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Dark Matter Estimates for the Milky Way Halved

A new measurement of dark matter in the Milky Way has revealed there is half as much of the mysterious substance as previously thought.

Astrophysicist Dr Prajwal Kafle of The University of Western Australia node of the International Centre for Radio Astronomy Research probed the edge of the Milky Way, looking closely for the first time about 5 million trillion kilometres from Earth, and found that the weight of dark matter in our own galaxy is 800 billion times the mass of the Sun.

Kafle’s measurement helps to solve a mystery that has been haunting theorists for almost two decades. “The current idea of galaxy formation and evolution, called the Lambda Cold Dark Matter theory, predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don’t see that,” he said.

“When you use our measurement of the mass of the dark matter, the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see: the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy.”

University of Sydney astrophysicist Prof Geraint Lewis, who was also involved in the research, said the missing satellite problem had been “a thorn in the cosmological side for almost 15 years. Dr Kafle’s work has shown that it might not be as bad as everyone thought, although there are still problems to overcome.”

The study also allowed the scientists to measure several interesting things such as the speed required to leave the galaxy. “Be prepared to hit 550 km/s if you want to escape the gravitational clutches of our galaxy,” Kafle said. “A rocket launched from Earth needs just 11 km/s to leave its surface, which is already about 300 times faster than the maximum Australian speed limit in a car!”

The research was published in the Astrophysical Journal.