37
votes
Can a magnetic field of an object be stronger than its gravity?
It depends on what object it's acting on. There are many objects, including stars, that have magnetic fields where Lorentz forces on charged particles like electrons and protons are stronger than the ...
- 5,336
30
votes
Accepted
Do the axes of rotation of most stars in the Milky Way align reasonably closely with the axis of galactic rotation?
There is very likely to be a random scatter.
Unlike planets orbiting the Sun in the Solar System, most of the stars in the Galaxy did not form at the same time as the Galaxy itself. There is therefore ...
- 159k
20
votes
Accepted
Is any 3 body system known?
Answering in the spirit of the question, I think he's asking if there is ever a chaotic 3 body system that's long term stable, or, to put it another way, a 3 body system without a standard hierarchy ...
- 24.2k
17
votes
Accepted
Can a magnetic field of an object be stronger than its gravity?
Let's look at the proper magnetic force (as opposed to the Lorentz force on a moving, charged object described in @KenG's answer) on a specimen $S$ of magnetized material with mass $M_S$ as a way to ...
- 30.5k
12
votes
What does this tweeted Astronomy Plot of the Week mean? What does it represent?
TLDR;
Its a diagram showing all the physics and modeling choices that go into different models (the colored boxes in the middle) to compute an SED.
Longer answer:
First a SED is a spectral energy ...
- 2,075
12
votes
Accepted
Why do stars born in a cluster finally disperse?
The boundedness or otherwise of clusters remains to be established in most cases. The vast majority of clusters become unbound and disperse at a much younger age than the Pleiades. Or they may be born ...
- 159k
10
votes
Is any 3 body system known?
The three body problem is a theoretical problem in Newtonian mechanics. It is possible to solve, exactly, the two body problem: Both bodies move in conic sections, typically ellipses, relative to ...
- 127k
9
votes
Can a magnetic field of an object be stronger than its gravity?
It isn't impossible, but the short answer is "no".
A gravitational field will accelerate all matter and energy equally while a magnetic field will only accelerate moving electric charges (other ...
- 91
9
votes
Accepted
Are the stars outside of the galactic plane in the galactic halo?
The galactic disk, as Riley Jacob wrote, has a definite thickness. It's actually composed of a thin disk $\sim0.3\text{ kpc}$ thick and a thick disk $\sim1\text{ kpc}$ thick, at least (McMillan (2011) ...
- 37.3k
7
votes
Are the stars outside of the galactic plane in the galactic halo?
I'll turn this around for you. The brightest star that is classed as a "halo" or metal-poor population II star is HD 140283, with a visual magnitude of 7.2 and not even visible to the naked eye. Even ...
- 159k
7
votes
Accepted
Is the three-body system "unique"?
What you're really asking about is less to do with Astronomy and more to do with mathematics. You're basically asking if, given a system of differential equations, will a unique solution exist for all ...
- 15.1k
7
votes
Accepted
Does the Final-Parsec problem apply to stellar collisions?
The "final parsec problem" describes the difficulty in getting two supermassive black holes close enough together that their merger timescale due to gravitational wave emission becomes ...
- 159k
6
votes
Accepted
What does this tweeted Astronomy Plot of the Week mean? What does it represent?
SED fitting
SED fitting is the practice of inferring physical properties of a stellar population (a galaxy, a cluster...) from measures of the Spectral Energy Distribution.
The spectrum of a stellar ...
- 4,481
6
votes
Accepted
What is convection overturn?
The convective overturn time is the typical timescale for a convective cell to rise in a gas. Imagine a "lava lamp" - it's the time for one of the blobs to rise from its lowest to highest point.
I am ...
- 159k
6
votes
Is any 3 body system known?
There are many systems with 3 and more bodies, but more or less universally they are highly hierarchical systems that behave approximately like a bunch of two-body systems. For example:
The solar ...
- 132
6
votes
List of Moving stars on the northern hemisphere? [Stellar kinematics]
What you're looking for is stars with "High Proper Motion". A Google search of "High proper motion stars" will provide a number of such lists. A quick look at Wikipedia gives this link:
https://en....
- 61
5
votes
Accepted
Why aren't stars like Eternally Collapsing Objects?
We know that stellar radiation pressure balances the gravitational compressive forced of a star.
We do not know that. Degeneracy pressure, thermal pressure, and radiation pressure are what ...
- 34.4k
5
votes
Accepted
how far away can close stars diverge with time?
Only one force counts on galactic scales: gravity.
Stars like Alpha Centauri are orbiting in the galaxy, as is the sun. Both stars are moving in a similar direction and at roughly the same speed, ...
- 127k
5
votes
Is any 3 body system known?
Yes, there are triple star systems, bound by gravity, that seem stable. See a list here:
https://en.wikipedia.org/wiki/Category:Triple_star_systems
There are also systems with 4 stars or more, ...
- 18.3k
4
votes
Accepted
Is it possible for stars not to rotate?
No, this is not possible.
During the stellar formation, some angular momentum will always be present. And any "braking" effects (magnetic, relativistic, tidal etc.) will become weaker as the rotation ...
- 800
4
votes
List of Moving stars on the northern hemisphere? [Stellar kinematics]
SIMBAD allows you to search for stars given various criteria.
I searched for:
Dec > -20 (easily visible from most locations in the Northern hemisphere)
Vmag < 4 (easy naked eye objects)
pm > ...
- 127k
4
votes
Accepted
Examples of astrophysical objects NOT in virial equilibrium?
Not clear what the initial part of your question means. Objects can be in virial equilibrium without being in thermal equilibrium.
A clear exception to the virial theorem would be any system that is ...
- 159k
4
votes
If a cluster of stars in dynamical equilibrium falls into a much larger blob of dark matter, will it get hotter and expand? Will it stop?
Yes, what you are proposing is essentially the accretion of dwarf galaxies/globular clusters onto larger bound objects. As the gravitationally bound cluster falls towards the more massive object, it ...
- 436
3
votes
Ellipticals supported by random motions
The same way rotation does. If you look at each star, it is following some kind of orbit, so it has a motion. The only difference between a spiral and an elliptical is that the motions in a spiral ...
- 5,336
3
votes
Accepted
Dynamical modelling of galaxies with counter-rotating components using the Schwarzschild method
Convert the 3D luminosity distribution to mass using a bunch of mass particles.
Well, you probably could do that, but I suspect it would be inaccurate and extremely time-consuming. Most Schwarzschild ...
- 18.1k
3
votes
How is phase defined in a binary orbit with eccentricity?
Usually, how is phase=0 defined? It is relative to the line of apses perhaps with phase=0 at periastron?
The true anomaly, $\theta$, is the angle between the current location of the orbiting particle ...
- 4,533
3
votes
Do low-mass red giants last longer than high-mass red giants?
Higher mass stars will have shorter lives. Even though they have more fuel for nucleosynthesis, they burn this fuel much quicker than lower mass stars.
Generally, you should think of "red-giant&...
- 41
3
votes
Can our solar system ever be farther than Rigel from the center of the galaxy?
I don't think it can, in the "near" future. The Sun has a velocity component of about 10 km/s towards the Galactic centre, but Rigel has a radial velocity of about 20 km/s away from the Sun.
...
- 159k
2
votes
How is phase defined in a binary orbit with eccentricity?
Moreno et al. in their paper Eccentric binaries: Tidal flows and periastron events [2011] define the orbital phase as from -0.5 to 0.5, where periastron is at phase 0, and apastron is at -0.5 and 0.5. ...
- 16.3k
Only top scored, non community-wiki answers of a minimum length are eligible