The Light bridge between LMC and Milky Way?

[timokarhula (Timo)]

I think this forum is perfect for my question. I'm an amateur astronomer from Sweden who regularly makes a trip to Western Australia, because I have an apartment in Geraldton after my late father. Last year, in November - December, I made a trip 130 kms to the inland where light pollution is unknown. My naked eye limiting magnitude was 7.9 and the SQM-L meters showed 22.09 magnitude per square arc-seconds! For the first time in 13 trips south of the equator, I observed a bridge of light between the LMC and our Milky Way. I have written a lengthy article of my astro-trip for the Deep-Sky Observer magazine of the Webb Society which will be published this winter or next spring. Here is an excerpt from my article:

"The light bridge of the Large Magellanic Cloud

The journey’s most exciting and unexpected sky phenomenon that we observed, was without a doubt, the light or materia bridge (as I call it) of the Large Magellanic Cloud, LMC. It is not even scientifically studied yet and only a handful of people have reported it in the literature! Lowell astronomer, Brian Skiff, confirmed my description of the ’thing’ and he had seen the bridge from Las Campanas observatory in Chile. US amateur, David Riddle, had noticed this bridge while being in Namibia. Apparently, the first who reported this light bridge in the astronomical literature was the Russian born astronomer Sirgay Gaposchkin in his article The Visual Milky Way in Vistas in Astronomy, vol. 3. He had sketched the object from Mt. Stromlo observatory while he scrutinized the southern Milky Way during the years 1956-57. Isn’t it strange that only northern observers have reported this phenomenon when they have visited the southern hemisphere?

With our unaided eyes, we noted how the light band reached from the LMC, went due south, passed the south celestial pole and continued along a great circle towards the Norma starcloud in the Milky Way. The materia bridge was nearly as wide as LMC itself and more than 40° long. In surface brightness it was comparable to the faintest part of the zodiacal band and maybe half of the gegenschein’s. In the beginning of the night, it reminded me of a waterfall that disappeared into the airglow near the horizon. Later in the night, this phenomenon had rotated clock-wise around the south celestial pole which proved that this was indeed an astronomical feature and followed the earth’s rotation. The materia bridge disappeared in Triangulum Australe, near its alpha star, Atria. It is most remarkable that nobody (as far as I know) has taken photographs of the light bridge! It is neither visible on Axel Mellinger’s panorama of the Milky Way which reaches the surface brightness level of about 24 magnitudes per square arc-second. This phenomenon shall not be confused with the Magellanic Stream which is only visible in radio wavelengths and goes in other direction. My theory is that our observed light bridge is the combined light from millions of faint stars or gas that Milky Way has ripped off from our satellite galaxy due to tidal effects at an earlier close passage. The light can also originate from intergalactic cirrus, like those clouds that can be seen near M81 in extremely deep photographical exposures. Spectroscopic analyses of the light should settle this matter. Curiously enough, the southern celestial pole is involved in a faint band of light while the northern pole, near Polaris, is the starting point of a dark lane in the Milky Way (have you seen it?)."

I suspect a sky capable of showing stars to magnitude 7.5 or has a darkness of about SQM 21.9 is necessary to show the light bridge between the LMC and the Norma Starcloud. Has anyone on this forum seen the bridge of light? It would be very strange if nothing more is known of this naked-eye feature!

Clear Skies!

Timo Karhula

[Ro84 (Roberto)]

Hello Timo Karhula

There is indeed a known stream of gas and faint stars between the Milky Way and the LMC, the so-called "Magellanic Stream", as you say, spanning from Carina to LMC, SMC and Pisces-Pegasus-Andromeda constellations (see http://apod.nasa.gov/apod/ap100125.html). Normally this gas can't be visible (it emits mostly radio-waves), as you say...

When I was near the equator I wasn't able to see any light connecting Milky Way and LMC, also under very dark sky... surely somebody here will have more and more experience of southern sky than me.

TrA-Aps have also their own nebular system, a sort of "Integrated Flux Nebula" similar to that of UMi-UMa in northern sky, belonging to our spiral arm, in the Milky Way Galaxy.

Some of the publications about the Magellanic Stream:
http://adsabs.harvard.edu/cgi-bin/np...pJ...173L.119W
http://adsabs.harvard.edu/cgi-bin/np...ASJ...32..581M
http://adsabs.harvard.edu/cgi-bin/np...NRAS.339.1135Y
http://adsabs.harvard.edu/cgi-bin/np...NRAS.363..509M

But this is the first time that I hear about this phenomenon.

