Some fun stuff expected in 2016 in astrophysics...

[Anomalocaris]

Very coolomorphic. I wonder if one can see exoplanets from the shadows they cast in nebulae...

They won't cast much of a shadow if the star is much larger than the planet, just like low flying plane casts a shadow smaller than the plane, while a high flying plane casts no shadow at all on the ground.

[vorlon13]

BTW, contrails cast shadows, and they are totally fascinating.

[vorlon13]

[Alex K]

Very coolomorphic. I wonder if one can see exoplanets from the shadows they cast in nebulae...

They won't cast much of a shadow if the star is much larger than the planet, just like low flying plane casts a shadow smaller than the plane, while a high flying plane casts no shadow at all on the ground.

True... not a complete shadow anyway which will only extend a fraction of the distance star-planet, again only partial dimming, probably obscured by other effects...

[vorlon13]

A very large planet near a very small but very bright star would be a 'best case scenario' for seeing a shadow projected onto a conveniently nearby nebulosity.

Now, for the problems with that:

*very bright stars that are very small 'apparently' don't have planets

*very bright stars tend to be massive, regardless of physical size, so if there were a very large planet very close to one, it would have an enormous orbital velocity, and then unfortunately, the projected shadow is going to move very fast, our telescopes will need very large apertures to get exposure times fast enough at a high enough magnification that no one could afford to build such a telescope


So, the appropriate planets probably don't exist, and proving they do or don't is going to be very expensive.


Sorry . . .

[Anomalocaris]

A very large planet near a very small but very bright star would be a 'best case scenario' for seeing a shadow projected onto a conveniently nearby nebulosity.

Now, for the problems with that:

*very bright stars that are very small 'apparently' don't have planets

*very bright stars tend to be massive, regardless of physical size, so if there were a very large planet very close to one, it would have an enormous orbital velocity, and then unfortunately, the projected shadow is going to move very fast, our telescopes will need very large apertures to get exposure times fast enough at a high enough magnification that no one could afford to build such a telescope


So, the appropriate planets probably don't exist, and proving they do or don't is going to be very expensive.


Sorry . . .

Hmm, had an idea.

A planet in orbit around a neutron star?  The planet would be much bigger than the star, and if the planet is  close to the star compared to the nebulosity, it can cast a giant shadow, many times the planet's own size, on the nebulosity beyond.

There is at least one known family of exoplanets that orbit a neutron star.

[Alex K]

A white dwarf maybe?

[vorlon13]

The neutron star with the planets (3 as I recall) is believed to have formed it's planets during the supernova explosion that turned the prior form of the star inside out and left the compressed lump of neutrons behind.

Not quite a scenario that is going to make the system at Tabby's star.

White dwarfs are screaming bright for their size, but since they are so small, they aren't really that bright comparatively. The one at the Sirius system is extremely hot, but it isn't very bright, it contributes a tiny percentage of the total light there.

[Anomalocaris]

I wasn't think neutron star or white dwarf was an plausible explanation for tabby's star.  Just they create the environement that makes it plausible to study planets by the shadows they cast a third object.

In tabby's case, it appear all the solutions depend on some very large semi-cohesive body either casting shadows on other bodies, or blocking light directly.  This does not easily explain longer term dimming trend. The sun has a 11 year sunspot cycle.  I wonder if the solution to tabby could be some long lasting sunspot cycle lasting a few hundred years that involve enormous sunspots? Or some other intrinsic instability of the star?   Is there any Doppler evidence to show the star's surface is pulsating to an unusual degree?  Or there are large amount of material being shed from the star's surface?   Could this be a star caught in a the act of some short lived, and hence rare to observe, but highly variable phase?

[vorlon13]

as I recall it is an 'ordinary' F type star, save for the weirdness orbiting it

F stars are more massive, brighter, somewhat less common and shorter lived than our G type sun.