A team of astronomers have studied a distant galaxy and found evidence that it contains little, if any, dark matter, according to a paper published this month in Monthly Notices of the Royal Astronomical Society. The confusion is that scientists didn't previously think that would be possible.
The galaxy, AGC 114905, is about 250 million light-years away and around the size of the Milky Way. It’s also much more diffuse than the Milky Way, containing about a thousand times fewer stars. According to theoretical models, gas-rich ultra-diffuse galaxies like AGC 114905 should be held together by dark matter, an unseen type of matter that’s thought to make up most of the universe.
Pavel Mancera Piña and his co-authors previously observed AGC 114905 and five other ultra-diffuse galaxies, finding little indication of dark matter among them. After those findings were published, Mancera Piña’s team then took measurements of AGC 114905, the most extreme of the six galaxies, for 40 hours with the Very Large Array, an observatory that allows for higher resolution data. They found that the movement of the galaxy’s gasses can be explained by regular matter, without the need for dark matter.
"This is, of course, what we thought and hoped for because it confirms our previous measurements," said Mancera Piña in a statement. "But now the problem remains that the theory predicts that there must be dark matter in AGC 114905, but our observations say there isn't. In fact, the difference between theory and observation is only getting bigger."
There’s been some debate in recent years about the existence of other ultra-diffuse galaxies that seem to have little or no dark matter. Other researchers have also studied galaxies that are apparently dark matter deficient, but AGC 114905 is much more isolated, and Mancera Piña’s team say their techniques and measurements are more robust. The team says errors that would disrupt their findings, like miscalculating the angle of the galaxy, are unlikely.
Astronomers aren’t sure yet how dark matter-free galaxies could form, but further study of galaxies like AGC 114905 might help them understand more about the nature of dark matter.
Kait Sanchez is a freelance writer for IGN. Find them on Twitter @crisp_red.
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The galaxy, AGC 114905, is about 250 million light-years away and around the size of the Milky Way. It’s also much more diffuse than the Milky Way, containing about a thousand times fewer stars. According to theoretical models, gas-rich ultra-diffuse galaxies like AGC 114905 should be held together by dark matter, an unseen type of matter that’s thought to make up most of the universe.
Pavel Mancera Piña and his co-authors previously observed AGC 114905 and five other ultra-diffuse galaxies, finding little indication of dark matter among them. After those findings were published, Mancera Piña’s team then took measurements of AGC 114905, the most extreme of the six galaxies, for 40 hours with the Very Large Array, an observatory that allows for higher resolution data. They found that the movement of the galaxy’s gasses can be explained by regular matter, without the need for dark matter.
"This is, of course, what we thought and hoped for because it confirms our previous measurements," said Mancera Piña in a statement. "But now the problem remains that the theory predicts that there must be dark matter in AGC 114905, but our observations say there isn't. In fact, the difference between theory and observation is only getting bigger."
There’s been some debate in recent years about the existence of other ultra-diffuse galaxies that seem to have little or no dark matter. Other researchers have also studied galaxies that are apparently dark matter deficient, but AGC 114905 is much more isolated, and Mancera Piña’s team say their techniques and measurements are more robust. The team says errors that would disrupt their findings, like miscalculating the angle of the galaxy, are unlikely.
Astronomers aren’t sure yet how dark matter-free galaxies could form, but further study of galaxies like AGC 114905 might help them understand more about the nature of dark matter.
Kait Sanchez is a freelance writer for IGN. Find them on Twitter @crisp_red.
Continue reading...