Today’s “Galaxy” Stream –Dark Matter and Dinosaurs (VIEW)




If the solar system, as it orbited the center of the galaxy, were to move through the Milky Way's dark-matter disk, Lisa Randall (Warped Passages, Knocking on Heaven's Door), one of our most influential theoretical physicists, suggests that the gravitational effects from the dark matter might be enough to dislodge comets and other objects from what’s known as the Oort Cloud and send them hurtling toward Earth.

Their theory suggests that those oscillations occur approximately every 32-35 million years, a figure that is on par with evidence collected from impact craters suggesting that increases in meteor strikes occur over similar periods.

“Those objects are only weakly gravitationally bound,” said Harvard's Lisa Randall. “With enough of a trigger, it’s possible to dislodge objects from their current orbit. While some will go out of the solar system, others may come into the inner solar system, which increases the likelihood that they may hit the Earth.”

Though the exact nature of dark matter remains unknown, physicists have been able to infer its existence based on the gravitational effect it exerts on ordinary matter. Though dark matter is otherwise believed to be non-interacting, Lisa Randall and Matthew Reece, assistant professor of physics, suggested that a hypothetical type of dark matter could form a disk of material that runs through the center of the galaxy.

“We have some genuinely new ideas,” Randall said. “I’ll say from the start that we don’t know if they’re going to turn out to be right, but what’s interesting is that this opens the door to a whole class of ideas that haven’t been tested before, and potentially have a great deal of interesting impacts.”

Working with postdoctoral fellow Jakub Scholtz, Randall and Reece are also investigating whether the newly proposed form of dark matter may play a role in one of the largest mysteries in astrophysics: how the massive black holes at the centers of galaxies form.

“One possibility is that it may ‘seed’ black holes at the center of galaxies,” she said. “This is a work in progress. It’s an entirely new scenario we’re working out, so I don’t want to overstate anything, but it’s a very interesting possibility.”

Though the hypothesis adds additional complexity to a number of already-thorny questions about the nature of the universe, Randall believes it will be important to understand if a portion — even a relatively small portion — of dark matter behaves in unexpected ways.




The image at the top of the page above is composite of the dark matter disk (red contours) and the Atlas Image mosaic of the Milky Way obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology. (J. Read & O. Agertz)


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