Dark matter makes up about 27% of the universe and its effects influence the motion of galaxies. However, a team of NASA astronomers has discovered a galaxy without dark matter, something that did not seem possible.
Until now we believed that galaxies and dark matter went hand in hand: you can’t find one without the other. But the galaxy known as NGC1052-DF2 is almost completely devoid of this elusive matter.
“Finding a galaxy without dark matter is unexpected because this invisible and mysterious substance is the most dominant aspect of any galaxy,” said Pieter van Dokkum, leader of the study published in Nature. “For decades, we thought that galaxies began their lives as blobs of dark matter. After that, gas falls into dark matter halos, turns into stars, they slowly accumulate, and eventually galaxies like the Milky Way form. NGC1052-DF2 gives standard ideas about how we think galaxies form. “
The research collected data from the Gemini North and WM Keck Observatories, both the Maunakea Observatories, Hawaii, the Hubble Space Telescope, and other telescopes around the world.
Given its large size and faint appearance, astronomers classified NGC1052-DF2 as an ultra-diffuse galaxy, a relatively new type of galaxy that was first discovered in 2015. Ultra-diffuse galaxies are surprisingly common; however, no other galaxy of this type is devoid of dark matter.
A true rarity as a galaxy
“NGC1052-DF2 is a rarity, even among this unusual class of galaxies,” said Shany Danieli, a co-author of the work.
To look even more deeply at this unique galaxy, the team used the Gemini Multi Objective Spectrograph (GMOS) to capture detailed images of NGC1052-DF2, assess its structure, and confirm that the galaxy had no signs of interactions with other galaxies.
The results showed that dark matter is real and that it can have its own separate existence from other components of galaxies.
How was this type of galaxy formed?
“There is no theory that predicts these types of galaxies. The galaxy is a complete mystery , since everything is strange. How one of these things forms is completely unknown,” said van Dokkum.
However, the researchers do have some ideas. NGC1052-DF2 resides about 65 million light-years away in a group of galaxies dominated by the giant elliptical galaxy NGC 1052. Galaxy formation is turbulent and violent, and van Dokkum suggests that the growth of the fledgling massive galaxy thousands ago millions of years ago played a major role in the dark matter deficiency of this curious newly discovered galaxy in the universe.
Another idea is that a catastrophic event within the strange galaxy, such as the birth of thousands of massive stars, removed all gas and dark matter, halting star formation. However, these possibilities are speculative and do not explain all the characteristics of the observed galaxy. It is time to look for more examples like this to obtain more data that can help us clarify this galactic mystery.
Referencia: Pieter van Dokkum et al. “A galaxy lacking dark matter”. Nature (2018). nature.com/articles/doi:10.1038/nature25676
Image credit: NASA, ESA, and P. van Dokkum (Yale University)
Data of interest:
27% of the universe is dark matter
5% of the universe is ordinary matter
68% of the universe is dark energy
