By: Lori Adamczyk

April 26, 2000

Our universe is much more massive than simply the amount of observable matter would lead us to believe. Scientists of the past could easily account for the mass that they saw, but what about the remaining mass that they could not see but was apparently there? We can only see luminous objects directly. Modern research indicates that about 90% of the mass of the universe is dark, which means that we can’t observe it directly. This dark matter neither emits nor absorbs light and is therefore not visible to us. At least some of the dark matter in our universe is made up of baryons. Baryons are protons and neutrons, simply ordinary matter. MACHOs, or Massive Compact Halo Objects, are baryonic objects in our galaxy. Nonbaryonic objects called WIMPs (Weakly Interacting Massive Particles) may also exist. Scientists have gathered evidence that dark mater exists by observing star and galaxy motions. Further evidence was gathered and it was determined that our galaxy has a massive dark halo. Astronomers who led to the findings about the existence of dark matter include Jan Oort and Fritz Zwicky during the early 1900s, and research continues today to find out more about these phenomena.

When it was discovered that our galaxy has a massive dark halo, research began to try to determine what exactly this halo is made up of. The MACHO Project began in the late 1980’s from the ideas of Charles Alcock. A research team of scientists from all over the world got involved with the project and set up their equipment at Mt. Stromlo Observatory in Canberra, Australia. The goal of the project was to detect microlensing events caused by the dark objects and use this information to determine the make up of the massive halo. The team hypothesized that objects such as brown dwarfs and planets make up the halo. These objects amplify light from extragalactic stars, but this occurs very rarely. The team used a CCD (charge-coupled device) camera to gather the data, taking thousands of images on clear nights for several years.

Large Magellanic Cloud Mt. Stromlo Observatory

Camera used for MACHO observations

This method proved to be effective, and in 1995, enough evidence was gathered to state a conclusion about the make up of the MACHOs. The researchers found that mostly dwarf stars (white and brown dwarfs) make up the MACHOs. The results confirm the fact and provide direct evidence that MACHOs do exist and that the majority of our universe is dark.

These findings are very important in our attempts to find out exactly what our universe is made of. This data presents a very interesting result, one that will be very useful in the future as more information is discovered about dark matter. The technology used is still very new, and will be improved in the future, thus producing even more accurate results and findings. For example, as of right now, we do not know how far out the massive compact halo extends, but with improved technology and research this question may be able to be answered some day.

As one can conclude, we still have much to learn about our universe and its make up. The MACHO Project research team continues to collect data and will gain more knowledge of our universe as they continue. More will be found out about these phenomena involving dark matter and MACHOs as technology improves and research continues.