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Hornblower
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29 Mar 2017 19:11

Quontex, by using https://www.planethunters.org/ Pretty cool raw Kepler data that you can analyze.
Here's one of the transits of the possible exoplanet:
exoplanet2.png

No but seriously, can anyone calculate some stuff?
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Watsisname
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29 Mar 2017 21:20

Ultimately to determine if this is a plausible planet you would need to to perform some kind of chi-square test, to see if what you think is a transit is statistically significant, or how probable it would be to observe similar events from data which actually do not contain transits.  But taking the data as they are,

since all you have is information from transit method, the best you can do for determining the planet's mass is constrain it by the Mass-Radius relation for solid planets.  If the planet is 2.6 Earth Radii, it's pretty implausible to be a solid iron planet (it would have to be hundreds of Earth masses), or even a silicate planet (would have to be at least 20 Earth masses).  More likely it is a water planet.

We can do better for the orbital distance.  To do it, determine the mass of the star from available data, and then apply Kepler's Third Law.

Based on the KIC catalog data, the star has an effective temperature of 4741K, plus or minus 200K, and a radius of 0.831 solar units.  That would make it a K-class star.  We can find the star's luminosity in solar units by

Image

which comes to 0.315 +/- 0.05 Suns.  Then by the Mass-Luminosity relationship,

Image

we find the star's mass to be 0.749 +/- 0.032 Suns.  Apply this to Kepler's Third Law:

Image

where G is the gravitational constant, M is the star's mass, and T is the planet's orbital period, 

and we find the planet's semimajor axis is 0.305 +/- 0.004 AU.

Now that we have the planet's distance and the star's luminosity, a fun calculation is to find the planet's surface temperature (assuming the planet is a blackbody -- albedo and/or greenhouse effect can of course change it)

Image

where AB is the planet's albedo, a is again its semimajor axis, ε is a greenhouse parameter (between 0 and 1, smaller makes it stronger) and σ is the Stefan-Boltzmann constant.

This tells us that an earth-like planet in that orbit would have a surface temperature of about 400K.  Pretty warm!
 
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Gnargenox
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29 Mar 2017 21:27

A buddy of mine wrote this program to look for exoplanets using similar data sets. He has managed to duplicate the findings of 2 planets around 47 Ursae Majoris with data that is a decade old. A simple equation used by the program:

47 Ursae Majoris.jpg


The equation for the radial velocity of a star with n planets, with K_i being the i-th planet's RV semi-amplitude (which you can use to get its mass), ε_i is the i-th planet's eccentric anomaly (the location of the planet around its orbit after you take eccentricity into account), ω_i is the i-th planet's longitude of periapsis, and γ is just some offset between the observer and the star.

[math]
 
Upsilon Andromedae, which has both a hot Jupiter and a planet at ~1200 days, was hard to see anything because the hot Jupiter's signal flooded the screen with rapid short-wavelength chaos. Eventually the program will do Newtonian fitting for characterizing planet-planet interactions, transit modelling and the Rossiter-McLaughin effect. Obviously needs to add ability to analyze bisector widths and full-width-at-half-maximums for the spectral lines for a sanity-check to make sure the signals you detect aren't the star trolling you. He also has to figure out detrending and noise management, too. He was completely unable to recover the planet around Lalande 21185 reported last month.

In the right panel he was folding at various orbital periods trying to see a coherent signal by eye (since there isn't any periodgram capability yet). At the bottom you see a few bad data points were pruned because they were quite different from the rest of the data set.

folding.jpg


Here is 51 Peg b. Obviously there are ways to improve how data is presented. Multi-planet systems where orbital periods vary quite a bit is alot harder. Imagine if 51 Peg had a second detectable planet (or take the real example of WASP-47). The first panel would be a freaking mess, lol. Still needs to be able to fit to residuals or subtract signals.

51 Peg b.jpg


I only mention this because he might release a beta soon and might have a link where you can download and use it to do calculations.
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Gnargenox
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29 Mar 2017 21:32

I'm having trouble getting the math code to show up so here is a pic
formula.png
formula.png (2.33 KiB) Viewed 528 times
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Watsisname
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29 Mar 2017 23:18

Yeah, the math code seems to have been broken for a while. =(  That looks like a nice bit of software your buddy made!
 
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30 Mar 2017 03:45

Watsisname, thank you so much  :D
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30 Mar 2017 16:55

If you had a device that can change 1 thing about astronomy and astrophysics, what will it be?
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marciostavares
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30 Mar 2017 17:26

Hello everyone!

In the Interstellar movie, when they get close to the Miller's planet (the first after passing through the wormhole), we can see there's a relatively small distance between the ship and the planet (of course it would have been shortened for better visual effect) and there's a considerable difference in the time-shift between the two points (1 hour at Endurance equals to 7 years at the planet).

My question is (I'm sorry if it's a silly one): what would we see if we could put a telescope in the ship and point it to the surface of the planet? Would we see the crew and everything down there moving very slowly? Would it be possible to see anything at all?

