Rare system of five stars discovered • Hacker News Board

Re: Rare system of five stars discovered

#31

Post by gogoengie » Thu, Jul 09, 2015, 2:38 PM UTC

hfsktr wrote: post #27

I have a question that a simple search didn't answer. Do astronomers actually measure the time it takes a star/planet/whatever to orbit? Or is it simply not possible for things after a certain distance? For example how did they figure out that Pluto takes 247 Earth years per orbit? In our solar system I imagine they could measure it since it's close enough or see it in real time but even Pluto wasn't known for 248 ye…

There are different considerations for the problem: the orbiting masses involved (what is orbiting what?), orbital period (how long for the objects to complete an orbit around their center of mass), the distance of the objects to our measurement device (eg, a telescope on earth), the relative luminosity of the two objects (if they're close together, how do you resolve the darker of the two?), etc.

From all these considerations, there are two problems: 1. Measurement technique (getting the data) 2. System dynamics calculations (analyzing the data)

For measurement, the article mentions both visual and spectroscopic (wavelength) measurements; overviews of these and other techniques are discussed in [1]. You are correct, distance from the measurement device makes things interesting, especially in the presence of atmospheric distortion, but there are lots of tricks that can improve the effective resolution (eg, speckle imaging, which uses a bunch of images taken in rapid succession [2]).

As for the orbital period, think of it like measurements of a line. You don't need every point, just two. If you have several measurements of a celestial body, you can plot them on one of the (MANY) celestial coordinate systems [3] and do some estimates. Longer periods mean more observations for better accuracy, but you don't need to wait for a complete orbital period to get a decent estimate.

Hope this at least gives some useful keywords for your searches!

[1] https://en.wikipedia.org/wiki/Binary_star#Methods_of_observa... [2] https://en.wikipedia.org/wiki/Speckle_imaging [3] http://csep10.phys.utk.edu/astr161/lect/time/coordinates.htm...

Re: Rare system of five stars discovered

#32

Post by hfsktr » Thu, Jul 09, 2015, 3:18 PM UTC

gogoengie wrote: post #31

hfsktr wrote: post #27

I have a question that a simple search didn't answer. Do astronomers actually measure the time it takes a star/planet/whatever to orbit? Or is it simply not possible for things after a certain distance? For example how did they figure out that Pluto takes 247 Earth years per orbit? In our solar system I imagine they could measure it since it's close enough or see it in real time but even Pluto wasn't known for 248 ye…

There are different considerations for the problem: the orbiting masses involved (what is orbiting what?), orbital period (how long for the objects to complete an orbit around their center of mass), the distance of the objects to our measurement device (eg, a telescope on earth), the relative luminosity of the two objects (if they're close together, how do you resolve the darker of the two?), etc. From all these cons…

Awesome thanks. I figured that you didn't actually need to view the full orbit and needed just a few points but for things so far away I thought that it would look practically stationary. Didn't even consider atmosphere...or that there were other factors. Of all the stuff that can be learned it probably isn't high on the list anyways.

Re: Rare system of five stars discovered

#33

Post by antognini » Thu, Jul 09, 2015, 3:45 PM UTC

There is currently some debate about how common these very multiple systems are. It is pretty well known now that about 40-50% of systems are single stars, about 40-45% of systems are binary systems, about 10% are triple systems, and around a few percent are quadruple systems. But it doesn't seem to be well known what fraction of systems are quintuple systems or larger, firstly because they are intrinsically rare, and secondly because the fifth star is usually very hard to find (it tends to be both faint and distant). It seems as though this fraction is probably around 1 percent, maybe a little less. A few years ago it was thought that the fraction of systems with different hierarchies followed a geometric series, but this doesn't seem to be borne out any more as the statistics have improved.

Re: Rare system of five stars discovered

#34

Post by escherplex » Thu, Jul 09, 2015, 4:31 PM UTC

Rexxar wrote: post #30

jeremysmyth wrote: post #11

Earlier quoted context omitted.

You think that's good, try this: Objects can even orbit interesting points in space that are not themselves centers of gravity: https://en.wikipedia.org/wiki/Lagrangian_point

This is linked to orbit around Lagrangian points but it's more surprising: https://en.wikipedia.org/wiki/Horseshoe_orbit

By extension it could be interesting to model the Lagrange-point space topology within this system and probe what object forms might have assembled themselves within the equivalent of L4 and L5 points. Of course, intense mutual solar winds would mitigate against that happening.

Re: Rare system of five stars discovered

#35

Post by krylon » Thu, Jul 09, 2015, 4:54 PM UTC

leni536 wrote: post #13

I would rate this article five stars.

I thought this headline was pure pun-bait, I just didn't think that something so straightforward would work. Thanks for proving me wrong! :)

Re: Rare system of five stars discovered

#36

Post by hobarrera » Thu, Jul 09, 2015, 11:29 PM UTC

lagadu wrote: post #8

Ok, so objects orbit not other objects but rather centres of gravity. This means that the system in question could have planets with small orbits (like the earth's for example) orbiting that system's centre of mass despite the stars being many AUs away from it. It may be unlikely but it's certainly possible, right? Am I missing something that'd make this impossible? Because that would be incredibly cool! edit: I'm as…

I wonder is there can be a small planet at the gravitational centre of this system, of if it's be ripped apart by the stars on each side.

Re: Rare system of five stars discovered

#37

Post by mixmastamyk » Wed, Jul 15, 2015, 7:36 AM UTC

mixmastamyk wrote: post #7

INTPenis wrote: post #5

Oh my five suns. ;) >The pair of stars orbit around a mutual centre of gravity, but are separated by more than the distance of Pluto's orbit around the Sun. But what could they be orbiting around?

Their center of gravity, say about here: o O---------------o ^ Pluto and Charon do it as well, even Earth and Moon to a small degree.

http://www.abc.net.au/cm/lb/6605566/data/jupiter-and-io-take...