The mystery surrounding galaxy NGC 1052-DF2 is deepening with every new revelation as astronomers gaze at it using the Hubble Space Telescope. When astronomers first observed this oddball galaxy, they could not believe that it lacked the primary source of material to hold it — Dark matter.
The paper published in the June volume of The Astrophysical Journal Letters is based on 40 orbits of NASA’s Hubble Space Telescope that showed that the galaxy is lacking dark matter. The new observations have deepened the mystery around the “see-through” galaxy, which is almost as wide as the Milky Way but contains only 1/200th of the number of stars as our galaxy.
Dark matter is the invisible glue that makes up the bulk of the universe’s matter. It is yet to be observed, but have been hypothesised for decades. Observed by the motions of the stars, this material makes up to 80 per cent of the universe and several astronomical calculations have confirmed its existence, kicking off worldwide research to observe them directly.
Scientists observed images captured by the Hubble and found that the ancient stars within the galaxy are so spread out that even distant galaxies could also be seen through it. They observed the motions of the stars within the galaxy, their velocities of which depend upon the gravitational pull. They targeted ageing red giant stars on the outskirts of the galaxy to calculate vast intergalactic distances by studying their brightness.
The measurement of the distance between Earth and the DF2 galaxy is critical to estimate the amount of its dark matter. Astronomers observed that the galaxy was much farther away than their initial estimates. The new estimates put it at 72 million light-years as opposed to 42 million light-years proposed earlier.
“For almost every galaxy we look at, we say that we can’t see most of the mass because it’s dark matter. What you see is only the tip of the iceberg with Hubble. But in this case, what you see is what you get. Hubble really shows the entire thing. That’s it. It’s not just the tip of the iceberg, it’s the whole iceberg,” Pieter van Dokkum of Yale University said.
DF2 is not the only galaxy in the universe lacking dark matter. Another ghostly galaxy NGC 1052-DF4 or DF4 lacks the material too. The DF4 was studied by Hubble in 2020 to obtain its accurate distance from Earth. Scientists, however, suggest that DF4’s dark matter may have been stripped due to tidal forces from another galaxy. Researchers now think that both DF2 and DF 4 were members of a collection of galaxies and drifted away from the group.
DF4 is 6.5 million light-years away from DF2.
Researchers are now looking for more such galaxy in the vastness of the universe to understand why some galaxies lack the critical dark matter and if they do how are they holding together.