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The Astronomy Thread 
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Post Re: The Astronomy Thread
That's what happens when objects get very dense; you can get very close to a large mass. The tides would probably be pretty hellacious, too.

Low-mass stars have a strange property where the puffy gas envelope of a huge gas giant crosses some tipping point and becomes compressed. Which is counter-intuitive, since you would think the new outward pressure from the fusion reactions would increase the diameter rather than shrinking it. Or maybe it's because the puffy outer layers get blown off as the process begins. But it's almost all hydrogen anyway, so I'm not sure that makes sense either.

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Thu Jul 13, 2017 11:00 am
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Post Re: The Astronomy Thread
The universe isn't here to satisfy human sensibilities, so some counter-intuitiveness should be expected, and treated as suspect when it isn't found. ;)

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Thu Jul 13, 2017 11:09 am
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Post Re: The Astronomy Thread
One day humans will sail among the stars and find it all terribly mundane and boring.
Until then, let's gape at these movies filmed by probes passing beyond where any of us can go, with a sense of childlike wonder.


Thu Jul 13, 2017 11:30 am
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Post Re: The Astronomy Thread
boldilocks wrote:
One day humans will sail among the stars and find it all terribly mundane and boring.
Until then, let's gape at these movies filmed by probes passing beyond where any of us can go, with a sense of childlike wonder.


I´m not that confident. Between the insane amount of resources (specially fuel) it would require plus the extremely long distances...well, I don´t expect a real life Star Trek anytime soon.


Thu Jul 13, 2017 1:42 pm
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Post Re: The Astronomy Thread
raistlin34 wrote:
boldilocks wrote:
One day humans will sail among the stars and find it all terribly mundane and boring.
Until then, let's gape at these movies filmed by probes passing beyond where any of us can go, with a sense of childlike wonder.


I´m not that confident. Between the insane amount of resources (specially fuel) it would require plus the extremely long distances...well, I don´t expect a real life Star Trek anytime soon.

Perhaps not Star Trek.

I am reminded of Elon Musk's comments regarding the Falcon rocket landings, and how he hopes that they will become mundane rather than a huge event, because that'll mean they've become common enough not to care about.

The first sleeper/generation vessel sent to another star STL would certainly be a momentous event. If we started sending one every two years or so? People would accept it as a fact of life.

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Thu Jul 13, 2017 4:52 pm
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Post Re: The Astronomy Thread
hi hi

The two big things that determine the diameter of a gas giant is their mass and there temperature. Theoretical models suggest that Jupiter was twice as large early in its existence, and has been contracting as it cools. But thermal expansion and gravitational compression don't oppose each other in a linear manner. Jupiter would need somewhere between 50 and 75 times more mass to ignite fusion in its core.

EBLM J0555-57Ab is estimated to be cooler than some hot jupiters that have been discovered in close orbits around larger stars, suggesting that its internal fusion is so meager that it isn't doing much to counteract the much greater mass.


Thu Jul 13, 2017 6:57 pm
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Post Re: The Astronomy Thread
Imagine that, this borderline star would see the end of the universe if there was an end to it. Its fusion process is simply too 'slow' to convert enough hydrogen in time.

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Fri Jul 14, 2017 12:07 pm
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Post Re: The Astronomy Thread
GeoModder wrote:
Imagine that, this borderline star would see the end of the universe if there was an end to it. Its fusion process is simply too 'slow' to convert enough hydrogen in time.

Yeah, the smaller the star, the longer it will last.

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Fri Jul 14, 2017 12:26 pm
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Post Re: The Astronomy Thread
GeoModder wrote:
Imagine that, this borderline star would see the end of the universe if there was an end to it. Its fusion process is simply too 'slow' to convert enough hydrogen in time.

So... a nice place to ride out the heat death of the universe?

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Fri Jul 14, 2017 7:29 pm
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Post Re: The Astronomy Thread
At the coldest star in the universe, yeah. :lol:

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Fri Jul 14, 2017 11:08 pm
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Post Re: The Astronomy Thread
hi hi

The latest news in the field of "It might be aliens, but in reality it's almost certainly not." Strange Signals from the Nearby Red Dwarf Star Ross 128 :P


Tue Jul 18, 2017 8:12 am
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Post Re: The Astronomy Thread
Okay. Everyone heard about KIC 8462852? The slowly dimming star that sometimes gets occluded by 'something' orbiting it?

Scientists tried and failed to explain the phenomenon for example by impossibly big asteroid and comet swarms or a secondary brown dwarf orbiting the primary star. All failed to explain one or two other things. For four years, people with Ph.D's and CSc's in astrophysics tried and failed to account for every strange thing that happen around the star and create an overarching theory that could explain dozens of anomalies in one theory. Nothing sticks..but it actually really being Aliens.

Well. Don't be confused anymore. Because the dimming process has now accelerated to an epxonential curve and the star will disappear within twenty years and a hundred/thousand years.

Video summary:
https://www.youtube.com/watch?v=ANSFcswnyAM

TL;DR: It truly seems that someone out there is building a star system sized Dreadstar.

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Wed Jul 19, 2017 2:21 pm
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Post Re: The Astronomy Thread
hi hi

Measure a star for 70 days, make predictions about 20 years in the future. I guess we'll see what happens. :P


Wed Jul 19, 2017 4:19 pm
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Post Re: The Astronomy Thread
Fitting a curve to an irregularly fluctuating set of data points is 20% science and 80% bullshit. You can make the curve look like anything you want.

