Maine Perspective Front Page
Cutting Edge
University of Maine Research on the Frontiers of Science
Galactic Halos
Researchers at the University of Maine and Cornell University have recently simulated a process that sheds light on the nature of the dark matter in galactic halos.
Using computer simulations, Thomas Zeltwanger and Neil Comins at UMaine, and Richard Lovelace at Cornell University, have reproduced the shapes and various details of off-center spiral galaxies created when galaxies rapidly pass each other. The motions of the stars and gas in their model support the belief that lopsided spiral galaxies are sloshing in halos of dark matter.
By studying the behavior of such galaxies, researchers hope to help determine the nature of these as-yet-unseen galactic halos.
The results of this research were presented earlier this month to the American Astronomical Society in Atlanta.
Lopsided spiral galaxies have spiral arms and interstellar gas and dust that are not distributed uniformly around the bright center, or nuclear bulge, of the galaxy. Galactic halos are distributions of dark matter in which galaxies are embedded. Observations reveal that up to 90 percent of a typical galaxy's mass is in its halo. Astronomers infer the existence of halos by their observed gravitational effects on visible matter, but the nature of the halo matter is still under investigation.
Observations reveal that a third of all spiral galaxies may have lopsided spiral structures. Such galaxies include M 31, located 2.9 million light years away in the constellation Andromeda: M 33; 3.0 million light years away in the constellation Triangulum; M 101, located 27 million light years away in the Ursa Major; NGC 4486B, located 50 million light years away in the constellation Virgo; and K64, located 200 million light years away in the constellation Andromeda, among many others.
The simulations give strong evidence that when the visible stars, gas and dust in the disk respond to a passing galaxy more readily than does the dark matter, the spiral galaxy's visible matter is pulled off-center, creating lopsided galaxies. Dark matter that is relatively hot moves rapidly and responds relatively little to the gravitational tug of a passing galaxy.
Since stars and cool gas in a galaxy respond more strongly than the halo, these latter elements are pulled slightly away from the halo as the other galaxy passes. Simulations reveal that as the galaxies move away from each other, stars and cool gas swirl back to the halo's center. Had the dark matter all been of the proposed cool variety, then the halo would be shifted by the other galaxy's gravity as much as the visible stars and gas. In that case, the observed sloshing of stars and gas does not occur. Results of the simulations suggest that at least some of the dark halo matter in disk galaxies is of the proposed hot, rapidly moving variety. This result needs to be verified by further simulations and observations.
These simulations also suggest that this spiraling process can create knots of gas and stars, such as those seen in the galaxy M83, located 15 million light years away in the constellation Hydra. The overall motion of the stars and gas swirling back into the halo center also appears to help maintain the galaxy's spiral structure, which otherwise washes out into a more uniform disk.
By determining the time since an encounter between galaxies, scientists may be able to determine the distribution of halo matter from the lopsided appearance of the spiral galaxy. The researchers have also discovered that central bars of stars, found in many spiral galaxies, can be suppressed by the swirling motion of the stars and gas moving back into place in the halo.
However, they find that the presence of massive black holes, which have been observed in a growing number of galaxies, including our own Milky Way, can actually cause the formation of a bar where one wouldn't exist. By understanding the composition and dynamics of galaxies, astronomers hope to be able to infer more information about their as-yet unseen components.
Cross-Pollination Study
The chance of cross-pollination between corn plants in the field, whether produced by traditional breeding practices or by genetic engineering, is small for plants in close proximity to each other and quickly drops to zero with increasing distance, according to a recent UMaine study.
The study was conducted by John Jemison, an agronomist and water quality specialist with Cooperative Extension, and Michael Vayda, professor in the Department of Biochemistry, Microbiology and Molecular Biology.
Two corn varieties, including genetically modified (GM) Roundup Ready corn, were grown at the University's Rogers Farm. Some of the GM corn was cut down by vandals last August after plants had finished shedding their pollen. Offspring (seeds) from the non-genetically modified corn were grown in the Roger Clapp Greenhouse to determine if any cross-pollination had occurred between the Roundup Ready corn and the non-GM corn.
Results of the study indicate that, in hybrid corn grown downwind from the Roundup Ready plots, there was about 1 percent cross-pollination in the first six rows within 100 feet of the Roundup Ready corn. In the middle six rows, the frequency dropped to 0.1 percent, and in the last six rows the frequency dropped to 0.03 percent. No cross-pollination was found in corn 1,000 feet away.
Only plants immediately downwind of the Roundup Ready corn exhibited significant cross pollination.
The results of the study indicate that a 1,000-foot buffer or border rows adequately protect organic corn crops from neighboring crops of genetically modified varieties, says Jemison.