NASA’s Hubble galaxy is stripped of dark matter

Dark matter theory has long been sacrosanct in traditional astronomical circles. Astronomers rarely contradict the principle that about 85% of all matter in the cosmos is dominated by invisible matter that interacts only weakly with gravity.

Therefore, it was a surprise that its existence was questioned by recent observations by the Hubble Space Telescope of two huge galaxies that appeared to be entirely devoid of this exotic matter.

But in a document presented to The Astrophysical Journal, an international team of scientists details observations on NGC 1052-DF4, the second galaxy that was claimed to host little or no dark matter. They claim that NGC 1052-DF4, a massive galaxy about 45 million light-years away in the southern constellation of Cetus, is almost completely stripped of this strange matter via gravitational interactions with its galactic neighbor, NGC 1035.

Indeed, NASA claims that the forces pushing NGC 1035 to interfere with NGC 1052-DF4 are tearing the latter apart.

Deep optical imaging of NGC 1052-DF4 revealed that this galaxy is experiencing tidal interruptions, the authors write, caused by its interaction with its neighbor, NGC 1035. Dark matter is less concentrated than stars, and therefore during the interactions is preferably stripped from the satellites galaxies, they report.

How does this stripping actually work?

Like the friction of chalk on a blackboard, Mireia Montes, a postdoctoral fellow at the University of New South Wales in Australia and lead author of the paper, told me. As you write with chalk, the chalk particles are deposited in the direction of your script, he says.

By heart, as the galaxy continues its interaction with its huge galactic neighbor, the stripped gypsum particles would be deposited in the direction of the galaxy’s orbit, Montes says. In this case, what we can see is that the stars of NGC 1052-DF4 are actually starting to be torn from their host galaxy, he says.

This research provides case studies of how and why large galaxies actually form. Dark matter helps form galaxies as it provides a kind of gravitational well where ordinary matter can sit, cool and form stars, Montes says.

It also acts as a protective shield. Without this dark matter shield, Montes says, the galaxy would be very unstable and prone to the gravitational influence of external forces. So, he says, such galaxies would not survive in an environment where there are more massive galaxies that would engulf these galaxies stripped of dark matter.

We also know from simulations that dark matter content must decrease by about 90 percent for the interaction to start affecting the stars, he says.

These new, more accurate observations have also provided new measurements of the distance from the galaxy, NGC 1052-DF2. In 2018, a team of astronomers from Yale University reported that NGC 1052-DF2 was also devoid of dark matter. But these new observations solve that mystery.

Instead, we argue that a distance to the nearest galaxy than measured in 2018 resolves the dark matter peculiarities of the galaxy NGC 1052-DF2, Montes says. But a closer range doesn’t help in the case of NGC 1052-DF4; dark matter is still missing, he says.

And for physics as we know it to work, theorists still need dark matter.

Without the presence of dark matter, the primordial gas would not have enough gravitational pull to start collapsing and forming new galaxies, Montes says. And once a galaxy is stripped of its dark matter, Montes claims that this exotic matter ends up becoming part of the galaxy responsible for the stripping. In this case, it would be the cigar-like spiral galaxy NGC 1035.

“Over 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,” team member Ignacio Trujillo of the Instituto de Astrofísica de Canarias said in a statement. in Spain statement.