10 ms·

Two galaxies aligned in a way where their gravity acts as a compound lens

271 points by wglb 2y ago

ziofill 2y ago
With all the galaxies out there, it seems likely that Earth should be in the focus of lots of systems of this kind. Hopefully in the future we'll be able to find and use these galactic telescopes!
wglb 2y ago
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 https://arxiv.org/abs/2411.04177
- travisporter 2y ago
  Cool! Was hoping to see a magnification amount like 100x etc
- hinkley 2y ago
  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 2y ago
    Surely any such eclipse lasts a long time. From the perspective of our lifetimes it is static.
    - hinkley 2y ago
      The farther away they are the slower they would scan the sky behind them or go out of conjunction. So I guess one of the objects would have to be something relatively close.
      - yreg 2y ago
        Are we not talking about galaxies? No galaxy is "close".
  - ben_w 2y ago
    Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way. The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years. So, unless you're even more optimistic about life extension technology than I am, not in our lifetimes, no.
    - vlovich123 2y ago
      > It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way. Relative to us. For the light itself it takes no time.
      - ben_w 2y ago
        Our own frame of reference is the only one that matters, given the comment I'm replacing to.
  - consp 2y ago
    Isn't the idea to use the sun as a lense already enough? The main problem being the focal point at 500+ au.
photonthug 2y ago
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 2y ago
Fund the SGL Telescope! https://www.universetoday.com/149214/if-we-used-the-sun-as-a-gravitational-lens-telescope-this-is-what-a-planet-at-proxima-centauri-would-look-like/ 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 2y ago
  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 2y ago
    Yeah, you basically need to launch a new one for every target you want to image.
    - Tomte 2y ago
      Probably even many, because it‘s energetically impractical to stop at the focal point.
      - skykooler 2y ago
        The neat thing about a how an Einstein ring works is that you don't need to stop, because rather than there being a focal point, there is a focal line, moving directly outward from the Sun. This means a probe could spend potentially decades imaging the same target on its outward path, if it had sufficient power.
    - Voultapher 2y ago
      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.
munchler 2y ago
> 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 2y ago
  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 2y ago
    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 https://arxiv.org/abs/2210.10833 [2]: https://arxiv.org/abs/2204.03020 https://arxiv.org/abs/2204.03020
- dleary 2y ago
  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-new-light-on-cosmic-reionization/ https://www.universetoday.com/168872/webb-observations-shed-...
waltbosz 2y ago
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 2y ago
  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 2y ago
    But wouldn't the size and age of the universe also imply that someone has looked at just the right moment somewhere somewhen.
    - drexlspivey 2y ago
      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 2y ago
        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 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-for-worlds-most-powerful-laser/ 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 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-message 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.
bparsons 2y ago
If the lens curved light back toward us, could we see earth several million years ago?
- wizzwizz4 2y ago
  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 2y ago
    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 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 https://en.wikipedia.org/wiki/Age_of_Earth : > 4.54 × 10^9 years ± 1% "J1721+8842: The first Einstein zig-zag lens" (2024) https://arxiv.org/abs/2411.04177v1 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-lens-is-a-cosmic-telescope-into-the-distant-universe-76798 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 https://youtube.com/watch?v=0jHsq36_NTU
lutusp 2y ago
> ... "in a way where" ... ... so that ... The elements of Style (https://en.wikipedia.org/wiki/The_Elements_of_Style https://en.wikipedia.org/wiki/The_Elements_of_Style) : "Make every word count." > ... "acts as a compound lens" ... Not really -- not the sort of lens we're familiar with, one that concentrates light at a single focus. Technical methods can exploit these chance alignments to detect objects otherwise inaccessible, but not as coherent images. I often see remarks like this one -- "Acts as a compound lens!" -- but that's not correct. It's more like this: https://arachnoid.com/relativity/graphics/curvature_diagram.png https://arachnoid.com/relativity/graphics/curvature_diagram.... Such alignments are more likely to produce what's called an "Einstein ring" (https://en.wikipedia.org/wiki/Einstein_ring https://en.wikipedia.org/wiki/Einstein_ring). Very useful, but not remotely a "compound lens". See Figure 7 in (https://arachnoid.com/relativity/index.html#General_Relativity https://arachnoid.com/relativity/index.html#General_Relativi...) for an interactive gravitational lens simulator.
tempodox 2y ago
In case anyone was wondering, like me, what the MJy unit in the lower diagram is: It's Mega-Jansky. Just funny that it's then being rescaled by 10^-9. Why didn't they use Milli-Jansky in the first place? https://en.wikipedia.org/wiki/Jansky https://en.wikipedia.org/wiki/Jansky
- schiffern 2y ago
  > It's Mega-Jansky... Why didn't they use Milli-Jansky *megajansky, millijansky "All prefix names are printed in lowercase letters, except at the beginning of a sentence. Unit names are normally printed in upright type and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter (even when the symbol for the unit begins with a capital letter), except at the beginning of a sentence or in capitalized material such as a title... When the name of a unit is combined with the name of a multiple or sub-multiple prefix, no space or hyphen is used between the prefix name and the unit name... Examples: pm (picometre), mmol (millimole), GΩ (gigaohm), THz (terahertz)" Source: https://www.bipm.org/en/publications/si-brochure https://www.bipm.org/en/publications/si-brochure However yes, you raise a good question. I was surprised to learn that astronomy and astrophysics prefer CGS, so by convention the diameter of the Sun is given in centimeters, and the mass of the Sun in grams! For janskys there's no excuse though.
deleted 2y ago
[deleted]
deleted 2y ago
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deskamess 2y ago
Complete newbie on the topic of GL but I find it very interesting. Q: We seem to want to use our sun for GL experiments. And that requires sending something out 500 AU out for focal length purposes. My question is somewhat theoretical so assume there are no alignment issues for the following thought. Are we not already at the "focal point/line" of some other 'entities' (sun/heavy body/galaxy/etc) gravitational lens? Hmm... is that what this paper is talking about - the fact that the GL observation was made from Earth on some infinite focal length. Listening to other YT videos on the topic seemed to imply the resolution would be much higher. Or is the resolution location/technology related?
veunes 2y ago
How interconnected everything is, even on a cosmic scale

