Dark matter is more valuable than gold

Wobbly galaxies help shine a light on the universe’s strangest stuff.

Dark matter, widely known as the universe’s most mysterious stuff, is rarer on Earth than gold, and that’s despite the fact that dark matter outweighs “ordinary matter” by a staggering ratio of five to one.

The finding came courtesy of scientists who propose a novel way to map dark matter using the “wobble” of the Milky Way. That wobble is due to the influence of the Milky Way’s satellite galaxies, like the Large Magellanic Cloud (LMC), and rapidly rotating neutron stars, or “pulsars.” Fascinatingly, pulsars act like “cosmic lighthouses” in the cosmos, sweeping beams of light across vast distances, reported Space.com.

The team’s previous work has in fact used these extreme stars, when orbited by stellar companions in systems called “binary pulsars,” as dark matter probes. The scientists’ new research, however, further suggests solitary pulsars could be used in such an investigation, too.

“When we first began this work in 2021 and did the follow-up publication last year, our sample was composed of pairs of millisecond pulsars, binary millisecond pulsars,” Sukanya Chakrabarti of the University of Alabama in Huntsville (UAH) said in a statement. “However, most pulsars are not in pairs. Most of them are solitary. In this new work, we show how to effectively double the number of pulsars we can use to constrain dark matter in the galaxy by rigorously using solitary pulsars to measure galactic accelerations,” reported Space.com.

By “constraining dark matter,” Chakrabarti means limiting the possible properties and characteristics of dark matter.

As more neutron star data is collected, the gravitational acceleration measurement of binary pulsars and their single counterparts could shine a light on the gravitational field of the Milky Way and, thus, the shape and distribution of dark matter in our galaxy, reported Space.com.

“Because it’s a larger sample, we now have a breakthrough,” Chakrabarti said. “We are able to measure the local dark matter density using direct acceleration measurements for the first time.”

That tells researchers that dark matter can’t be made of atoms like everyday matter is, because the particles that comprise atoms, electrons, protons, and neutrons, do interact with light.

The only way we can know whether dark matter exists at all is via its interaction with gravity and the influence this interaction has on light and everyday matter. In fact, this influence is crucial, reported Space.com.

If galaxies weren’t packed with invisible dark matter, the gravitational influence of their “everyday matter”, -stars, planets, dust clouds, and so on-, would not be sufficient to prevent them from flying apart as they spin.

Galactic dark matter content is thought to be heavily concentrated in the centers of galaxies, but it’s believed the substance also extends out to form a spherical shell that extends far beyond the limits of a galaxy’s visible matter.

That explains how dark matter can be less common in an average sphere around the size of Earth than gold is here on our planet, but still vastly outnumber atoms of all types. Space is vast, and dark matter is way more spread out across the universe than gold or other elements are, reported Space.com.

The team found that there is less than 2.2 pounds (1 kilogram) of dark matter in a volume equivalent to that of the entire Earth. “If you compare that to millions of kilograms of gold produced every year, you can see that pound-for-pound, dark matter is more valuable than gold!” Chakrabarti said.

Dark matter, which makes up about 85% of the total matter in the universe, has been sort of a problematic phenomenon for scientists because it doesn’t interact with light, or, if it does, that interaction is too weak to be detected with current technology, reported Space.com.

That tells researchers that dark matter can’t be made of atoms like everyday matter is, because the particles that comprise atoms, –electrons, protons, and neutrons-, do interact with light.

The only way we can know whether dark matter exists at all is via its interaction with gravity and the influence this interaction has on light and everyday matter. In fact, this influence is crucial, reported Space.com.

If galaxies weren’t packed with invisible dark matter, the gravitational influence of their “everyday matter”, -stars, planets, dust clouds, and so on-, would not be sufficient to prevent them from flying apart as they spin.
Galactic dark matter content is thought to be heavily concentrated in the centers of galaxies, but it’s believed the substance also extends out to form a spherical shell that extends far beyond the limits of a galaxy’s visible matter, reported Space.com.
That explains how dark matter can be less common in an average sphere around the size of Earth than gold is here on our planet, but still vastly outnumber atoms of all types. Space is vast, and dark matter is way more spread out across the universe than gold or other elements are.

Chakrabarti explained that in her earlier work, she used computer simulations to show that, as the Milky Way interacts with its satellite galaxies, the stars in our galaxy feel a very different tug from gravity depending on whether the stars are located above or below what is known as the “galactic disk,” reported Space.com.

The LMC is one of the Milky Way’s larger dwarf galactic satellites, for instance. As it orbits our own galaxy and passes near to the Milky Way, it can pull some of the mass in the Milky Way’s galactic disk towards it, leading to a lopsided galaxy with more mass on one side. As a result, Chakrabarti said that gravity is felt more strongly on one side of the Milky Way.

“It’s almost like the galaxy is wobbling, kind of like the way a toddler walks, not entirely balanced yet,” she continued. “So this asymmetry or disproportionate effect in the pulsar accelerations that arises from the pull of the LMC is something that we were expecting to see. Here, with the larger sample of pulsar accelerations, we are actually able to measure this effect for the first time,” said Chakrabarti, as reported by Space.com.

All Credit To: Space.com