1. The MACHO Experiment Aishwarya Bhake Astronomy 007: Big Bang and Beyond 4/13/2006

2. What is a MACHO?  Massive Compact Halo Object Any object such as a white dwarf, neutron star, or black hole that could account for some or all of the dark matter in the halos of galaxies Generally a small chunk of baryonic matter which emits little or no radiation and drifts through interstellar space unassociated with any solar system

3. Observing MACHOs  Gravitational lensing is capable of detecting compact objects in the halo of the Milky Way Galaxy However, the smaller the mass, the smaller the bending of the light Still, a compact object can still bend light in a predictable manner

5. Microlensing  If a compact object were to pass in front of a background star, it would split the image into multiple images  These multiples images can be resolved together The net result would be a temporary brightening of the background star Method used by the MACHO Experiment

6. The MACHO Experiment  Led by Charles Alcock  Began in 1992  Use a 1.27-meter telescope at Mount Stromlo Observatory, Australia  a dichroic beamsplitter filters provide simultaneous images in two passbands, a red band (approx. 5900-7800 Å) and a blue band (approx. 4500-5900 Å).  Two large CCD cameras cover 0.5 square degrees of the sky  Primary aim: test the hypothesis that a significant fraction of the dark matter in the halo of the Milky Way is made up of objects like brown dwarfs or planets

7. The MACHO Experiment  These objects can be identified because of the amplification of the light from extragalactic stars by the gravitational lens effect. The amplification can be large, but events are extremely rare: it is necessary to monitor photometrically several million stars for a period of years in order to obtain a useful detection rate.  Photographing stars in the Large Magellanic Cloud  As of January 1993, 1.7 million stars had been analyzed  Preliminary time-series analysis has been performed to find variable stars and possible MACHO events

8. Large Magellanic Cloud

9. Mount Stromlo Observatory

10. Conclusion  “Our conclusion from this preliminary analysis is that while we have not analyzed enough data to put a statistically significant limit of the abundance of MACHOs in the Halo of our galaxy, this analysis has clearly demonstrated that the background of variable stars mimicing microlensing events is at worst comparible to our expected signal.” - The First Data from the MACHO Experiment

11. http://www.eg.bucknell.edu/physics/astronomy/as102- spr00/web_pages/jessica.html http://web.mit.edu/~redingtn/www/netadv/specr/78/node3.html http://arxiv.org/PS_cache/astro-ph/pdf/9304/9304014.pdf http://wwwmacho.anu.edu.au/ Hawley, John F. and Katherine A. Holcomb. Foundations of Modern Cosmology. New York: Oxford University Press. 1998.