A shocking new galaxy! It lacks dark matter!

It’s a paradox. We really don’t know what dark matter is and we aren’t even completely sure whether it actually exists. Yet astrophysicists use it in their calculations and say that dark matter is intertwined with galaxies. Where there are galaxies, there is dark matter. Almost always. Because as it seems there are a few exceptions.

Source: By The Hubble Heritage Team (AURA/STScI/NASA) NASA Headquarters - Greatest Images of NASA (NASA-HQ-GRIN) [Public domain], via Wikimedia Commons

One such an exception is the galaxy NGC1052-DF2 that has been discovered by a team from the Yale University and it was completely unexpected. Dark matter may be invisible and mysterious yet it tends to be dominant in every galaxy. Experts think that galaxies are born in “lumps” of dark matter that attracts gas which then later turns into stars and later galaxies. The newly discovered galaxy somewhat contradicts the standard models of how galaxies and dark matter interact.

The research that was published by Nature uses data from the Gemini North telescopes, the W.M. Keck Observatory, Hubble telescope and many others. NGC1052-DF2 is quite big and at the same time quite dim so the scientists classify it as an ultra-diffuse galaxy. These galaxies are quite common even though we discovered them only recently in 2015. But so far we haven’t found any such galaxy that would completely lack dark matter.

Detailed analysis of the NGC1052-DF2 galaxy shows that the star clusters are orbiting much slower than they should. And the slower objects orbit in a system the lower the mass of the system. And quite unusually, in NGC1052-DF2, the mass completely matches exactly what we see – the stars. That means not much else can be in the galaxy not even dark matter.

If the researchers haven’t made a mistake it suggests that it is possible to remove the dark matter from a galaxy. But it isn’t completely clear how would that happen. But the researchers have a possible theory. NGC1052-DF2 is living among a group of galaxies ruled by a gigantic elliptic galaxy NGC 1052 found the Cetus constellation. When this elliptic galaxy was born it could have been quite the wild ride. It is possible that the NGC1052-DF2 could have lost its dark matter than even though we aren’t sure how.

Sources:

• https://www.gemini.edu/node/21048
• https://www.nature.com/articles/nature25767