# So where's this extra-galactic light coming from? **URL:** \ **Category:** Factual Questions\ **Created:** [December 12, 2020, 8:02pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920 "2020-12-12T20:02:16Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 12, 2020, 8:02pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/1 "2020-12-12T20:02:16Z")
Interesting study coming out. Data from New Horizon probe discovers more extra-galactic light than there should be. > **[Pluto probe finds mysterious night light in the universe | CBC Radio](https://www.cbc.ca/radio/quirks/dec-5-a-mysterious-light-from-the-universe-undoing-cellular-ageing-feather-talking-and-more-1.5827266/pluto-probe-finds-mysterious-night-light-in-the-universe-1.5827278)** > > NASA’s New Horizons spacecraft has detected light with no obvious source coming from beyond our galaxy. > **[Scientists Discover Outer Space Isn't Pitch-Black After All](https://www.npr.org/2020/11/18/936219170/scientists-discover-outer-space-isnt-pitch-black-after-all#:~:text=Space%20Is%20Dark%2C%20But%20Scientists%20Have%20Found%20Unexplained%20Light%20%3A%20NPR&text=Space%20Is%20Dark%2C%20But%20Scientists%20Have%20Found%20Unexplained%20Light%20Scientists,such%20as%20stars%20or%20galaxies)** > > Scientists have used a NASA probe way out in space, beyond Pluto, to measure visible light that's not connected to any known source such as stars or galaxies. > [@](#): > > Then they processed these images to remove all known sources of visible light. Once they’d subtracted out the light from stars, plus scattered light from the Milky Way and any stray light that might be a result of camera quirks, they were left with light coming in from beyond our own galaxy. > > They then went a step further still, subtracting out light that they could attribute to all the galaxies thought to be out there. And it turns out, once that was done, there was still plenty of unexplained light. > > In fact, the amount of light coming from mysterious sources was about equal to all the light coming in from the known galaxies, says [Marc Postman](https://www.stsci.edu/~postman/), an astronomer with the Space Telescope Science Institute in Baltimore. So maybe there are unrecognized galaxies out there, he says, “or some other source of light that we don’t yet know what it is.” > … > "It’s very difficult to turn around and say to the astronomical community, like, ‘Hey, guys, we’re missing half of the stuff out there,’ " Zemcov says. Still, he buys the results: “I think the work is really solid.” Space aliens with great big light generating bug eyes? Dark matter? God forgot to turn off his reading light? ---
**Author:** ![scarbrow](https://avatars.discourse-cdn.com/v4/letter/s/6a8cbe/32.png) [@scarbrow](https://boards.straightdope.com/u/scarbrow)\ **Post date:** [December 12, 2020, 11:28pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/2 "2020-12-12T23:28:20Z")
It would be pretty cool if this turns out to be the clue that helps us find dark matter. Seems to me more likely to be new dust clouds somewhere. Or a measurement error that is hard to detect. The real question is going to be if this can be seen from earth orbit or not. If someone finds a way, we have a chance to figure it out. If interference from being in the solar system makes it too hard to detect, it’ll be really tough to find the source. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 12, 2020, 11:28pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/3 "2020-12-12T23:28:36Z")
Did the subtract out specific known galaxies, or the amount of light expected from the known concentration of galaxies? Look at the [Ultra Deep Field](https://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field#/media/File:Hubble_ultra_deep_field_high_rez_edit1.jpg): That’s probably what the sky looks like all over. ---
**Author:** ![scarbrow](https://avatars.discourse-cdn.com/v4/letter/s/6a8cbe/32.png) [@scarbrow](https://boards.straightdope.com/u/scarbrow)\ **Post date:** [December 12, 2020, 11:46pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/4 "2020-12-12T23:46:51Z")
I have another idea after reading more. Apparently the New Horizon probe is just outside the Kuiper belt, which means it’s still well inside the Oort cloud, where comets come from. It seem possible to me that the Oort cloud has more comets than expected that are individually too small to be seen by the Hubble, but collectively add up to a diffuse light. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [December 13, 2020, 12:34am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/5 "2020-12-13T00:34:21Z")
What was the name of that paradox that says the night sky should be as bright as daytime, from all of the stars that have been shining for endless eons? It was used to help disprove the Steady State theory. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 13, 2020, 12:39am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/6 "2020-12-13T00:39:07Z")
> **[Olbers' paradox](https://en.wikipedia.org/wiki/Olbers%27_paradox)** > > Pages for logged out editors learn more > > > Olbers's paradox, also known as the dark night sky paradox, is an argument in astrophysics and physical cosmology that says that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. In the hypothetical case that the universe is static, homogeneous at a large scale, and populated by an infinite number of stars, any line of sight from Earth must end at the surface of a star and hence the night s... ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [December 13, 2020, 2:27am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/7 "2020-12-13T02:27:47Z")
