Exploring the Impact of Dark Matter on Galaxies and Solar Systems

In summary, galaxies spin differently than the solar system, with a nearly constant speed throughout. Dark matter, which is spread out and low in density, accounts for this difference in spin by contributing more mass as you go farther out in the galaxy, allowing for the orbital speeds to remain constant. However, dark matter does not have a significant effect on the solar system due to the high concentration of regular matter. Additionally, dark matter cannot shrink or fall into the center of galaxies due to its lack of collisions.
  • #1
nhmllr
185
1
Okay, so I understand that galaxies spin more like a frisbee than the solar system, and that there is evidence for a lot of non-light-emitting mass (such as gravitational lensing) but how would dark matter account for the difference in the spin of galaxies? Gravity still decreases inverse to the square of the distance, right? And also, why wouldn't dark matter have an effect on the solar system, where pluto would orbit in one Earth year?
 
Astronomy news on Phys.org
  • #2
nhmllr said:
Okay, so I understand that galaxies spin more like a frisbee than the solar system, and that there is evidence for a lot of non-light-emitting mass (such as gravitational lensing) but how would dark matter account for the difference in the spin of galaxies?
Actually, spiral galaxies don't spin like frisbees either. The solar system orbits such that farther planets from the center are slower, and frisbees spin such that farther places from the center are faster. Galaxies spin with nearly constant speed everywhere-- so the analogy there might be joggers on a circular track, assuming people generally jog at a similar speed.
Gravity still decreases inverse to the square of the distance, right?
Yes, the difference is not in the nature of the gravity, it is in the nature of the mass distribution. When we have gravity that falls like distance squared for an entire mass distribution, it means the mass distribution is highly centrally concentrated, almost like a point of mass at the center. But if the mass distribution is very spread out, such that a lot of the mass is actually at larger radius than the point in question, then only the mass interior to the point in question contributes to the gravity there (the rest canceling if it is a spherically symmetric distribution). So as you go farther out in the galaxy, more of the dark matter mass contributes, because the dark matter is very spread out (unlike the stars, which are centrally concentrated). That's the key to allowing the orbital speeds to stay the same-- more mass contributing to holding them in, as you go farther out.

And also, why wouldn't dark matter have an effect on the solar system, where pluto would orbit in one Earth year?
Because dark matter is relatively low density, regions where the regular matter is concentrated, like solar systems, can ignore it.
 
  • #3
Ah, I see. But then why wouldn't the dark matter just fall into the centers of galaxies?
 
  • #4
It is falling all the time-- but it can't lose energy, so it cannot shrink. It just falls right on past and keeps on going-- like an orbit. Exactly like an orbit.
 
  • #5
Ken G said:
It is falling all the time-- but it can't lose energy, so it cannot shrink. It just falls right on past and keeps on going-- like an orbit. Exactly like an orbit.

Oh, like a pendulum. Makes sense, thank you!
 
  • #6
Dark matter is collionless. It falls in, but, without collisions to slow it down, it just shoots right back out again. IOW - what Ken said.
 

1. What is dark matter and how does it impact galaxies?

Dark matter is a type of matter that does not interact with light and cannot be directly observed. It is believed to make up approximately 85% of the total matter in the universe. Dark matter has a significant impact on galaxies as it provides the gravitational force that holds galaxies together. Without dark matter, galaxies would not have enough mass to maintain their shape and rotation.

2. How does dark matter affect the formation of galaxies?

Dark matter plays a crucial role in the formation of galaxies. Its gravitational force attracts regular matter, such as gas and dust, which eventually clumps together to form stars and galaxies. Without dark matter, the universe would look very different, with fewer galaxies and less structure.

3. Can dark matter impact our solar system?

Yes, dark matter can have an impact on our solar system. While it does not directly interact with regular matter, it does exert a gravitational force on it. This can affect the orbits and movements of objects within our solar system. However, the effects of dark matter on our solar system are minimal compared to its impact on galaxies.

4. How do scientists study the impact of dark matter on galaxies and solar systems?

Scientists use a variety of techniques to study the impact of dark matter on galaxies and solar systems. These include observing the rotation of galaxies, measuring the gravitational lensing effect, and studying the distribution of matter in the universe. Scientists also use computer simulations to model the behavior of dark matter and its effects on galaxies and solar systems.

5. Is there a way to detect or directly observe dark matter?

Currently, there is no way to directly observe or detect dark matter. However, scientists are continually researching and developing new methods to study dark matter, such as using high-energy particle detectors and searching for dark matter annihilation products. These efforts are crucial in helping us understand the impact of dark matter on galaxies and solar systems.

Similar threads

Replies
10
Views
1K
Replies
14
Views
1K
  • Astronomy and Astrophysics
Replies
22
Views
5K
  • Astronomy and Astrophysics
Replies
6
Views
2K
  • Astronomy and Astrophysics
Replies
5
Views
2K
  • Astronomy and Astrophysics
Replies
22
Views
5K
  • Astronomy and Astrophysics
Replies
10
Views
1K
  • Astronomy and Astrophysics
Replies
4
Views
2K
  • Astronomy and Astrophysics
Replies
6
Views
1K
  • Astronomy and Astrophysics
Replies
2
Views
2K
Back
Top