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View Full Version : Do Comets Explain Mystery Starís Bizarre Behavior?



Fraser
2015-Nov-25, 03:11 PM
The story of KIC 8462852 appears far from over. You’ll recall*NASA’s Kepler mission had monitored the star for four years, observing two unusual incidents, in 2011 and 2013, when its*light dimmed in dramatic, never-before-seen ways. Models to explain its erratic behavior were so lacking that some considered the possibility that alien megastructures built to capture […]

More... (http://www.universetoday.com/123592/do-comets-explain-mystery-stars-bizarre-behavior/)

Ross 54
2015-Nov-25, 06:28 PM
A puzzling new cometary scenario for Tabby's Star dimming. The larger of the two major comet fragments is described as leading the procession, yet if I correctly understand the graphs presented, the largest dimming, by 22 percent, occurred after the smaller, 15 percent one, on days 1500 and 800 of the observations, respectively.
Even if we want to assume that the smaller comet fragment leads the larger, one wonders how they came to be separated to such an extent that one crossed the star's face 700 days after the other, with comparatively little debris seen between the two.
In any case mustn't we assume extraordinarily large, dense comet fragments to block 15 and 22 percent of the star's light? One reads that comets in our own solar system, crossing in front of the Sun, produce barely any dimming at all.
Perhaps the reason the Spitzer Space Telescope confirmed the absence of substantial dust in the Tabby's Star system is that there was and is none. If so, the dimming would presumably have to be ascribed to much larger objects, conceivably artificial ones.

DaveC426913
2015-Nov-25, 07:43 PM
A puzzling new cometary scenario for Tabby's Star dimming. The larger of the two major comet fragments is described as leading the procession, yet if I correctly understand the graphs presented, the largest dimming, by 22 percent, occurred after the smaller, 15 percent one, on days 1500 and 800 of the observations, respectively.

Huh. You're right. I wonder how they rationalize that.

DaveC426913
2015-Nov-25, 07:46 PM
Perhaps the reason the Spitzer Space Telescope confirmed the absence of substantial dust in the Tabby's Star system is that there was and is none. If so, the dimming would presumably have to be ascribed to much larger objects, conceivably artificial ones.
Something we have not seen before (such as a large comet, or large, dense dust cloud - implausible as they might be) is still many orders of magnitude more plausible than an artificial explanation. Let's not go down that rabbit hole till there's good reason to.

Ross 54
2015-Nov-25, 08:40 PM
Just wondering-- how do we know that an extraordinarily large comet, capable of streaming out an unprecedentedly dense cloud of dust, is more probable than an artificial explanation? We don't seem to have any information about the number of advanced stellar civilizations in out galaxy. If these are plentiful, wouldn't that have a lot of bearing on the probabilities involved?

DaveC426913
2015-Nov-26, 02:33 PM
Just wondering-- how do we know that an extraordinarily large comet, capable of streaming out an unprecedentedly dense cloud of dust, is more probable than an artificial explanation? We don't seem to have any information about the number of advanced stellar civilizations in out galaxy. If these are plentiful, wouldn't that have a lot of bearing on the probabilities involved?
Because
1] there is a huge precedent for comets. They are common as dandelions. There' s even a precedent for comets with halos as large as the sun (Holmes, 2007).
2] there is zero precedent for extraterrestrial civilizations with star-enveloping structures. Nor is there any precedent for any of the precursor condition upon which this one is dependent.

The single step to get from
what we have seen (giant cometary halos)
to what is required (giant, dense cometary halos),
is many, many orders of magnitude shorter a leap than the many, many steps from
what we have seen (nothing)
to what is required (habitable exoplanet > habitable exoplanet that harbors life > habitable exoplanet that harbors intelligent life > habitable exoplanet that harbors intelligent starfaring life > habitable exoplanet that harbors intelligent starfaring life with world-building technology > habitable exoplanet that harbors intelligent starfaring life with world-building technology and builds a structure whose size is on the order of magnitude of a star).

If any one of those (huge, huge) steps is not found, the whole chain is fantasy. For example, we have yet to spy a single habitable exoplanet. Therefore all that follows is fantasy.

citpeks
2015-Nov-26, 04:27 PM
As I was driving from Baltimore to Washington yesterday at sunset, I saw the condensation trails of five airplanes close to each other. The sky was blue and the air was dry, so that the trails looked like the tails of comets. I wish I could have stopped to photograph the image because it genuinely looked like the Earth was being bombarded by a cluster of comets.

The sky over Washington, D.C. is so crowded with airplanes that at any time between 7 PM and 11 PM there are at least five airplanes in any direction that I look. Only the brightest stars can be seen.

