4 ms·

is this not normal? Like how planets will orbit a mass of star or black hole at a certain distance depending on their speed?

samschooler 9y ago
I’d actually love to get an explanation for this. Do galaxies work similar to solar systems in that all objects are in orbit around a central mass or is it a different phenomenon that binds matter together into a galaxy?
- Merad 9y ago
  I believe the current theory is that most (all?) galaxies have a supermassive black hole at their heart.
  - muthdra 9y ago
    Yeah, or so I heard. What's the cause and effect order for galaxies and their corresponding supermassive black holes?
- kwoff 9y ago
  Planets orbit around the center of mass. It's coincidental that the center of mass is (at least in our case) at the sun's location, because the sun has most of the mass.
- mutagen 9y ago
  The mass of the central black hole is a tiny fraction of the mass of the galaxy, it might be more correct to say that the objects in a galaxy orbit the common mass (including dark matter) of the galaxy. For example, the black hole at the center of the Milky way is estimated at 4.1×10^6 M (solar mass) and the total Milky Way mass is estimated at 0.8–1.5×10^12 M (figures from Wikipedia). Some interesting articles found while digging for these numbers: https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html https://academic.oup.com/mnras/article/420/4/3621/975383 https://academic.oup.com/mnras/article/420/4/3621/975383 https://academic.oup.com/mnras/article/414/3/2446/1042117 https://academic.oup.com/mnras/article/414/3/2446/1042117
failsafe 9y ago
Curiously, the turning effect we observe is not coming from stars moving in an orbit around the centre of the galaxy. When we plot the movement of the light coming from the spiral arms (or bar) of a galaxy, given their size and speed of movement it would require the stars to be moving faster than the speed of light. Also if the spiral arms were made up of orbiting stars, the ones closer to the center would move faster than the outer stars causing a winding effect, which we do no observe. One theory suggests that we are observing a density wave sweep through material, which causes compression and heat, increasing the likelihood of new stars to be born, these stars burn bright and white. As this wave passes through, it leaves behind those stars in its wake, which over time burn less brightly than before. One analogy that comes to mind an electronic circuit, although electricity travels at the speed of light, the actually charge carriers are moving relatively slowly, know as the drift velocity.
- deleted 9y ago
  [deleted]
- michaelsbradley 9y ago
  Homopolar motor, maybe?
  - 8bitsrule 9y ago
    I was just going to say: all 33-1/3 rpm records - regardless of their thickness or chemistry - are observed to rotate at about the same rate, regardless of record size. And (I'll note that) the drive belts are usually hidden from view.
    - michaelsbradley 9y ago
      Interesting... http://www.ptep-online.com/2018/PP-53-01.PDF http://www.ptep-online.com/2018/PP-53-01.PDF

samschooler 9y ago

I’d actually love to get an explanation for this. Do galaxies work similar to solar systems in that all objects are in orbit around a central mass or is it a different phenomenon that binds matter together into a galaxy?

Merad 9y ago
I believe the current theory is that most (all?) galaxies have a supermassive black hole at their heart.
- muthdra 9y ago
  Yeah, or so I heard. What's the cause and effect order for galaxies and their corresponding supermassive black holes?
kwoff 9y ago
Planets orbit around the center of mass. It's coincidental that the center of mass is (at least in our case) at the sun's location, because the sun has most of the mass.
mutagen 9y ago
The mass of the central black hole is a tiny fraction of the mass of the galaxy, it might be more correct to say that the objects in a galaxy orbit the common mass (including dark matter) of the galaxy. For example, the black hole at the center of the Milky way is estimated at 4.1×10^6 M (solar mass) and the total Milky Way mass is estimated at 0.8–1.5×10^12 M (figures from Wikipedia). Some interesting articles found while digging for these numbers: https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html https://academic.oup.com/mnras/article/420/4/3621/975383 https://academic.oup.com/mnras/article/420/4/3621/975383 https://academic.oup.com/mnras/article/414/3/2446/1042117 https://academic.oup.com/mnras/article/414/3/2446/1042117

failsafe 9y ago

Curiously, the turning effect we observe is not coming from stars moving in an orbit around the centre of the galaxy. When we plot the movement of the light coming from the spiral arms (or bar) of a galaxy, given their size and speed of movement it would require the stars to be moving faster than the speed of light. Also if the spiral arms were made up of orbiting stars, the ones closer to the center would move faster than the outer stars causing a winding effect, which we do no observe. One theory suggests that we are observing a density wave sweep through material, which causes compression and heat, increasing the likelihood of new stars to be born, these stars burn bright and white. As this wave passes through, it leaves behind those stars in its wake, which over time burn less brightly than before. One analogy that comes to mind an electronic circuit, although electricity travels at the speed of light, the actually charge carriers are moving relatively slowly, know as the drift velocity.

deleted 9y ago
[deleted]
michaelsbradley 9y ago
Homopolar motor, maybe?
- 8bitsrule 9y ago
  I was just going to say: all 33-1/3 rpm records - regardless of their thickness or chemistry - are observed to rotate at about the same rate, regardless of record size. And (I'll note that) the drive belts are usually hidden from view.
  - michaelsbradley 9y ago
    Interesting... http://www.ptep-online.com/2018/PP-53-01.PDF http://www.ptep-online.com/2018/PP-53-01.PDF