Revenge of the MACHOS

In the battle of MACHOs vs WIMPs, the dark matter debate over the last few years has definitely gone in favor of WIMPS. It is now believed that Massive Compact Halo Objects make up no more than 20% of the dark matter seen in galactic halos and possibly an even smaller percentage of the intergalactic dark matter. In the past few years, it's been tough to be a MACHO man or woman.

While the abundance estimates haven't changed, the interest in MACHOs has received a strong shot in the arm recently. In the past few years, astronomers have observed a number of gravitational microlensing events that could be black holes or brown dwarfs (the most expected types of MACHOs) in the galactic halo passing in front of distant stars, however the observations were unable to pin down distances to the lensing object as well as the mass of the object with any certainty. This gave plenty of ammunition to critics who claimed that the observed lensing objects might be dim stars in distant galaxies rather than MACHOs in the Milky Way.

Astronomers from Ohio State University using ground based telescopes as well as the Spitzer Space Telescope have reported that for the first time that they have been able to observe the speed of a lensing object. Using Hubble's law, they were able to give a 95% probability that the lensing object was really a MACHO in the Small Magellanic Cloud and was about 10 solar masses in size. What is even more interesting is that the data was good enough to show that there were actually two objects orbiting each other in a close binary - one of 7 solar masses and the other of 3 solar masses. This means that the pair was likely a binary black hole system with an orbital separation of about 5 AU.

You can read more about this from ScienceDaily.

Score one for the MACHOs!