Mysteries of Dark Matter: Unraveling the Enigma Behind a Star Stream Disruption

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A confusing “break” in a star stream surrounding the Milky Way may be attributed to dark matter — if it turns out this elusive cosmic entity interacts with itself.

The feature in question manifests in the GD-1 stellar stream, a slender assembly of stars traveling together along a common path through the Milky Way’s expansive halo. The GD-1 stellar stream has been extensively examined by astronomers, but a void in its formation has remained a mystery.

Now, researchers from the University of California, Riverside, suggest that this anomaly could stem from a sub-halo of self-interacting dark matter contained within the larger halo of dark matter surrounding our galaxy.

“This research paves a promising new path for exploring the self-interacting characteristics of dark matter through stellar streams,” stated team leader and University of California, Riverside researcher Hai-Bo Yu in a statement. “It represents an exciting advancement in our comprehension of dark matter and the dynamics of the Milky Way.”

Becoming warmer

Researchers are eager to unravel the dark matter enigma since this phenomenon constitutes the vast bulk of the “material” in the universe — approximately 85%, in fact. This implies that everything we observe around us, such as stars, planets, moons, you, me, and virtually everything else, comprises just 15% of the universe’s matter.

Researchers are aware that dark matter is not composed of atoms made up of protons, neutrons, and electrons because it does not engage with light or regular matter.

However, a critical question for scientists remains: Does dark matter interact with itself?

Regrettably, the fact that dark matter does not engage with light similarly renders it virtually undetectable. Thus, this inquiry is quite challenging to explore.

Nonetheless, if dark

Dark matter refrains from interacting with regular matter, and stars are certainly made of ordinary matter, so you might be curious about how this enigmatic substance could lead to a disruption in a stellar stream.

The essential point here is that dark matter does engage with gravity. Given that gravity emerges from the bending of the very structure of space (thanks to Albert Einstein) and both ordinary matter and light also move through space, it implies that, while these more familiar components of the universe can overlook dark matter, they cannot disregard its gravitational impacts.

Moreover, researchers have analyzed the disturbance in the GD-1 stellar stream and concluded that the gravitational effects of known globular clusters or the recognized satellite galaxies of the Milky Way couldn’t have instigated it.

If concentrated dark matter resides in a sub-halo within the broader halo of the Milky Way, then the gravitational fluctuations it induces could have disturbed this stellar stream.

Nonetheless, for this to occur, the dark matter present in this sub-halo must be denser than the dark matter proposed in our most accurate model of the universe’s evolution: the Lambda Cold Dark Matter (LCDM) framework.

“Cold dark matter sub-halos generally lack the required density to generate the unique characteristics observed in the GD-1 stream,” Yu clarified.

In this context, “cold” refers to dark matter that moves slowly relative to the speed of light and does not interact with itself. The opposite would be “hot,” or self-interacting, dark matter.

A possible outcome of self-interacting dark matter pertains to its ability to collapse under its own gravitational force and increase in density.

Yu and colleagues simulated the ramifications of this collapsing dark matter sub-halo on the disruption seen in the GD-1 stellar stream.

“However, our study illustrates that a collapsing self-interacting dark matter sub-halo could reach the required density,” Yu added. “Such a compact sub-halo would be sufficiently dense to exert the gravitational effect necessary to explain the observed disturbances in the GD-1 stream.”

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— Something ‘unusual’ is happening with the Milky Way’s dark matter halo

— Could dark matter have been created in a ‘Dark Big Bang?’

— Dark matter might exist in a dense mist surrounding stellar remnants

“Our team’s discoveries provide a fresh explanation for the observed spur and gap characteristics in GD-1, which have long been believed to signify a close encounter with a dense entity,” Yu remarked. “In our hypothesis, the ‘perturber’ is the self-interacting dark matter sub-halo, which alters the spatial and velocity distributions of the stars in the stream and produces the unique features visible in the GD-1 stellar stream.”

Naturally, this might indicate that the LCDM model isn’t the most suitable paradigm for the universe after all.

Should this be the case, hot dark matter indicators like the disruption in the GD-1 stellar stream could provide scientists a means to examine dark matter’s attributes.

The research conducted by the team was published on Jan. 3 in the Astrophysical Journal Letters.