MACHOs

Massive Compact Halo Objects, or MACHOs, could be one of the missing pieces of the puzzle that astronomers call dark matter. These objects, as the name suggests, are found in the halo of the galaxy and could help explain why some bodies in the halo orbit faster than the amount of light would tell us.




MACHOs are normal baryonic matter, i.e. they are made up of baryons*

• Baryons are subatomic particles made up of quarks. Well-known examples would be protons and neutrons. Baryonic matter is matter made up of ordinary atoms.

Non-baryonic matter would be something like free electrons and other leptons (which I will not get into here) or neutrinos (which we be discussed in a future post).


So what are MACHOs? A few ideas exist of what they could be. They include, but are not limited to, the following:

• White dwarfs, especially older white dwarfs. After a white dwarf is no longer hot, it will cool down and be called a black dwarf since it no longer is radiating energy. They are thought to exist, but we have never found one...yet.
• Neutron stars that have had their supernova remnants dissipate or are not pulsars.
• Solar mass black holes
• Brown dwarfs which form the same way a star does, but cannot sustain fusion in its core. There will be more on these in a later post.
• Planets. Again, this will be discussed in a future post.

We know that MACHOs are not the only explanation for dark matter as they are only found in the halo of the galaxy. We know from the mass curve of the galaxy that dark matter is found within the disk as well. The five above objects can also be found in the disk as well.