Astronomers are puzzled as to what holds a distant galaxy together when there appears to be no dark matter present.
AGC 114905 is a galaxy about the size of the Milky Way that is about 250 million light-years away from Earth. However, there are a thousand times fewer stars in this distant galaxy than in our own.
The team, led by Pavel Mancera Pia of the University of Groningen and the Netherlands Institute for Radio Astronomy (ASTRON), didn't pick AGC 114905 by chance.
According to theoretical models, such sparse galaxies must be held together by dark matter, a mysterious invisible substance that accounts for roughly 85% of all matter in the universe. However, using the Very Large Array in New Mexico, astronomers discovered that AGC 114905 has none.
Previous observations suggested that this galaxy, along with five others, may be deficient in dark matter. However, the data were so contradictory to theory that Mancera Piña and his colleagues decided to repeat the measurements.
Despite 40 hours of measurements with one of the world's most powerful radio telescopes, the researchers discovered no dark matter.
"This is, of course, what we thought and hoped for because it confirms our previous measurements," Piña said 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."
AGC 114905 isn't the first galaxy without dark matter that astronomers have identified. In 2018, a team led by Yale University astronomer Pieter van Dokkum discovered that NGC 1052-DF2, a galaxy 60 million light-years from Earth, appeared to be dark matter-free. The scientists noted in a new statement that the methodology and measures employed in Mancera Pia's recent study are more robust than that work.
The researchers believe that another, more massive galaxy nearby may have drained their galaxy of its dark matter. Strangely, no galaxy in the region of AGC 114905 appears to be capable of accomplishing such a feat.
Meanwhile, the researchers are looking into a second ultra-diffuse dwarf galaxy from their original group of six. If they uncover no evidence of dark matter in that galaxy as well, it will strengthen the case for dark matter-poor galaxies, the scientists said in the statement.
The study was published in the journal Monthly Notices of the Royal Astronomical Society.
