed copy. This effect can be used to measure
| absolute distance and give an accurate measure of the Hubble
| constant.
|
| With dual source-plane lensing[2] one exploits that if two
| different sources lensed by the same lens, one can take the
| ratio of the measurements between the two sources and get
| results that are significantly less affected by the lens
| itself and is completely independent of the Hubble constant.
|
| [1]: https://arxiv.org/abs/2210.10833
|
| [2]: https://arxiv.org/abs/2204.03020
| dleary wrote:
| Disclaimer: I am a layman, not trained at all. But I am
| interested in this stuff.
|
| Our most powerful telescopes can see "back in time", by looking
| at stuff far enough away that it took nearly the entire age of
| the universe for the light to reach us.
|
| I would guess that we can use this natural compound lens to
| "see farther" with our current telescopes than we might
| otherwise be able to see.
|
| Our current best telescope, the JWST, can almost see to the
| very beginning of when it was possible to see, somewhere
| between 300k and 200M years after the big bang [0].
|
| Somewhere in this time period, the universe cooled enough for
| normal matter to form.
|
| The JWST still cannot see the actual 'edge' of when this
| occurred.
|
| Maybe with this natural compound lens, we can see all the way
| to the edge.
|
| And if we could see where the edge actually is, then maybe we
| can refine the estimate to a tighter range than [300k,200M],
| which would give us a better estimate of the expansion rate of
| the earlier universe.
|
| [0] https://www.universetoday.com/168872/webb-observations-
| shed-...
| waltbosz wrote:
| One fun thing think about is that these two galaxies are only
| aligned from our perspective in the universe. Viewed from a
| different location, and they're just two normal galaxies.
|
| Also, imagine having the technology to send signals through the
| lens and get the attention of intelligent life on the other side.
| kcmastrpc wrote:
| I'm sure there are plenty of civilizations that have done this,
| but on the time scale of the universe no one happens to look at
| just the right moment.
| Voultapher wrote:
| But wouldn't the size and age of the universe also imply that
| _someone_ has looked at just the right moment somewhere
| somewhen.
| drexlspivey wrote:
| Don't radio waves weaken proportionally to the square of
| the distance? No one would be able to detect them past a
| (relatively) small distance.
| shagie wrote:
| Omnidirectional source, yes.
|
| However, beamed sources don't fall off that way.
|
| A search for optical laser emission from Alpha Centauri
| AB -
| https://academic.oup.com/mnras/article/516/2/2938/6668809
|
| > ... This search would have revealed optical laser light
| from the directions of Alpha Cen B if the laser had a
| power of at least 1.4-5.4 MW (depending on wavelength)
| and was positioned within the 1 arcsec field of view
| (projecting to 1.3 au), for a benchmark 10-m laser
| launcher
|
| For comparison, with our measly human technology...
|
| https://www.ukri.org/news/uk-science-facility-
| receives-85m-f...
|
| > The Vulcan 20-20 laser is so named because it will
| generate a main laser beam with an energy output of 20
| Petawatts (PW) alongside eight high energy beams with an
| output of up to 20 Kilojoules (KJ). This is a 20-fold
| increase in power which is expected to make it the most
| powerful laser in the world.
|
| Or even five decades ago (TODAY!) ...
| https://en.wikipedia.org/wiki/Arecibo_message
|
| > The entire message consisted of 1,679 binary digits,
| approximately 210 bytes, transmitted at a frequency of
| 2,380 MHz and modulated by shifting the frequency by 10
| Hz, with a power of 450 kW.
|
| https://www.seti.org/seti-
| institute/project/details/arecibo-...
|
| > The broadcast was particularly powerful because it used
| Arecibo's megawatt transmitter attached to its 305 meter
| antenna. The latter concentrates the transmitter energy
| by beaming it into a very small patch of sky. The
| emission was equivalent to a 20 trillion watt
| omnidirectional broadcast, and would be detectable by a
| SETI experiment just about anywhere in the galaxy,
| assuming a receiving antenna similar in size to
| Arecibo's.
| quantadev wrote:
| The energy density drops off as inverse square law, but
| the photons go forever. Radio is just photons (light) so
| it goes forever until it interacts with something it
| hits. The expanding universe will stretch it's wavelength
| slightly however.
| snakeyjake wrote:
| In order to use them as a signaling platform (how?) the signal
| would have needed to have been sent several billion years ago.
|
| At 10 billion light years away from the most distant lens it is
| 100% certain that they are no longer in a gravitational lensing
| configuration.
|
| For a frame of reference, the Milky Way will be in the middle
| of its epic merger with Andromeda in about 5 billion years.
| buran77 wrote:
| Even assuming a civilization can predict the alignment of the
| lenses (galaxies), they'd still need quite a powerful signal
| just to reach the first lens, let alone the second, and then
| a potential civilization who may be listening at just the
| right time on the other side. Hard to beat background noise
| even at distances of a few light years.
