The new Hubble data explains the missing dark matter

In 2018, an international team of researchers using NASA / ESA’s Hubble Space Telescope and several other observatories discovered, for the first time, a galaxy in our cosmic neighborhood that lacks most of its dark matter.

This discovery of the galaxy NGC 1052-DF2 came as a surprise to astronomers, as it was understood that dark matter is a key constituent in current models of galaxy formation and evolution. Indeed, without the presence of dark matter, the primordial gas would not have enough gravitational pull to begin collapsing and forming new galaxies. A year later, another galaxy that lacks dark matter, NGC 1052-DF4, was discovered which further sparked intense debates among astronomers about the nature of these objects.

Now, the new Hubble data has been used to explain the reason for the lack of dark matter in NGC 1052-DF4, which resides 45 million light-years away. Mireia Montes of the University of New South Wales in Australia led an international team of astronomers to study the galaxy using deep optical imaging. They found that the missing dark matter can be explained by the effects of the disruption of the tides. The forces of gravity from the nearby massive galaxy NGC 1035 are tearing apart NGC 1052-DF4. During this process, dark matter is removed, while the stars feel the effects of interacting with another galaxy at a later stage.

Until now, the removal of dark matter in this way has remained hidden from astronomers as it can only be observed using extremely deep images that can reveal extremely faint features. “We used Hubble in two ways to find that NGC 1052-DF4 is experiencing an interaction,” Montes explained. “This includes studying the galaxy’s light and the galaxy’s distribution of globular clusters.”

Thanks to Hubble’s high resolution, astronomers were able to identify the galaxy’s population of globular clusters. The 10.4-meter Gran Telescopio Canarias (GTC) telescope and the IAC80 telescope in the Canary Islands of Spain were also used to complement the Hubble observations by further studying the data.

“It is not enough to spend a lot of time observing the object, but careful handling of the data is essential,” explained team member Raúl Infante-Sainz of the Instituto de Astrofísica de Canarias in Spain. “It was therefore important that we use not only one telescope / instrument, but several (both terrestrial and space) to conduct this research. With the high resolution of Hubble, we can identify globular clusters and then with GTC photometry we get the physical properties. “

Globular clusters are thought to form in the episodes of intense star formation that shaped galaxies. Their compact size and brightness make them easily observable and are therefore good tracers of the properties of their host galaxy. In this way, by studying and characterizing the spatial distribution of clusters in NGC 1052-DF4, astronomers can develop information on the current state of the galaxy itself. The alignment of these clusters suggests that they have been “stripped” of the host galaxy, and this supports the conclusion that a tidal outage is occurring.

By studying the galaxy’s light, the astronomers also found evidence of tidal tails, which are formed from material moving away from NGC 1052-DF4. This further supports the conclusion that this is an abort event. Further analysis concluded that the central parts of the galaxy remain intact and only about 7% of the galaxy’s stellar mass is housed in these tidal tails. This means that dark matter, which is less concentrated than stars, was previously and preferentially stripped from the galaxy, and now the outer stellar component is also starting to be stripped.

“This result is a good indicator that, while the galaxy’s dark matter has evaporated from the system, the stars are only now starting to undergo the interruption mechanism,” explained team member Ignacio Trujillo of the Instituto de Astrofísica de Canarias in Spain. “In time, NGC 1052-DF4 will be cannibalized by the great system around NGC 1035, with at least some of their stars floating free in deep space.”

The discovery of evidence supporting the tidal disruption mechanism as an explanation for the galaxy’s missing dark matter not only solved an astronomical conundrum, but also brought astronomers a sigh of relief. Without it, scientists would be faced with having to revise our understanding of the laws of gravity.

“This discovery reconciles existing knowledge of how galaxies form and evolve with the more favorable cosmological model,” Montes added.

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