Mystery of Galaxy Thought to be Devoid of Dark Matter Resolved

Image: NASA/Hubble Space Telescope

Dark matter is the most abundant physical substance in the universe, occurring five to six times more than the ordinary matter we are made of. On smaller scales, dark matter is thought to play a critical role in the formation of galaxies. Last year, however, our current understanding of galactic formation was jeopardized by the discovery of NGC1052-DF2, a galaxy which appeared to be completely devoid of dark matter.

Due to the puzzling nature of NGC1052-DF2, a group of researchers led by the Instituto de Astrofísica de Canarias re-examined all the data associated with the original study. The conclusion that the galaxy had no dark matter was based on the measurement of the distance to the galaxy. This distance had been previously determined in another study to be around 20 megaparsecs, or approximately 65 million light years away. The team then used multiple independent measurement methods, and carefully determined the distance to NGC1052-DF2. They determined that in reality, this galaxy is 13 megaparsecs away, only 65% the previously measured distance.

This anomaly implied that the previously determined measurement of the galaxy’s mass was also incorrect, with the galaxy’s true mass being half of what it was thought to be. From this, they were able to ascertain that the mass of the stars within the galaxy is around 25% of the believed value. Using this result, the team finally concluded that NGC1052-DF2 does have dark matter after all; in fact, the galaxy’s mass seems to be around 75% dark matter. These revised measurements allowed the team to show that there is “plenty of room for dark matter” in this galaxy.

The dark matter-free galaxy mystery has not been resolved yet. The same group of researchers who wrote the original paper on NGC1052-DF2 wrote another paper a different galaxy, NGC1052-DF4, where dark matter is also seemingly absent. The researchers led by the Instituto de Astrofísica de Canarias are conducting a study on the distance to NGC1052-DF4, and it appears that it may also have been measured to be farther away than it is. It appears this mystery should soon be put to rest once and for all.

Read the original research paper here:

https://academic.oup.com/mnras/article-abstract/486/1/1192/5380810?redirectedFrom=fulltext