Вадим Дудченко
Администратор портала

Astronomers from the Netherlands, the United Kingdom and the United States have found no trace of dark matter in AGC 114905, a gas-rich ultra-diffuse galaxy approximately 248 million light-years from Earth.

This image shows the gas-rich ultra-diffuse galaxy AGC 114905; the stellar emission is shown in blue; the green clouds show the neutral hydrogen gas. Image credit: Javier Román / Pavel Mancera Piña.

AGC 114905 is located about 76 megaparsecs (248 million light-years) away in the constellation of Pisces.

It is classified as an ultra-diffuse dwarf galaxy, with the name ‘dwarf galaxy’ referring to its luminosity and not to its size.

AGC 114905 is about the size of our own Milky Way Galaxy but contains a thousand times fewer stars.

The prevailing idea is that all galaxies, and certainly ultra-diffuse dwarf galaxies, can only exist if they are held together by dark matter.

“When we discovered six galaxies with little to no dark matter, we were told ‘measure again, you’ll see that there will be dark matter around your galaxy’,” said Dr. Pavel Mancera Piña, an astronomer at the University of Groningen and ASTRON.

“However, after fourty hours of detailed observations, the evidence for a dark matter-free galaxy only became stronger.”

The researchers collected data on the rotation of hydrogen in AGC 114905 between July and October 2020 using the Karl G. Jansky Very Large Array.

Subsequently, they made a graph showing the distance of the gas from the center of the galaxy on the X-axis and the rotation speed of the gas on the Y-axis. This is a standard way to reveal the presence of dark matter.

The graph shows that the motions of the gas in AGC 114905 can be completely explained by just normal matter.

“This is, of course, what we thought and hoped for because it confirms our previous measurements,” Dr. Mancera Piña said.

“But now the problem remains that the theory predicts that there must be dark matter in AGC 114905, but our observations say there isn’t. In fact, the difference between theory and observation is only getting bigger.”

In their paper, the authors list the possible explanations for the lack of dark matter one by one.

“For example, AGC 114905 could have been stripped of dark matter by large nearby galaxies,” they said.

“But there are none. And in the most reputed galaxy formation framework, the so-called cold dark matter model, we would have to introduce extreme parameter values that are far beyond the usual range.”

“Also with modified Newtonian dynamics, an alternative theory to cold dark matter, we cannot reproduce the motions of the gas within the galaxy.”

There is one more assumption that could change the conclusions. That is the estimated angle at which they think the team is observing the galaxy.

“But that angle has to deviate very much from our estimate before there is room for dark matter again,” said Dr. Tom Oosterloo, an astronomer at ASTRON.

The team’s paper will be published in the Monthly Notices of the Royal Astronomical Society.


Pavel E. Mancera Piña et al. No need for dark matter: resolved kinematics of the ultra-diffuse galaxy AGC 114905. MNRAS, in press; arXiv: 2112.00017


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