The same applies to the ship traveling around Gargantua, when they say that slingshot maneuver would cost them 51 plus Earth-years. If a perpendicular observer (outside the time-shift) could see the entire movement, what would be the outcome for him? Would he see the ship fast approaching the black hole and then "slowing down" (or even "disappearing"??) and then coming out in the other side only 51 years after??

I can't visualize it as it's very strange to me.

I would like to thank everyone in advance for you time and patience to answer that :)
 
marciostavares
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30 Mar 2017 17:28

Correcting: 1 hour at the planet equals to 7 years at the Endurance :)
 
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Watsisname
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30 Mar 2017 19:05

marciostavares,

I think the extreme time dilation at Miller's planet is due to being so close to the black hole (you must be very close to the event horizon for the time dilation to be that significant), and not so much a property of the planet itself.  But at any rate, if you were to look at the planet from far away, what would it look like?

Actually, you wouldn't see much of anything!  Just the dark abyss of the black hole.  The reason is because gravitational time dilation goes hand in hand with gravitational redshift (the light gets stretched as it climbs out of the gravitational well), and for one hour to be dilated to 7 years corresponds to the light being stretched by a factor of over 61000.  This would turn visible light into microwaves (centimeter wavelengths), and the light would also be dimmed by the same factor.

So to your eye you would just see darkness, but perhaps a very sensitive microwave telescope could pick out the radiation, in which case you would indeed observe the planet and everything on it evolving very slowly.

marciostavares wrote:
Source of the post The same applies to the ship traveling around Gargantua, when they say that slingshot maneuver would cost them 51 plus Earth-years. If a perpendicular observer (outside the time-shift) could see the entire movement, what would be the outcome for him? Would he see the ship fast approaching the black hole and then "slowing down" (or even "disappearing"??) and then coming out in the other side only 51 years after??

Basically, yeah.  Their clocks slowing down with respect to yours would again correspond to their light being reddened and dimmed to invisibility.  It would seem as if they just vanished near the event horizon, but then if you waited around for another 51 years you would see them emerge, since they didn't actually cross it, but passed very close to it.

marciostavares wrote:
Source of the post I can't visualize it as it's very strange to me.

I know right? :)  Relativity is one of the weirder, counter-intuitive, and seemingly fantasy parts of physics.  But it's totally a real thing and it applies everywhere, not just near black holes or close to the speed of light.  If you are near sea level, time for you passes more slowly than it does for someone who is at higher elevation, because the gravitational field is stronger for you.  Time passes about 10 nanoseconds per day more quickly with every 1000m elevation that you gain, and this is actually measurable! 
 
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DoctorOfSpace
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30 Mar 2017 19:12

marciostavares,I recommend reading the book by Kip Thorne called The Science of Interstellar, it covers a lot of the interesting aspects of the film and the compromises made in regards to realism.

And to go along with what Watsisname said, here is a visualization to give you an idea on how close Miller's planet is supposed to be
Image
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midtskogen
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30 Mar 2017 23:33

NIL DIFFICILE VOLENTI
 
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Watsisname
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31 Mar 2017 02:19

Interesting!  I think they have a good motivation, in that they are looking at whether accelerated expansion necessarily requires dark energy, or if the local distribution of matter -- which ordinarily we treat as homogeneous and isotropic because it makes the math easier, and is justified on large scales -- could actually have effects on large scales that happen to mimic the effects of dark energy.

If the latter is correct then it's a pretty amazing coincidence, because the standard (Lambda-CDM) model agrees with observations really well. Plus it's not just accelerated expansion that acts as a test for dark energy, but the precise way that the expansion rate changes over time.  Dark energy also affects the universe's spatial curvature, the evolution of the cosmic web, and the apparent size of the fluctuations in the CMB.

This team's model produces a very similar history for the expansion rate over time.  It agrees with supernovae data (apparently slightly better than the Lambda-CDM model).  Which is surprising and quite promising!  The caveat is that their model is based on a conjecture about how small scale density fluctuations scale can be treated in cosmology, and it ignores tidal forces.  So I'm not certain how reliable these results really are.  They also haven't yet investigated the spatial curvature, or the CMB angular power spectrum, which would be really good observational tests.  Instead they are focusing simply on the expansion history after z~9.

So in a nutshell I think the study is very compelling, but of course more work and verification is required.
 
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31 Mar 2017 10:56

Universal_Explorer wrote:
Source of the post If you had a device that can change 1 thing about astronomy and astrophysics, what will it be?

I don't know... If i could choose 2 things i would choose teleportation and invincibility (at will, i don't want to be invincible all the time). However one thing... That's difficult. I would probably take being able to change conservation of mass/energy law (that law that prevents matter/energy from appearing out of nowhere) so i could transform. :)
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John Boone
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10 Apr 2017 14:01

i have a quick question that might be fun: if the rings of Saturn were magically given the mass of Saturn, what chaos might ensue over the next few days/weeks/months?
Maybe it’s a little early. Maybe the time is not quite yet. But those other worlds — promising untold opportunities — beckon. Silently, they orbit the Sun, waiting -Carl Segan

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