The puzzle of the strange galaxy made up of 99.9% dark matter is solved

Image and amplification (in color) of the ultra-diffuse Galaxy Dragonfly 44 with the Hubble Space Telescope. Credits: Temur Saifullahi and NASA / HST.

Currently, the formation of galaxies is difficult to understand without the presence of a ubiquitous, but mysterious component, called dark matter. Astronomers have measurements of how deep matter is around galaxies, and they have found that this view varies between 10 and 300 times the amount of matter. However, a few years ago, the discovery of a very diffuse object named Dragonfl44 changed the scene. It was found that this galaxy contains 10,000 times more dark matter than the stars. Back from this discovery, astronomers have made efforts to see if this object is indeed odd, or whether something went wrong with the analysis of the observations. Now we have the answer.

An international team led by the Kapatin Institute of the University of Groningen (Netherlands), with participation by the Instituto de Astrophysica de Canarias (IAC) and the University of La Laguna (ULL), has found that the total number of spherical groups around the dragonfly is 44 and therefore, Dark matter content is much lower than earlier findings, suggesting that this galaxy is neither unique nor anomalous. The result was recently published Monthly notice of the Royal Astronomical Society (MNRAS).

The galaxy Dragonfigure 44 was detected in an in-depth survey of the coma cluster, a group consisting of several thousand galaxies. From the beginning, the galaxy was considered remarkable by researchers because the amount of dark matter they estimated was equivalent to about one billion solar masses in the Milky Way.

However, instead of including about a million stars as the Milky Way, the DF44 has only one hundred million stars, a thousand times less. This means that the amount of dark matter was ten thousand times greater than its stars. If this were true, it would have been a unique object, containing about 100 times more dark matter than was expected from its number of stars.

Nevertheless, from a thorough analysis of the system of spherical clusters around Dragonfly 44, researchers have discovered that the total number of spherical clusters is only 20, and the total amount of dark matter is about 300 times that of luminous matter, which means That this is not a way out of the normal value for galaxies of this type.

“The fact that in our work we found only 20 spherical clusters, compared to 80 previously claimed, greatly reduces the amount of darker matter that is believed to be included in the galaxy,” Igasio Trujillo , An IAC researcher and co-author of the article. “Also, with the number of spherical clusters, we found that the amount of Dark Matter in Dragonfly 44 is similar to what is expected for galaxies of this type. The ratio of visible to dark matter is not 1 in 10,000, but out of 300. There is one., “Trujillo says.

“Dragonfly 44 has been a discrepancy all these years that could not be explained with the current galaxy formation model. We now know that the previous results were inaccurate and that the DF44 is not exceptional. It’s time to move on,” Tyme Saifullahi telling. , Researcher at the CapeTeen Institute and the first author of the article.

Another IAC researcher, Michael A. Beasley, an expert on globular clusters and a co – says, “Our work shows that this galaxy is not so eccentric nor unpredictable. In this way the model of galaxy formation needs modification. Without explaining it. ” Author of the article.

The total number of spherical clusters is related to the total mass of a galaxy. So, if the number of spherical groups is measured, the amount of dark matter can be found, especially if the amount of visible matter is a small fraction of the total.

“However, we do not have a physical description for the relationship between the total spherical clusters and the total mass of the galaxy. This is purely observational knowledge. This may have to do with its original gas volume. Stars, and spherical clusters have formed themselves. The darker the material in a galaxy, the more gas, “said Johan H., an IAC researcher. Nappan and the article’s co-authors also state.

The dark side of the spreading galaxies

more information:
Temur Saifullahi et al, The number of spherical clusters around the iconic UDG DF44 is expected for dwarf galaxies, Monthly notice of the Royal Astronomical Society (2020). DOI: 10.1093 / mnras / staa3016

Provided by Instituto de Astrophysica de Canaria

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