| rjurney wrote:
| It's kind of interesting in terms of analytics... can we
| predict when lenses will appear and disappear, from our
| perspective? What might we do with that information once we
| are more advanced?
| augusto-moura wrote:
| And technically they are only temporarily so, given enough
| millions of years they will drift apart and lose the alignment.
|
| Also, other stars can come to align in the future. Makes me
| wonder if we can antecipate other cases like this and create a
| future schedule of "To Observe" so future generations can look
| at them. Although, these generations might be so distant from
| ours that might not even be considered of the same species
| yreg wrote:
| Is it only one direction or does it work the same from the
| other side?
| M_bara wrote:
| Should work the other way too. Physics and symmetry:)
| ted_dunning wrote:
| Yes in a vague sense. And No in a strong practical sense.
|
| Lensing works in reverse except for time delays which make
| the idea much more complex. The object's past is projected
| to us now, but our past would be projected to somewhere
| that the far object no longer occupies. Double lensing
| makes this even less reversible.
|
| When the light we are now seeing was emitted, the lensing
| wasn't in place. In fact, the galaxies doing the lensing
| hadn't even evolved to the state that we see them in.
|
| So if we sent a response to what we see now, it wouldn't
| make it back to the lensed objects.
|
| That's just for single lensing. Double lenses are a massive
| coincidence of events at 4 points in time and space
| (emission, first deflection, second deflection and
| observation). That means that light going the other way
| wouldn't have the two intermediate points in the right
| place at the right times so it all breaks down for us and
| the object we see. There are some points that would be
| double lensed in the reverse direction but the locations
| and times for the source and observer have only very vague
| correlation to our location and the location of the object
| we see.
| quantadev wrote:
| A simpler answer is just what happens if you look thru a
| telescope or binoculars "the wrong way" (backwards). The
| correct way shows a "zoomed in" view of that you're
| viewing, but looking the wrong way shows a "zoomed out"
| view.
|
| So lifeforms on the other end of this cosmic "lens[es]"
| cannot use it to see us better, because in fact it makes
| us look further away from them than we are, from their
| perspective.
| dmead wrote:
| Thats probably not happening at that scale. I know this is the
| premise of interstellar communication in the three body
| problem. It's not real.
| jajko wrote:
| Not really, its premise is using our Sun, not some lens
| composed of 2 galaxies (that would probably misalign well
| before our signal would reach them), not sure how you came up
| with such an idea.
| dmead wrote:
| Using things at that scale to talk? It's not a thing in
| either case.
| bparsons wrote:
| If the lens curved light back toward us, could we see earth
| several million years ago?
| wizzwizz4 wrote:
| Technically? But the image would be very very very small, so
| we'd need a detector bigger than the solar system (guesstimate)
| to see it. That's to _see it_ : I can't imagine what it would
| take to _resolve_ the image. The tricks in this paper are a
| start.
| westurner wrote:
| To zoom into a reflection on a lens or a water droplet?
|
| From "Hear the sounds of Earth's magnetic field from 41,000
| years ago" (2024)
| https://news.ycombinator.com/item?id=42010159 :
|
| > [ Redshift, Doppler effect, ]
|
| > _to recall Earth 's magnetic field from 41,000 years ago
| with such a method would presumably require a reflection
| (41,000/2 = 20,500) light years away_
|
| To see Earth in a reflection, though
|
| Age of the Earth: https://en.wikipedia.org/wiki/Age_of_Earth
| :
|
| > _4.54 x 10^9 years +- 1%_
|
| "J1721+8842: The first Einstein zig-zag lens" (2024)
| https://arxiv.org/abs/2411.04177v1
|
| What is the distance to the centroid of the (possibly
| vortical ?) lens effect from Earth in light years?
|
| /? J1721+8842 distance from Earth in light years
|
| - https://www.iflscience.com/first-known-double-
| gravitational-... :
|
| > _The first lens is relatively close to the source, with a
| distance estimated at 10.2 billion light-years. What happens
| is that the quasar's light is magnified and multiplied by
| this massive galaxy. Two of the images are deflected in the
| opposite direction as they reach the second lens, another
| massive galaxy. The path of the light is a zig-zag between
| the quasar, the first lens, and then the second one, which is
| just 2.3 billion light-years away_
|
| So, given a simplistic model with no relative motion between
| earth and the presumed constant location lens:
| Earth formation: 4.54b years ago 2.3b * 2 = 4.6b years
| ago 10.2b * 2 = 20.4b years ago
|
| Does it matter that our models of the solar systems typically
| omit that the sun is traveling through the universe (with the
| planets swirling now coplanarly and trailing behind), and
| would the relative motion of a black hole at the edge of our
| solar system change the paths between here and a distant
| reflector over time?
|
| "The helical model - our solar system is a vortex"
| https://youtube.com/watch?v=0jHsq36_NTU
| DoingIsLearning wrote:
| @Dang is there a version of /best but for comments? The thought
| experiment in this comment broke my mind.
| slater wrote:
| https://news.ycombinator.com/highlights
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