M10 - Orbits - Deep Sky Videos

so I looked through the literature I looked at what was known about m10 and I thought it would make a really interesting example of how we talk about how objects orbit other objects so all the stars in m10 are orbiting around the center of mass and and they're they're mostly gravitationally bound but and ten itself is orbiting around our galaxy so just like our solar system the earth is orbit around the Sun but the Sun is then orbiting around the center of our galaxy in the disk of the galaxy and that's the slight difference with m10 the globular clusters are mostly located outside the disk so if you think of the galaxy is kind of a fried egg of a disk of stars and gas and dust with a bulge in the middle and the globular clusters are are located mostly out in the halo where all the dark matter is but what's interesting is the same physics governs everything everywhere and so if you think about the orbits of the planets around the Sun we can actually describe those orbits in six numbers which I find kind of interesting it really comes down to following mostly Kepler's laws laws of physics that have been known for hundreds of years and reducing those motions to a few numbers Kepler's first law with respect to the solar system is that planets orbit the Sun in an elliptical path with the Sun at one focus so that's the most most undergraduate physics students would hopefully be able to tell you that so what that means is if this is your orbit here the first number that you have is the eccentricity and that says how much how different that orbit is from an ellipse so in this case we can stretch it out and make it very elliptical or sort of elliptical the next thing you can do is measure some have some sort of measure of the size of the orbit we measure that by the semi-major axis the length of the longest part of the ellipse so you can imagine I could stretch this out if I could keep it as an ellipse you'd have a bigger orbit or a smaller orbit so that's two the third number that you can have is the inclination so if you imagine some reference plane like for example this table you could incline that orbit through any number of angles number four it's probably my favorite because it's called the longitude of the ascending node which is a great name as whatever object is going around this elliptical orbit at some point it's going to come up through the plane of that reference plane okay and so that we do you know that's an arbitrary point to pick but you you say what angle does that make going round like this and that fixes it in that dimension and then the fifth is the argument of periapsis these are great names and that just means again you pick up a fixed reference point and periapsis means the closest point to the center of the orbit so you know if you think of the solar system that would be perihelion closest to the Sun if it's around a star it would be periastron around the galaxy it's perry galactic own but the general name is periapsis and so what that means is that you can then rotate in that plane and fix the orientation of the orbit that way and that gives all of your spatial orientations makes them all fixed and the sixth one adds the element of time and that just says at a given time you just need to say at one point in time where the object is in that orbit and then that fixes the entirety of that elliptical orbit gives you like a start point to look forward or back from exactly you just specify your time where it is at that point and and you're done but and then this is where m10 comes in is that sometimes those orbits don't stay fixed so there's lots of ways you could perturb an orbit and make it change a bit so that fifth element that I mentioned the argument of periapsis that can change and we have a very famous example of that which is the perihelion the precession of the perihelion of mercury we could for a long time trace Mercury's orbit very well but even accounting for all of the other perturbations of all the other planets etc there was still one unexplained movement in that orbit change in that orbit over time that couldn't be explained and that ended up being one of the first proofs of general relativity going back to M 10 talking about the solar system but M 10 this globular cluster orbits the galaxies in a slightly inclined orbit it occasionally plunges down through the disc and is up through the other side what does that plunge through the dish is that a hazardous time or is the disk so empty in itself that it could just happily wander through without smashing into anything well it's not gonna smash into anything spaces extraordinarily empty but it does not come unscathed and that's that's actually the route that I took in to finding the information about this because I found this paper which is called the effect of tidal shocks on the evolution of globular clusters in this paper they asked exactly that question how dangerous is it for a globular cluster to pass repeatedly through the plane of the galaxy and it turns out it is pretty dangerous but not through direct collisions through tidal effects and and that means the gravitational stripping of stars in the outskirts of the globular cluster as it passes through the plane of the disc well first of all I was quite astonished to realize that you we could actually model the orbits of globular clusters the example they use in this paper is m10 and they actually provide a model for the orbit why are you astonished by that I would have thought it was obvious we can model all sorts so they can model galaxies and also we can but anything involving time yet we haven't been along for around very long to make observations and things on the sky most of them don't move very fast this globular cluster it takes 150 million years to complete one orbit so it actually turns out that those measurements are made using photographic plates that go back 80 or a hundred years that's the timescale that you need but even then that has to be tied to a very accurate reference frame because you you can't in everything everything is moving a little bit so you need to you need to have a very well-established reference frame you get some really neat patterns in the orbit so I mentioned that you know orbits of things often proceed in a very you know fixed elliptical fashion but sometimes as I mentioned that ellipse can get perturbed and so what you're seeing here is the position over time of m10 presented in a funny way so on this axis you have radius from the center of the galaxy so that's how far it from the center and so it's going in and now you know it's it's changing its its position with respect to the center of the galaxy how far away it is Zed represents the distance above and below the disk so sometimes it's up here and then it passes through and it goes down on the other side and so both of these motions are happening at the same time but if it was just on a little ellipse it would follow the same pattern over and over again and clearly it's not something is is perturbing it and making it change and if we think back to our orbital elements that means that the argument of the periapsis is changing and I can demonstrate that really easily with this fun toy for everyone's childhood because I don't know you don't know that you did not have a spirograph no I didn't oh that's crazy if you set this up you can produce an orbit that looks like an ellipse right but it's actually not quite doesn't quite come back to the same point and if we follow that through time that changes and makes a pattern and in this case this is exactly what's happening to m10 so it's ellipse is shifting by a little bit every time and it Oh BAE is called rosette nebula

Channel: DeepSkyVideos

Views: 79,420

Rating: 4.9760122 out of 5

Keywords: astronomy, Messier 10 (Celestial Object), Orbit (Orbit Type), Messier Object

Id: 8SRJIc6biXQ

Length: 8min 19sec (499 seconds)

Published: Wed Nov 25 2015

Reddit Comments

[u/basec0m]

Very interesting... thanks for posting.

[u/doctorlogical]

Paging /r/kerbalspaceprogram

But seriously - I need me a spiralgraph.