Slashdot posting, 1950 astronomical transient

"Exploring nine simultaneously occurring transients on April 12th 1950"

A new (potential) Slashdot submission. This is my working copy.

Working Title : Did you see that?

Paper : https://arxiv.org/pdf/2106.11780.pdf

9 authors, including one un-person (Geoff Marcy) from 10 institutions from the USA, via Spain (Gran Canaria), Sweden and the Ukraine, and ending up in India. In other words, the usual international football team.

A paper just published on Arxiv, the astronomy/ physics/ computing/ mathematics preprint service, describes studies into old astronomical data sets, to prepare the ground for the "transient" phenomena which will be discovered by new "repeated survey" telescopes. These will photograph the whole sky every few days, capturing novae and supernovae, many new Solar system bodies, the new "mega-constellations" of thousands of satellites, and other, more surprising "transient" phenomena.

In the early 1950s the then-new "200 inch" Hale telescope at Mt Palomar was employed in performing a sky survey. They would take a plate (literally, a glass plate ; this was long before electronic image capture) with a blue-sensitive emulsion, then a plate with a red-sensitive emulsion ; six days later, another red plate covered the same area (by planned overlap). The middle red plate showed a cluster of 9 objects, covering about a tenth of the full Moon's apparent size, which weren't visible in the previous blue plate, nor in the subsequent red plate. The simplest astronomical explanation is that 9 objects of red colour appeared and disappeared in that time interval.

As astronomers get more short-interval surveying of the sky, they get a better idea of how often such "transients" occur. Individual transients (novae, unidentified Solar system bodies, etc) are not, themselves, rare. But nine, in such a small area, in such a short time period - that is rare.

A sceptic's first question would be - is the data good? Photographic plates are a mature technology - and were around a century old at the time of taking. Nobody knows of a similar "contamination" process. Millions of plates have been scanned into computers after the glassware was replaced with CCD detectors - again, nobody has found a similar set of contamination marks. Ideas such as grains of dust from the Alamagordo atomic tests getting onto the plates (and being washed off in the processing) were considered, but it is very unlikely that no other plates for the same manufacturer show similar defects. Human events (matches producing "flares" in spectroscopic observations ; the infamous "Fast Radio Burst" microwave oven) were considered, such as an astronomer with hayfever spraying the plate with snot droplets. But again, why haven't comparable artefacts been found on other plates - and people have looked, digitally, for them! Water drops and processing chemical streaks have characteristic sizes, which these images don't. 

A fragmenting asteroid ("small body") was considered. But that would leave images substantially elongated by the Earth's motion - and only one of the 9 "transients" showed signs of elongation. Some astronomers used to refer to asteroids as "the vermin of the skies" referring to their common occurrence on the sky - invariably through the middle of what you were really trying to photograph. The term is being re-purposed for satellite megaconstellations.

What about a meteor fragmenting in the atmosphere above the telescope? They take too long, and produce even longer streaks than asteroids. They are photographed often enough to be well understood, and this image isn't one of those.

A satellite might produce a short enough "glint" of reflected sunlight. But ... the first satellite was launched 7 years after this image. Unless the launch records from Area 51 say differently.

One event, with 8 reflections from some nearby objects, could work. But with the plate exposure being 50 minutes, the maximum spacing of the reflecting objects is about 30 light minutes, and the size of the spread means the object is about 0.02 light years away. Comfortably beyond the Voyager probes, launched over 20 years later. Unless the launch records from Area 51 say differently.

 

The obvious next step is to look at existing images of the area taken with newer technology. That has been done. The Pan-STARRS survey (2010 to "continuing" ; to 3.4 magnitudes dimmer than the plates managed - a factor of about 23-fold in brightness) saw nothing there. The Sloan Digital Sky Survey (SDSS, 2000 to "continuing"), to 16-fold dimmer than the plates, saw nothing there.  

To mis-quote Capt.Brody [no, Quint!], "We're gonna need a bigger telescope!" And that is what this report is about. Using the GTC (Gran Telescopio Canaria, 10.4m, ~409in) they photographed the region to a brightness (dimness) of 250-fold compared to the original plates. And they found a number of matches. That's not unexpected : the astronomers estimate the odds of getting such matches by chance as about 17% - far from impossible, but not terribly likely. 

Still, nobody knows what there objects were (or even if the 1950 observation was real)

 (The authors also consider the possibility that in the 70 years between observations, the original objects have drifted out of the field of study - in itself, that would mark them as likely outer Kuiper Belt objects, or Oort Cloud objects. In which case, the question of the simultaneous movement of 9 close objects remains a question. Cue the "I'm not saying it was aliens, but ..." video clip.)

 

This is a first draft. I'll post it to Slashdot after editing it down a bit.