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Shailesh Pincha
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What is the density of galactic centre? Thus what form of Kepler's law account for the galaxy rotation curve increasing near the galactic centre?
It's speculated that there exists Supermassive Black Holes at the centre of the galaxies. So wouldn't the mass density obtained by the value, 1600stars/light year, be too great compared to the calculated and assumed density of the SMBHs.Janus said:At the core, the density can be ~1600 stars/cubic light year. As far as the rotation curve near the center, I assume you are asking about why the orbital speeds increase with distance from the center in the region of the bulge. For this, you have to use Newton's laws of gravity instead of Kelper's laws. Kepler's laws work when the mass being orbited is fixed and unchanging. This is not the case for stars orbiting in the central bulge of the galaxy. For them, the mass they are orbiting is the mass of all the stars closer to the center then they are. Thus the further from the center they are, the larger the mass that is effecting their orbital speed. More mass means a larger speed. In the central bulge region this increase in the mass overrides the increase in distance which would tend to decrease orbital speed.
Once you get outside of the bulge, the star distribution changes to being disk-like rather than spherical, this decreases how much the mass increases with orbital distance, and the distance begins to have a stronger influence on the orbital speed. If the only mass of in the galaxy were due to that those parts of it we see, the orbital speed should begin to fall off with distance, The fact that they don't and tend to stay fairly constant and are higher than they should be for the visible mass we see indicates that there is mass there that we do not see and that its distribution does not match that of the visible matter.
The galaxy centre is the point at the heart of a galaxy where most of its mass is concentrated. It is determined by observing the distribution of stars and gas within the galaxy and calculating their gravitational pull towards the centre.
The rotation curve of a galaxy is a graph that shows how the orbital velocity of stars and gas changes with distance from the centre. By analyzing this curve, scientists can determine the mass distribution of a galaxy, as the rotation speed depends on the mass of the galaxy and its distribution.
No, the rotation curve of each galaxy is unique and depends on its mass distribution. Some galaxies have a flat rotation curve, while others have a steeply rising or falling curve. This can provide important insights into the structure and evolution of the galaxy.
Dark matter is an invisible, elusive substance that is thought to make up a large portion of a galaxy's mass. Its gravitational pull affects the rotation curve, causing it to rise and flatten out at greater distances from the centre. This helps scientists estimate the amount of dark matter present in a galaxy.
The rotation curve of a galaxy can provide important clues about the nature of gravity and its role in the universe. If the curve does not match the predictions of Newtonian gravity, it may indicate the need for a new theory, such as Einstein's theory of general relativity, to explain the motion of objects within a galaxy.