Trailing tidal tail: Stars and dust from the dwarf galaxy Sagittarius are entangled in the Milky Way.

Heidi Newberg, associate professor of physics, suggests that a “highway” of dark matter from another galaxy may be showering down on Earth. The findings may change the way astronomers look for mysterious cosmic particles, long suspected to outweigh known atomic matter.

The findings of Newberg and researchers at the University of Michigan and the University of Utah were published in the March 19 issue of Physical Review Letters.

Scientists believe that about 90 percent of the mass in the universe is made up of particles called “dark matter.” This belief is based on an unseen gravitational pull on the stars, but observations to directly detect dark matter have been sketchy. One Italy-based research group, called DAMA (for DArk MAtter), has made steady claims to have detected particles of dark matter, but so far the results have not been confirmed.

But, the disruption of a dwarf galaxy called Sagittarius, which is being torn apart and consumed by the much larger gravitational pull of the Milky Way, may be the key to reconciling the results of dark matter experiments of DAMA and other research groups.

The dwarf galaxy’s entrails of stars and dust, like a long piece of ribbon, are entangled around and within our galaxy. The so-called “trailing tidal tail” can be seen to extend from Sagittarius’ center and arcs across and below the plane of the Milky Way. The leading part of the tail extends northward above our galaxy where it then turns and appears to be showering shredded galaxy debris down directly on our solar system, Newberg and colleagues say.

“As the Milky Way consumes Sagittarius, it not only rips the stars from the smaller galaxy, but also tears away some of the dark-matter particles from that galaxy. We may be able to directly observe that in the form of a dark-matter highway streaming in one direction through the Earth,” says Newberg, who has recently identified stars near the sun that could be part of this leading tidal tail.


Originally published in Rensselaer Magazine, Summer 2004

Published June 1, 2004