A giant cat ate something really big?
Science sure is hard...
Tabby's star – formally KIC 8462852 – has attracted a new and possibly-plausible explanation for its excess of twinkle: the remnants of a planet destroyed in a collision. That hypothesis comes from Brian Metzger and Nicholas Stone of Columbia University's Astrophysics Laboratory, and Ken Shen of UC Berkeley's Department of …
Whereas all space programs (on TV) show that if planet Earth was swallowed up by our Sun (when it expands as it dies), it just gets absorbed into the Sun, not shattered into a million pieces. Probably because the Earth is made of rock and the Sun is just a bit of gas. Can't see why Tabby's star would be any different.
Gravitational stress as the planet neared the star can be sufficient to cause break up; the boundary at which this starts to occur being the Roche Limit. As the planet nears the star the gravitational stress caused by the star overcomes the forces holding the planet together and so it starts to disintegrate, with the planetary remnants being pulled into a nice twinkle-causing spiral of debris around the star.
Mars's moon, Phobos, is thought to be currently undergoing this unfortunate demise.
not sure what the gradient would need to be.
obviously planets in original orbits arent going to spontaneously fall apart - they wouldnt have formed in the first place if there wasnt some kind of stability and attraction..
any force sufficient to push a planet out of a stable orbit into something that approachs its primary close enough to pull it to bits - is probably enough to shatter said planet anyway.
Stellar expansion due to aging wouldnt do it - no change to the masses involved. Besides, I have a vague memory of the article i read 5 minutes ago mentioning it being an F type star, which I believe is similar to our G type ... who doesnt remember WOBAFGKMRNS as the catchy sequence of star types, doesnt even need a mnemnomic.
"any force sufficient to push a planet out of a stable orbit into something that approachs its primary close enough to pull it to bits - is probably enough to shatter said planet anyway."
There's a M dwarf companion which could disrupt planetary orbits and send them on a slow inspiral.
Stellar expansion due to aging wouldnt do it - no change to the masses involved.
Right up until the star expanded enough the planet's orbit was inside the star's atmosphere, or soon before. While the mass wouldn't change, the fact that the planet was going through a cloud of hot gas would cause its orbit to deteriorate. Prior to that, the planet would be affected by heating which may cause loss of mass when combined with the solar wind more than previous in the life of the stellar system.
@YAOFM - you've actually answered your own question in your parenthesis "(when it expands as it dies)".
Any body with non-zero mass distorts the nominally flat space-time around it (in theory, to infinity) producing the effect of Gravity. The degree of distortion is at its greatest at the surface of the body and decreases with distance from it in accordance with the inverse square law principal, creating a gravitational gradient, the steepness of which decreases with distance from the originating body.
The upshot of this is that any body within a gravitational gradient will have a greater gravitational force acting on one side of it and a lesser gravitational force acting on the other side of it, creating an internal tension within it due to the imbalance of the forces and with the degree of imbalance, and therefore the internal tension, being relative to the steepness of the gradient; a steep enough gradient will pull anything apart.
However, the steepness of the gradient is not only dependent upon the mass of the body but also its size; for two equal masses, a smaller, more dense body means that you can get closer to all of its mass than you can for a larger, less dense body. For example, if we take two bodies that have the same mass but one body is 1unit size in diameter and the other body is 2 units size in diameter it means that we can get to within 1 unit distance of all of the mass in the smaller body but can only get to within 2 units distance of all the mass of larger sized body. Thus, we can be in a steeper gravitational gradient with the smaller body than we can with the larger body, even though they have the same mass.
Now when a star expands, as it starts its departure from the main sequence, it doesn't increase in mass (it'll actually be losing mass) so as it increases in size its density will drop and the maximum steepness of the gravitational gradient it can produce will decline; by the time that Sol expands to the size of Earth's orbit the steepness of its gravitational gradient in the vicinity of Earth will actually be a bit lower than it is now and, so Earth won't be pulled apart.