[ngcles]

Hi Timo,

Welcome to our little southern hemisphere forum.

It is a coincidence you mention this as I spent a little time a couple of weeks ago searching for this bridge at Mudgee NSW on a night where the SQM-L reading at Zenith hovered around the 21.85-90 mark pretty much all night and peaked at 21.91 a little after midnight.

After reading your earlier accounts of it on the AMASTRO mailing list, I made a point of looking for it and came away disappointed to have not detected it.

Is the sketch by Gaponskin on-line somewhere so I can get a better appreciation of its appearance than words can convey?

Have been looking for it on and off for a few years now -- will continue to look -- good on you Timo and welcome!


Best,

Les D

[that_guy (Tony)]

:O i better check this out when im at a dark sight next!! It sounds awesome!! grab me self a lawn chair and lay back...

[timokarhula (Timo)]

Originally Posted by ngcles

Hi Timo,

Welcome to our little southern hemisphere forum.

It is a coincidence you mention this as I spent a little time a couple of weeks ago searching for this bridge at Mudgee NSW on a night where the SQM-L reading at Zenith hovered around the 21.85-90 mark pretty much all night and peaked at 21.91 a little after midnight.

After reading your earlier accounts of it on the AMASTRO mailing list, I made a point of looking for it and came away disappointed to have not detected it.

Is the sketch by Gaponskin on-line somewhere so I can get a better appreciation of its appearance than words can convey?

Have been looking for it on and off for a few years now -- will continue to look -- good on you Timo and welcome!


Best,

Les D

Hi Les,

Unfortunately, I haven't seen the sketches by Gaposhkin either! I only got this information from Dave Riddle in the thread a year ago in Amastro forum. I have never seen a sketch or a photo of the feature but the accounts of Skiff and Riddle exactly match mine.

It's very strange that this light has not been imaged. I hope someone takes the challenge and photographs this in a wide-field photo that frames the area between LMC and the Milky Way in Triangulum Australe / Norma. If the entire zodiacal band can be caught on a photo, then the LMC bridge should be caught as well.

I saw the LMC bridge also from a slightly inferior site with the sky darkness SQM-L 21.93 (ZLM 7.4+). It took me 13 trips south of the equator to see this elusive thing.

/Timo Karhula

[Waxing_Gibbous (Peter)]

Hello and welcome, Timo.
I too have looked for this and come home dissapointed. Mind you, it took me about twelve goes to find M1, so I'm not the best reference!
Thanks for posting the links and I shall persevere.
Peter

[CometGuy]

Hi Timo,

Interesting, I've wondered about observations of the bridge myself and I had a feeling that John Bortle had seen it. The lack of photographic observations is also interesting, maybe this could be a good project for somebody with a very dark sky.

Terry

[avandonk]

The best image I have was taken by Hiro. See IIS thread here

http://www.iceinspace.com.au/forum/s...t=62876&page=2

Here is the image 14MB

http://d1355990.i49.quadrahosting.co...6/Hiro_SCP.jpg

Here is a crop of the SMC and LMC 10MB

I made a crop version with just the green channel inverted 6MB

http://d1355990.i49.quadrahosting.co...1/greenBW1.jpg

This should better simulate what is seen visually.



These images were taken from very dark skies in WA but both Magellanic clouds were low in the sky.

Hope this helps a bit. Bert

[CometGuy]

Thx Bert had forgotten about those. The bridge should extend to upper left from the LMC in those images but can't convince myself of anything in those except for what looks like a dust cloud.

Bert have you done any gradient correction in those images that might mask any broad scale structures?

Terry

[timokarhula (Timo)]

Originally Posted by avandonk

I made a crop version with just the green channel inverted 6MB

http://d1355990.i49.quadrahosting.co...1/greenBW1.jpg

This should better simulate what is seen visually.

These images were taken from very dark skies in WA but both Magellanic clouds were low in the sky.

Hope this helps a bit. Bert

Great pictures! These images show the region between the Clouds and the Gum nebula in Vela. However the LMC light bridge goes to the upper left corner, towards Atria and beyond. However, some subtle brightening might be seen along this path towards the south celestial pole. An interesting faint patch of nebulosity is visible in the borderland of Chamaeleon-Octans-Mensa, about the size of SMC. The light bridge should be brightest in the Apus area (just beyond the upper left corner). The images should have twice the field of view.

Brian Skiff informed me on December 19, 2009, that he had once seen an image of the LMC bridge taken with a "parking lot" (?) fish-eye lens at Las Campanas, Chile.

