One in the eye for dark matter theorists it seems, as Phys.org reports.
In the late 1970s, astronomers Vera Rubin and Albert Bosma independently found that spiral galaxies rotate at a nearly constant speed: the velocity of stars and gas inside a galaxy does not decrease with radius, as one would expect from Newton’s laws and the distribution of visible matter, but remains approximately constant.
Such ‘flat rotation curves’ are generally attributed to invisible, dark matter surrounding galaxies and providing additional gravitational attraction.
Now a team led by Case Western Reserve University researchers has found a significant new relationship in spiral and irregular galaxies: the acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only. “If you measure the distribution of star light, you know the rotation curve, and vice versa,” said Stacy McGaugh, chair of the Department of Astronomy at Case Western Reserve and lead author of the research.
The finding is consistent among 153 spiral and irregular galaxies, ranging from giant to dwarf, those with massive central bulges or none at all. It is also consistent among those galaxies comprised of mostly stars or mostly gas.
In a paper accepted for publication by the journal Physical Review Letters and posted on the preprint website arXiv, McGaugh and co-authors Federico Lelli, an astronomy postdoctoral scholar at Case Western Reserve, and James M. Schombert, astronomy professor at the University of Oregon, argue that the relation they’ve found is tantamount to a new natural law.
An astrophysicist who reviewed the study said the findings may lead to a new understanding of internal dynamics of galaxies.
“Galaxy rotation curves have traditionally been explained via an ad hoc hypothesis: that galaxies are surrounded by dark matter,” said David Merritt, professor of physics and astronomy at the Rochester Institute of Technology, who was not involved in the research.
“The relation discovered by McGaugh et al. is a serious, and possibly fatal, challenge to this hypothesis, since it shows that rotation curves are precisely determined by the distribution of the normal matter alone. Nothing in the standard cosmological model predicts this, and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely.”