Actually, I believe those TV shows are correct. The fact that the Sun will blow up to a gas giant the size of Earth's orbit will not influence the Roche limit of the Earth with respect to the Sun.
Formula I got from Wikipedia:
d = 1.26 R_m ( M_M / M_m)^(1/3)
d = Roche limit
R_m = radius secondary (Earth)
M_M = mass primary (Sun)
M_m = mass secondary (Earth)
Neither R_m nor M_m is going to change materially, M_M is only to get less due to the Sun shedding gas.
So d will not be larger than today, Earth will not be pulled apart but dive into the Sun in one piece. What a relief.
It's a shame that not all people read all posts, or you'd see that I'm not a random poster.
http://m.forums.theregister.co.uk/forum/1/2016/10/14/apples_macos_sierra_update/ (edited for this repost):
"Its" is the possessive: "its light isn't stable".
"It's" is *always, without exception* an abbreviation of "It is" or "It has". Never anything else.
"it is light isn't stable" and "it has light isn't stable" makes no sense.
It's not hard, for God's sake...
* "Illiterate? Don't know the meaning of the word..."
Language matters. If a professional writer is incapable of getting it right, and the editors are incapable of picking it up (since to me it jumps off the page as egregiously wrong) then they should improve their education or change their jobs.
I just had to check where the name Tabby's Star had come from. Turns out it's named after the astronomer who led the study that revealed the star's odd behaviour.
So good news for Tabby: She has a star named after her, which is definitely worthy of some kudos (a real star with a real name, not a worthless piece of paper from the Institute of Stellar Naming). Even better news for her, her star is an "interesting" one scientifically.
But bad news for her if this latest report is accurate because it seems like her star is busy gobbling up its planets, which means it's less likely to have aliens, and less likely to be worth visiting when we do finally invent the technology to do so. Oh well, never mind, eh?
Part of the issue here is that all TV/Movie/SF entertainment show this process happening over *minutes* at best. Nature is *not* McDonalds. Your natural phenomena tend to take a *heck* of a lot longer to occur at solar scale. I'll grant you that once things start scaling down a good bit, things can happen faster. (quasars etc).
@eldaka - nice theory, except building a Death Star would probably actually be cheaper!
On the subject of why planets would change their orbits and whether or not they'd get ripped apart, two things to note; first, that stars are dynamic things, that change over time, and second - so are plentary systems. I fyou think the planets in our solar system have always been exactly where they are right now and always will be, even without passing stars causing disruption, then , sorry, but you're wrong. All kinds of interesting resonance effects can, over very long periods of time, cause orbits in planetary systems to change, sometimes only in minor ways very occasionally dramatically. But given the universe has thousands of millions of years to play with, eventually those low-probability events occur, or teh cumulative effects of minor perturbations grow into major perturbations.
In short, Tabby's Star wouldn't necessarily have had to expand in order for it to be snacking on its planetary system (although as a poster above rightly pointed out, if a star does enter red giant phase, any planet that gets caught in the outer fringes of its atmosphere will eventually spiral inwards due to drag).
As for whether a planet would be torn apart, it'd first suffer loss of volatiles due to heating, effectively turning teh doomed planet into a super-sized comet (and the volatiles would freeze once sufficiently far from the star, and possibly start clumping together again - over time). Then what was left would start melting, and some stuff that we don't normally consider volatile might start boiling off.
The cohesiveness of the body being eaten comes into play - an asteroidal rockpile takes less to be torn apart than something more solid, but when thinking about a plnet like , say Earth, don't forget that Earth isn't for the most part solid - the bulk of it is, in fact, a very hot dense liquid under immense pressure, overlain by a few kilometres of crust. Or to put it another way, we're not living on Granny's rock cakes writ large - more like the skin on her rice puddings. Anything that relieves the pressure on the interior of the planet would cause such interesting things to happen that you could make several fortunes selling tickets to watch to scientists and astro-geeks like me. Even better if it's something Jovian being eaten. We'd just LOVE to get a look at the interior of a Jovian.. - from a suitably safe distance, of course!..
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