271 points by wglb 2y ago

With all the galaxies out there, it seems likely that Earth should be in the focus of lots of systems of this kind. Hopefully in the future we'll be able to find and use these galactic telescopes!

wglb 2y ago

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 https://arxiv.org/abs/2411.04177

travisporter 2y ago
Cool! Was hoping to see a magnification amount like 100x etc
hinkley 2y ago
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 2y ago
  Surely any such eclipse lasts a long time. From the perspective of our lifetimes it is static.
  - hinkley 2y ago
    The farther away they are the slower they would scan the sky behind them or go out of conjunction. So I guess one of the objects would have to be something relatively close.
    - yreg 2y ago
      Are we not talking about galaxies? No galaxy is "close".
- ben_w 2y ago
  Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way. The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years. So, unless you're even more optimistic about life extension technology than I am, not in our lifetimes, no.
  - vlovich123 2y ago
    > It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way. Relative to us. For the light itself it takes no time.
    - ben_w 2y ago
      Our own frame of reference is the only one that matters, given the comment I'm replacing to.
- consp 2y ago
  Isn't the idea to use the sun as a lense already enough? The main problem being the focal point at 500+ au.

photonthug 2y ago

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 2y ago

Fund the SGL Telescope! https://www.universetoday.com/149214/if-we-used-the-sun-as-a-gravitational-lens-telescope-this-is-what-a-planet-at-proxima-centauri-would-look-like/ 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 2y ago
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 2y ago
  Yeah, you basically need to launch a new one for every target you want to image.
  - Tomte 2y ago
    Probably even many, because it‘s energetically impractical to stop at the focal point.
    - skykooler 2y ago
      The neat thing about a how an Einstein ring works is that you don't need to stop, because rather than there being a focal point, there is a focal line, moving directly outward from the Sun. This means a probe could spend potentially decades imaging the same target on its outward path, if it had sufficient power.
  - Voultapher 2y ago
    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.

