Why are MACHOs in the Halo not the disk

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In summary, the reason for looking for massive compact HALO objects is because we know there is unobserved material in the halo, and the rotation curves of galaxies are not sensitive to extra matter near the core. The disk is considered part of the halo, so any dark matter in the disk is also in the halo. The most likely explanation for the constant rotation speed of galaxies is that there is a lot of mass in the halo outside of the visible disk. This is why people are looking for MACHOs, as they could be located in the halo outside of the visible disk according to equations.
  • #1
Daniel_G
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Hi, I was just wondering, why are we only looking for massive compact HALO objects?

Can there not be such objects in the Galaxys disk, if so why? Or have simply already detected all of them, if so how?
 
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  • #2
Because we know there's unobserved material in the halo. So it makes sense to look for them there.
 
  • #3
I only know of reasons for there being unobserved matter distributed over the galaxy, how do you know it is in the halo?
 
  • #4
Because the rotation curves are not sensitive to extra matter near the core.
 
  • #5
I never asked for why the matter is at large radii.

I just realized that maybe the disk is considered part of the Halo, and therefore any dark matter in the disk is also in the halo. So halo objects may just as well be in the disk, right?
 
  • #6
No, you asked why people are *looking* at large radii. That's the answer. Maybe they are in the disk too, maybe not.
 
  • #7
Galaxies rotate. The speed of rotation should decrease as you approach the edge. However it remains relatively constant. The most likely explanation is there is a lot of mass in a halo around the galaxy outside of the visible disc, and it's dark so we can't see it with telescopes. So this is why people are looking for MACHOs.
 
  • #8
d3mm said:
...there is a lot of mass in a halo around the galaxy outside of the visible disc...

I'm not confused about the existence of mass, but about the location. Why outside of the disk? why not in between visible Stars?
 
  • #9
That's where the equations say it must be to explain the rotation speed of the galaxy.
 

1. Why are MACHOs found in the Halo and not the disk of galaxies?

The term MACHO stands for Massive Astrophysical Compact Halo Object. These objects are believed to be made up of normal matter, such as planets, brown dwarfs, or black holes. The reason they are found in the Halo of galaxies is because the Halo is made up of dark matter, which has a much higher concentration than the disk of the galaxy. MACHOs are thought to be gravitationally bound to the dark matter in the Halo, making it more likely for them to be found there.

2. How do MACHOs affect the structure and evolution of galaxies?

MACHOs are thought to play a role in galaxy formation and evolution by interacting with dark matter in the Halo. As they move through the Halo, MACHOs can gravitationally pull on the dark matter, causing it to clump together and form structures like galaxy clusters. This process can also affect the rotation of galaxies and contribute to the overall shape and dynamics of the galaxy.

3. Can MACHOs be used to explain the missing mass problem in galaxies?

One of the main reasons scientists are interested in MACHOs is because they could potentially explain the missing mass problem in galaxies. This problem arises when the observed mass of a galaxy does not match the predicted mass based on its luminosity. MACHOs could account for some of this missing mass, but they are not thought to be the sole solution. Other theories, such as the existence of dark matter particles, are also being explored.

4. How do we detect and study MACHOs in the Halo?

MACHOs are difficult to detect and study because they do not emit light like stars and other objects in the disk of galaxies. Instead, scientists use a technique called microlensing, where the gravity of a MACHO can distort and amplify the light of a background star. This allows us to indirectly detect the presence of MACHOs in the Halo. Other methods, such as studying the motion of stars in the Halo, can also provide information about the presence of MACHOs.

5. Are there any other possible explanations for the observed microlensing events attributed to MACHOs?

While MACHOs are a leading explanation for the observed microlensing events in the Halo, there are other possible explanations. One alternative theory is the existence of primordial black holes, which could also cause the same microlensing effects. However, more research and data are needed to fully understand and distinguish between these different possibilities.

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