Ross 54
2015-Nov-26, 06:40 PM
Because
1] there is a huge precedent for comets. They are common as dandelions. There' s even a precedent for comets with halos as large as the sun (Holmes, 2007).
2] there is zero precedent for extraterrestrial civilizations with star-enveloping structures. Nor is there any precedent for any of the precursor condition upon which this one is dependent.

The single step to get from
what we have seen (giant cometary halos)
to what is required (giant, dense cometary halos),
is many, many orders of magnitude shorter a leap than the many, many steps from
what we have seen (nothing)
to what is required (habitable exoplanet > habitable exoplanet that harbors life > habitable exoplanet that harbors intelligent life > habitable exoplanet that harbors intelligent starfaring life > habitable exoplanet that harbors intelligent starfaring life with world-building technology > habitable exoplanet that harbors intelligent starfaring life with world-building technology and builds a structure whose size is on the order of magnitude of a star).

If any one of those (huge, huge) steps is not found, the whole chain is fantasy. For example, we have yet to spy a single habitable exoplanet. Therefore all that follows is fantasy.

It seems natural that there would be many more precedents based on comets, than on civilizations. It appears reasonable that the former are much more plentiful than the latter. As for civilizations, we have our own as precedent. We also have a couple of oft-heard scientific observations: 1.) That there are very probably other civilizations in space. and 2.) That nothing prevents us from eventually building megastructures in space, given the continued growth of our scientific and technical acumen.

It appears that the cometary scenario in the dimming of 'Tabby's Star' has its own set of problems:

*Could comets crowd in on a star, to the extent of dimming it by up to 22 percent, and leave behind no substantial and still-detectable dust?

*Comets releasing extraordinary amounts of dust would need to have comparable stores of such material within them. This seems to indicate that they could be much larger than the comets with which we are familiar. Wouldn't the gravity of these much larger bodies tend to retain their dust, rather than allow it to readily fly off into space?

* The proportion of dust and other opaque materials in comets with which we are familiar appears to be something on the order of one half of their total materials. Such comets, when they pass in front of the Sun scarcely cause any dimming at all. If we were to posit exo-comets with a higher proportion of dust than this, even doubling it to nearly 100 percent, we would still, it seems, fall far short of what is needed to dim a star by 22 percent.

DaveC426913
2015-Nov-27, 02:27 AM
A puzzling new cometary scenario for Tabby's Star dimming. The larger of the two major comet fragments is described as leading the procession, yet if I correctly understand the graphs presented, the largest dimming, by 22 percent, occurred after the smaller, 15 percent one, on days 1500 and 800 of the observations, respectively.
Even if we want to assume that the smaller comet fragment leads the larger, one wonders how they came to be separated to such an extent that one crossed the star's face 700 days after the other, with comparatively little debris seen between the two.

OK. I see. The reason they think the largest fragment is leading the others is because the 2011 dimming presents a very clean, smooth curve, as would be created by a single, large object. The second dimming event is chaotic, suggesting multiple objects in simultaneous transits. There's no reason why multiple medium-sized objects wouldn't block more light than a single large object.

DaveC426913
2015-Nov-27, 02:33 AM
It seems natural that there would be many more precedents based on comets, than on civilizations. It appears reasonable that the former are much more plentiful than the latter. As for civilizations, we have our own as precedent. We also have a couple of oft-heard scientific observations: 1.) That there are very probably other civilizations in space. and 2.) That nothing prevents us from eventually building megastructures in space, given the continued growth of our scientific and technical acumen.

It appears that the cometary scenario in the dimming of 'Tabby's Star' has its own set of problems:

*Could comets crowd in on a star, to the extent of dimming it by up to 22 percent, and leave behind no substantial and still-detectable dust?

Dust is normally detected by an IR signature. Cometary dust is put forth because it will tend to be cold, and spends most of its time in the cold distance. This is unlike an asteroid belt.



*Comets releasing extraordinary amounts of dust would need to have comparable stores of such material within them. This seems to indicate that they could be much larger than the comets with which we are familiar. Wouldn't the gravity of these much larger bodies tend to retain their dust, rather than allow it to readily fly off into space?

Until someone crunches those numbers, we can only speculate how much comet is enough.



* The proportion of dust and other opaque materials in comets with which we are familiar appears to be something on the order of one half of their total materials. Such comets, when they pass in front of the Sun scarcely cause any dimming at all. If we were to posit exo-comets with a higher proportion of dust than this, even doubling it to nearly 100 percent, we would still, it seems, fall far short of what is needed to dim a star by 22 percent.

We are also not familiar with what comets do around - and how many get sent sunward by - a companion star, such that sported by Tabby's Star. Sol is a good starting point as a precedent, but we should be careful how much we use it as a model.

This, counter-intuitively, increases the plausibility of a comet swarm as the culprit, since the companion star represents a "known unknown", indicating we should expect the unexpected.