munchler 2y ago

> 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 2y ago
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 2y ago
  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 https://arxiv.org/abs/2210.10833 [2]: https://arxiv.org/abs/2204.03020 https://arxiv.org/abs/2204.03020
dleary 2y ago
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-new-light-on-cosmic-reionization/ https://www.universetoday.com/168872/webb-observations-shed-...

waltbosz 2y ago

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 2y ago
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 2y ago
  But wouldn't the size and age of the universe also imply that someone has looked at just the right moment somewhere somewhen.
  - drexlspivey 2y ago
    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 2y ago
      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 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-for-worlds-most-powerful-laser/ 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 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-message 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.

bparsons 2y ago

If the lens curved light back toward us, could we see earth several million years ago?

wizzwizz4 2y ago
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 2y ago
  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 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 https://en.wikipedia.org/wiki/Age_of_Earth : > 4.54 × 10^9 years ± 1% "J1721+8842: The first Einstein zig-zag lens" (2024) https://arxiv.org/abs/2411.04177v1 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-lens-is-a-cosmic-telescope-into-the-distant-universe-76798 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 https://youtube.com/watch?v=0jHsq36_NTU

lutusp 2y ago

> ... "in a way where" ... ... so that ... The elements of Style (https://en.wikipedia.org/wiki/The_Elements_of_Style https://en.wikipedia.org/wiki/The_Elements_of_Style) : "Make every word count." > ... "acts as a compound lens" ... Not really -- not the sort of lens we're familiar with, one that concentrates light at a single focus. Technical methods can exploit these chance alignments to detect objects otherwise inaccessible, but not as coherent images. I often see remarks like this one -- "Acts as a compound lens!" -- but that's not correct. It's more like this: https://arachnoid.com/relativity/graphics/curvature_diagram.png https://arachnoid.com/relativity/graphics/curvature_diagram.... Such alignments are more likely to produce what's called an "Einstein ring" (https://en.wikipedia.org/wiki/Einstein_ring https://en.wikipedia.org/wiki/Einstein_ring). Very useful, but not remotely a "compound lens". See Figure 7 in (https://arachnoid.com/relativity/index.html#General_Relativity https://arachnoid.com/relativity/index.html#General_Relativi...) for an interactive gravitational lens simulator.

tempodox 2y ago

In case anyone was wondering, like me, what the MJy unit in the lower diagram is: It's Mega-Jansky. Just funny that it's then being rescaled by 10^-9. Why didn't they use Milli-Jansky in the first place? https://en.wikipedia.org/wiki/Jansky https://en.wikipedia.org/wiki/Jansky

schiffern 2y ago
> It's Mega-Jansky... Why didn't they use Milli-Jansky *megajansky, millijansky "All prefix names are printed in lowercase letters, except at the beginning of a sentence. Unit names are normally printed in upright type and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter (even when the symbol for the unit begins with a capital letter), except at the beginning of a sentence or in capitalized material such as a title... When the name of a unit is combined with the name of a multiple or sub-multiple prefix, no space or hyphen is used between the prefix name and the unit name... Examples: pm (picometre), mmol (millimole), GΩ (gigaohm), THz (terahertz)" Source: https://www.bipm.org/en/publications/si-brochure https://www.bipm.org/en/publications/si-brochure However yes, you raise a good question. I was surprised to learn that astronomy and astrophysics prefer CGS, so by convention the diameter of the Sun is given in centimeters, and the mass of the Sun in grams! For janskys there's no excuse though.

deleted 2y ago

[deleted]

deleted 2y ago

[deleted]

deskamess 2y ago

Complete newbie on the topic of GL but I find it very interesting. Q: We seem to want to use our sun for GL experiments. And that requires sending something out 500 AU out for focal length purposes. My question is somewhat theoretical so assume there are no alignment issues for the following thought. Are we not already at the "focal point/line" of some other 'entities' (sun/heavy body/galaxy/etc) gravitational lens? Hmm... is that what this paper is talking about - the fact that the GL observation was made from Earth on some infinite focal length. Listening to other YT videos on the topic seemed to imply the resolution would be much higher. Or is the resolution location/technology related?

veunes 2y ago

How interconnected everything is, even on a cosmic scale