Pertinent quote from the CBC article: > The team combed through the archive of images from the New Horizons mission and subtracted all of the known light sources, including stars in the Milky Way and distant galaxies. > > They also had to eliminate light that might be coming from the spacecraft itself, possible defects in the camera and possible errors in their calculations. So this is an inference made involving a number of factors that are all subject to error, not a conclusive direct observation. It’s possible that this is an interesting discovery having any of the causes that are being speculated, maybe even one of the exotic ones like dark matter interactions, but it’s also possible that it’s just an artifact. It’s also possible that the phenomenon is real but with a mundane explanation, like sources within the Oort cloud. I’m reminded of the incident back in 2011 when a neutrino beam at CERN was apparently traveling faster than light. In that case few seriously believed it, but neither could anyone explain the observation. It eventually turned out that there were, not one, but two, sources of error. When the errors were eliminated the anomaly disappeared. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 13, 2020, 2:34am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/8 "2020-12-13T02:34:46Z")
It would be neat if it were because the universe has closed topology, and is small enough that light is traversing the entire universe and coming back again. But I suspect that they have ruled that out, and in any case I guess light that came back around that way would still be seen as coming from a known light source. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [December 13, 2020, 2:36am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/9 "2020-12-13T02:36:25Z")
I wonder if gravitational lensing could be the culprit. Including microlensing, there may be a lot of magnifying of light from very distant galaxies. There are trillions of rogue planets and brown dwarfs out there, and they could be magnifying more distant light, making it have more impact than non-lensing models might assume. Just a guess, though. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 13, 2020, 3:52am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/10 "2020-12-13T03:52:38Z")
Nice hypothesis, Riemann. However, what with the 4 degree background radiation showing us a finite distance limit to the observable universe, I think we have something different here. Maybe dark matter has a slight interaction cross section with intergalactic hydrogen? ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [December 13, 2020, 5:13am UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/11 "2020-12-13T05:13:05Z")
Oops! I think I left the fridge door ajar. Hang on, gimme a sec… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 13, 2020, 2:08pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/12 "2020-12-13T14:08:18Z")
In terms of the amount of excess light, a topologically nontrivial universe would look the same as a topologically trivial one. Where in the one you’d get light from the same sources “wrapping around”, in the other you’d get light from sources that are just plain more distant. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [December 13, 2020, 2:36pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/13 "2020-12-13T14:36:27Z")
> [@Elendil\_s\_Heir](#): > > Oops! I think I left the fridge door ajar. Hang on, gimme a sec… Was that meant for a Thread Games thread? ---
**Author:** ![JohnT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnt/32/15048_2.png) [@JohnT](https://boards.straightdope.com/u/JohnT)\ **Post date:** [December 13, 2020, 3:02pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/14 "2020-12-13T15:02:25Z")
> [@Squink](#): > > Nice hypothesis, Riemann. ISWYDT ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [December 13, 2020, 3:24pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/15 "2020-12-13T15:24:43Z")
Of course I’d love it if this pointed the way to dark matter, or even some other phenomenon, but it’s more likely to be something boring, given: 1. The estimate for number of galaxies in the observable universe was recently about doubled (IIRC) based on the most complete survey. 2. The amount of material in the filaments between galaxies was recently revised up. So either of these could be the explanation depending on what the dataset was for this research. Also there’s a third factor: 1. The universe hates us ---
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [December 13, 2020, 4:27pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/16 "2020-12-13T16:27:37Z")
Backscatter. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [December 13, 2020, 4:44pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/17 "2020-12-13T16:44:06Z")
So with the tendency to name any unexpected phenomena showing up in cosmology ‘dark’ something—dark matter, dark energy, dark flow, dark fluid—is this going to get called ‘dark light’? ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [December 13, 2020, 4:44pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/18 "2020-12-13T16:44:31Z")
> [@Sam\_Stone](#): > > I wonder if gravitational lensing could be the culprit. A lens cannot magnify light; it only concentrates it. There has to be a source of energy unaccounted for. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 13, 2020, 9:15pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/19 "2020-12-13T21:15:20Z")
I don’t understand how there can be light with an unknown source. Light generally travels in straight lines - you can literally use it to capture an image of the source. Sure, the image may be faint or indistinct or fuzzy or distorted, or some such, but it’s _light_, not a fart inside an elevator. It’s coming from _somewhere_ by definition of what it is. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 13, 2020, 9:18pm UTC](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920/20 "2020-12-13T21:18:08Z")
Mangetout, Space mighty be foggy enough to diffuse distant light sources beyond recognition. [Next page](https://boards.straightdope.com/t/so-wheres-this-extra-galactic-light-coming-from/927920.md?page=2)