Do All Galaxies Have Dark Matter?

This short article appeared in Discover’s yearly condition of science difficulty. Help our science journalism by becoming a subscriber.

Some 60 million gentle-decades from Earth — by the estimate of one particular workforce of scientists, in any case — a pair of weird galaxies is causing a cosmic stir. The strange galaxies, named NGC 1052-DF2 and NGC 1052-DF4 (or DF2 and DF4, for short), are the initial recognized galaxies born without any considerable total of dark make a difference. If verified, their existence would throw a wrench into our knowledge of how galaxies sort and evolve. But, as Carl Sagan appreciated to say, remarkable promises have to have remarkable proof. And, in accordance to some scientists, the proof for these dark-make a difference-deficient galaxies does not maintain up.

The Declare: Absolutely nothing to See Below

Astrophysicist Pieter van Dokkum of Yale University was definitely surprised when he initial spotted DF2. Right after data from the Dragonfly Telephoto Array, the Sloan Digital Sky Survey, the Hubble Room Telescope and Keck Telescope were analyzed, the implications were obvious: DF2 is not entire of dark make a difference like other galaxies.

“This point is astonishing,” states van Dokkum, “a gigantic blob that you can appear by. It is so sparse that you see all of the galaxies guiding it. It is practically a see-by galaxy.”

The astronomers appeared to the pace of DF2’s globular clusters (big teams of aged stars) to estimate how substantially mass the galaxy holds. When they in contrast their mass estimate to how substantially make a difference was visible, the two were a close match, suggesting the galaxy is only composed of visible make a difference.

This calculation relies upon on an correct evaluation of the length to the galaxy, nevertheless. Addressing criticisms about their estimate, van Dokkum’s team up to date their DF2 length to about sixty one million gentle-decades — marginally nearer to Earth, but nevertheless in just the variety in which it would have negligible dark make a difference.

The team went on to find a second, very similar galaxy, DF4, which furthermore has an obvious dearth of dark make a difference. “I imagine this is definitive,” states van Dokkum. “The [data] are unable to be argued with: It is caused by very well-comprehended stellar physics, and [is] as immediate as length indicators get.”


A computer simulation exhibits the evolution of dark make a difference in the universe. But is it component of each and every galaxy? (Credit history: Millennium-II Simulation)

The Counterpoint: You have Obtained It All Wrong

Ignacio Trujillo of the Instituto de Astrofísica de Canarias agrees that if DF2 were 60 million to sixty five million gentle-decades absent, as van Dokkum suspects, then it would be a strong prospect for the initial case in point of a galaxy born without dark make a difference. But if DF2 is nearer, the galaxy’s noticed qualities would slide in line with your normal dark-make a difference-dominated galaxy.

Trujillo and his workforce set out to independently figure out the length to DF2. They recurring van Dokkum’s group’s measurements and included an examination of the luminosities of pink big stars in just it. Having that data collectively, the workforce concluded DF2 is very likely only about 42 million gentle-decades absent, whilst DF4 is only about 46 million gentle-decades absent. This suggests the two galaxies harbor as substantially dark make a difference as you would expect from average, run-of-the-mill galaxies.

“All in all,” Trujillo’s workforce concluded in their reaction paper, “the proposition that equally NGC 1052-DF2 and NGC 1052-DF4 are ‘missing dark matter’ is nevertheless much from remaining positioned on guaranteed footing.”

dark matter star clusters

(Credit history: Roen Kelly/Explore)