There could be all kinds of things going on in that system... one or more planets that came too close and were torn apart and are in the process of either falling into the star or being ejected... a chunky proplyd... any phenomenon that is not stable and is in the process of changing. Frankly, I would expect the signature of an artificial structure to be extremely regular, so I don't see how that hypothesis answers any questions.

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Post Re: The Astronomy Thread
I always get suspicious if the main "result" they deliver is a video...

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Wed Jul 19, 2017 10:35 pm
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Post Re: The Astronomy Thread
I'd bet more on a highly variable set of flare cycles, or an orphan black hole orbited by a set of massive clouds, than aliens.


Sat Jul 22, 2017 9:57 am
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Post Re: The Astronomy Thread
And KIC 8462852 continues to be super mega bullshit. Now it has an exponentially dimming downward trend. Jesus Christ!


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Thu Aug 10, 2017 1:24 pm
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Post Re: The Astronomy Thread
HOLY SHIT BATMAN!


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Thu Aug 10, 2017 11:13 pm
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Post Re: The Astronomy Thread
Oh jezus.... We are, from a simple point of explanation, just moving relatively so, that thr accretion disc of Tabby's star is oriented such, that our view passes more and more along thr disc plane, and the angle is getting smaller.
That alone could explain it all.

Bye bye mystery.

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Fri Aug 11, 2017 5:14 am
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Post Re: The Astronomy Thread
Krulle wrote:
Oh jezus.... We are, from a simple point of explanation, just moving relatively so, that thr accretion disc of Tabby's star is oriented such, that our view passes more and more along thr disc plane, and the angle is getting smaller.
That alone could explain it all.

Bye bye mystery.

Accretion disc was considered two fucking years ago and left because there is no fucking IR heat up of dust happening. NONE.

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Fri Aug 11, 2017 10:50 am
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Post Re: The Astronomy Thread
Why should it heat up?
There is no indication that the sun emits more heat than the system radiates, therefore ther is no IR buildup.
They considered a formation of accretion disc.
But I suspect that our viewpoint moves, and that we are now watching more and more along the plane towards the sun, and therefore more and more throigh the middle of the disc.

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Fri Aug 11, 2017 11:35 am
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Post Re: The Astronomy Thread
hi hi

Are fucking years different from regular years? :lol:

At this point, I think a simple accretion disk is not a likely candidate, for the same reasons that an alien mega-structure is not a likely candidate. In a dyson sphere/swarm scenario, IR increases as visible light decreases, as an inescapable requirement of thermodynamics. (If you ask me, the most promising candidate for a dyson sphere/swarm is still object x, in the triangulum galaxy.

At present, I'd put my money either on Tabby's star actually being a complex system of stars, like 4 or more, possibly with rings or accretion disks involved as well. That, or it is a star approaching the end of it's hydrogen cycle.


Fri Aug 11, 2017 5:25 pm
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Post Re: The Astronomy Thread
Krulle: energy input equals energy output. Dust heats up when it absorbs sunlight, and will reach equilibrium when the radiated EM equals the absorbed EM, but with a peak in the IR instead. We're seeing a lot of light being blocked without seeing the expected re-radiated IR that a cloud of dust would have. And KIC 8462852 is over 1200 lightyears from Earth, we'd have to move 20-some light years to change our perspective by one degree.

A Dyson sphere and a disk of rock and dust will both convert visible light to IR, but the Dyson sphere may do so directionally. At the early stages, when it is a collection of structures in belt of similar orbits, the best directions to radiate would be toward the poles, toward the parts of sky most clear of other structures, which would also mean away from anyone seeing the star being occluded by those structures.

However, a simpler answer would be that it's a material that's not heating up. Ices would just sublimate as they absorb heat. We may be seeing an "orbital snowstorm" aftermath of some collision of icy planets a few centuries or millennia ago. There could be multiple ring systems and debris belts involved, clusters of material in elliptical orbits of different periods, etc, explaining the erratic and irregular dimming. This wouldn't last forever, but it's not like we're seeing stars behaving like this all over the place, so it may be we just got lucky with this one. If this is the case, the evaporating material should be visible with sufficiently high-quality spectral measurements.

As far as I'm aware, the star itself being the cause has been ruled out. A star can only change brightness by changing size (which is far too slow) or by changing temperature (which is too slow and doesn't match spectral observations). A star that rapidly dims without major changes in its spectrum is being blocked by something in front of it.


Sat Aug 12, 2017 6:55 am
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Post Re: The Astronomy Thread
Mjolnir wrote:
As far as I'm aware, the star itself being the cause has been ruled out. A star can only change brightness by changing size (which is far too slow) or by changing temperature (which is too slow and doesn't match spectral observations). A star that rapidly dims without major changes in its spectrum is being blocked by something in front of it.
How would my flare or black hole suggestions compare?


Sun Aug 13, 2017 11:27 pm
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Post Re: The Astronomy Thread
Absalom wrote:
Mjolnir wrote:
As far as I'm aware, the star itself being the cause has been ruled out. A star can only change brightness by changing size (which is far too slow) or by changing temperature (which is too slow and doesn't match spectral observations). A star that rapidly dims without major changes in its spectrum is being blocked by something in front of it.
How would my flare or black hole suggestions compare?

Flare activity would be more pronounced and Black Holes would lens the image of the star when orbiting in front of it.

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Mon Aug 14, 2017 5:10 am
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