An international team of astronomers, led by Michele Cappellari from the University of Oxford, has used data gathered by the W. M. Keck Observatory in Hawaii to analyse the motions of stars in the outer parts of elliptical galaxies, in the first such survey to capture large numbers of these galaxies.
The study will be published in The Astrophysical Journal Letters.
“The surprising finding of our study was that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centres, in the same way that spiral galaxies are already known to do,” said Michele Cappellarii. “This means that in these very different types of galaxies, stars and dark matter conspire to redistribute themselves to produce this effect, with stars dominating in the inner regions of the galaxies, and a gradual shift in the outer regions to dark matter dominance.”
However, the conspiracy does not come out naturally from models of dark matter, and requires considerable tweaking or fine tuning to explain observations.
This has led to a revival by some authors of the suggestion that rather than being due to dark matter, the observed motions may be due to Newton’s law of gravity becoming progressively less accurate at large distances. It seems that even decades later, this this alternative theory still cannot be conclusively ruled out.
“This question is particularly timely in this period when physicists at CERN, after a failed first attempt, are about to restart the Large Hadron Collider to try to directly detect the same elusive dark matter particle, which makes galaxies rotate fast, if it really exists!,” said Professor Jean Brodie, principal investigator of the survey.
The study will be published in The Astrophysical Journal Letters.
“The surprising finding of our study was that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centres, in the same way that spiral galaxies are already known to do,” said Michele Cappellarii. “This means that in these very different types of galaxies, stars and dark matter conspire to redistribute themselves to produce this effect, with stars dominating in the inner regions of the galaxies, and a gradual shift in the outer regions to dark matter dominance.”
However, the conspiracy does not come out naturally from models of dark matter, and requires considerable tweaking or fine tuning to explain observations.
This has led to a revival by some authors of the suggestion that rather than being due to dark matter, the observed motions may be due to Newton’s law of gravity becoming progressively less accurate at large distances. It seems that even decades later, this this alternative theory still cannot be conclusively ruled out.
“This question is particularly timely in this period when physicists at CERN, after a failed first attempt, are about to restart the Large Hadron Collider to try to directly detect the same elusive dark matter particle, which makes galaxies rotate fast, if it really exists!,” said Professor Jean Brodie, principal investigator of the survey.