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The Question

(Submitted April 17, 1997)

Which scientists are currently on the forefront of Milky Way study and theories? Where can I find their work?

The Answer

Boy. That is a very BIG question, because there is a tremendous amount of research involving the Milky Way galaxy, and it involves almost every aspect of theoretical and observational astronomy. Computational astrophysicists study how and why spiral structure forms and endures, and the dynamics of the globular clusters that surround the disk of the Milky Way in a halo. Observers study star forming regions, map spiral arms, measure abundances of elements in the interstellar medium, search for dark matter, etc. So, I'm just going to pick my favorite at the moment, which is the search for MAssive Compact Halo Objects (MACHOS), one possible explanation for the dark matter that must exist in galaxies, including the Milky Way. Basically, according to careful observations, we know that up to 90% of the matter in galaxies must be in the form of "dark matter" to account for the dynamics we observe. On top of that, the dark matter appears to be distributed in a spherical halo around the Milky Way, while the luminous matter is located largely in the flat disk.

The basic idea behind the MACHO project is something called "microlensing:" if a MACHO were to pass between us and a distant star, the light would be bent around the MACHO by it's gravitational field passing almost directly in front of the star (in other words, it would act as a gravitational lens). The light curve that results would be independent of the wavelength of the radiation (as opposed to many intrinsic brightness changes), would not change the polarization, would be symmetric, and would have a very distinctive shape. In searching for such microlensing events, the MACHO project is taking long baseline, large field photometric data, and analyzing each star. An early conclusion of the project was that up to 50% of the dark matter in the Milky Way may be MACHOS in the halo with masses ranging from the mass of Jupiter to one tenth the mass of the Sun. An added benefit the large collection of data on variable stars in the Large Magellanic Cloud (one target). For updates on the project, and to learn about the science team, check out: http://www.macho.mcmaster.ca/

As I said, there are many branches of study of the Milky Way. If your interest is different, I suggest reading the material in our learning centerhttp://imagine.gsfc.nasa.gov/ that relates to your interest. We also include links to other learning centers and information sources.

Regards,
Padi Boyd,
for the "Ask an Astrophysicist" Team

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