"Greetings Timo. The bridge from the LMC toward the galactic center that you describe is just what I saw on both of my trips to Las Campanas in Chile. It basically extends straight south from the LMC to the south celestial pole, then follows a great-circle approximately to the Norma starcloud (or, alpha TrA, as you say) --- it runs into the Milky Way, so you lose it much like the zodiacal band close to the Milky Way. I, too, have wondered why it is not mentioned anywhere that I know of. I remember once seeing an image taken at CTIO using what they called the "parking lot camera", a wide-field lens + CCD. This image showed the feature, but I do not know where to find that image again.

I do know it is not the "Magellanic Stream" from the professional literature: this is a radio-wavelength feature (neutral hydrogen, CO and other gases) that goes in a different direction and reaches into the northern hemisphere.

The Axel Mellinger composite all-sky images should show it,but I think his calibration "flatted" it out of the final images.

\Brian"

/Timo Karhula

[timokarhula (Timo)]

Originally Posted by CometGuy

Hi Timo,

Interesting, I've wondered about observations of the bridge myself and I had a feeling that John Bortle had seen it. The lack of photographic observations is also interesting, maybe this could be a good project for somebody with a very dark sky.

Terry

Hi Terry,

Remember me in Roxby Downs exactly (!) 8 years ago? Well, I asked John Bortle today and he suggested me to ask talented southern astrophotographers to confirm the existence of the bridge. A good friend of mine, Christian Sasse in Canada, happens to be the co-owner of the Global Rent-a-scope system (GRAS) with high quality robotic telescopes in both New Mexico and South Australia. I could ask him to produce a gigantic deep CCD mosaic of the area between the galaxies. This will take some telescope time but it is certainly worth it if we get positive results.

/Timo Karhula

[CometGuy]

Hi Timo,

I certainly do remember you from Roxby Downs! It was sort of like a mini comet observers convention LOL

Terry

[timokarhula (Timo)]

Originally Posted by timokarhula

Brian Skiff informed me on December 19, 2009, that he had once seen an image of the LMC bridge taken with a "parking lot" (?) fish-eye lens at Las Campanas, Chile.

"Greetings Timo. The bridge from the LMC toward the galactic center that you describe is just what I saw on both of my trips to Las Campanas in Chile. It basically extends straight south from the LMC to the south celestial pole, then follows a great-circle approximately to the Norma starcloud (or, alpha TrA, as you say) --- it runs into the Milky Way, so you lose it much like the zodiacal band close to the Milky Way. I, too, have wondered why it is not mentioned anywhere that I know of. I remember once seeing an image taken at CTIO using what they called the "parking lot camera", a wide-field lens + CCD. This image showed the feature, but I do not know where to find that image again.

Hi all!

Guess my surprise when I recently also saw a glimpse of the LMC "light bridge" on TV! It was in a nature program from the Atacama desert. On a time-elapse sequence showing the Chilean observatories in the foreground, the Magellanic Clouds were revolving around the south celestial pole (SCP). From the LMC, I could faintly see the "light bridge" going towards the Milky Way in Triangulum Australe / Norma. This was apparently shot with a b/w CCD-camera and a very wide field or a fish-eye lens. I think this is the best equipment to catch the elusive "light bridge". Could anyone Down-Under with very dark skies try to image the LMC / SCP with a CCD + fish-eye lens? You who succeed will be (one of) the first to prove the existence of the LMC bridge!

Clear Skies,

Timo Karhula

[timokarhula (Timo)]

Brian Skiff of Lowell Observatory gives here some further advice how to image the LMC Light Bridge.

"A couple of points to mention in regard to picking it up
both visually and photographically. The best time for viewing is
at around sidereal time 12h, when the LMC is over in the west and
the galactic center is rising in the east. Look along the line
between the two, which goes beneath the Milky Way.
For imagers:

1) It is worth emphasizing that the feature is very large,
and of low (but not especially low) surface brightness,
about like that of the zodiacal band on either side of the
Gegenschein. Thus the camera lens should be stopped down to
avoid vignetting.

2) In addition, imagers are fond of processing their results
to "flatten out" such large scale features --- obviously you will
miss it if you apply any cosmetic processing of this sort:
turn off that button in your software!

3) Another point is to use a filter or do whatever is necessary
to avoid picking up the night-airglow pattern; if the detector is
sensitive in the far-red, this could swamp the "light bridge".
The goal would be to record only in the visual (or blue-green-yellow)
range of wavelengths, _excluding_ H-alpha and redder."

/Timo Karhula