Dark Matter & Galaxy Spin

The Milky Way rotates at a whopping 130 miles (210 kilometers) per second, but a new study has found that dark matter has slowed the rotation of its bar by at least 24% since its formation nearly 14 billion years ago.

"Astrophysicists have long suspected that the spinning bar at the center of our galaxy is slowing down, but we have found the first evidence of this happening," study co-author Ralph Schoenrich, an astrophysicist at University College London, said in a statement.

These new findings not only shed light on the rotation of the Milky Way but also provide an insight into the nature of one of the most elusive materials in the universe — dark matter.

The Milky Way is a barred spiral galaxy with a thick band of stars in the center and large pivoting arms stretching out across the cosmos. Scientists think that a halo of dark matter surrounds the Milky Way, extending out far beyond its visible edge, as occurs at other galaxies.

In the new study, researchers used data from Gaia, a European Space Agency mission mapping the positions of billions of stars, to study the Hercules Stream, a thick cluster of stars that revolve around the Milky Way at the same rate that the galactic bar itself spins.

Because the stars in the Hercules Stream are gravitationally trapped by the pivoting bar, slowing down the bar's rotation would cause the stars to creep outward to keep their orbits in sync with the bar's spin.

The researchers found evidence of such an outward cosmic migration when they investigated the chemical makeup of the stars. The Hercules Stream stars are rich in heavier elements, suggesting that these stars formed closer to the galactic center, where stars are about 10 times richer in metals compared to those in the galactic suburbs.  TO READ MORE, CLICK HERE...

Dark Matter

“Sterile neutrinos” are theoretically predicted new particles that offer an intriguing possibility in the quest for understanding the dark matter in our universe.

Unlike the known “active” neutrinos in the Standard Model (SM) of particle physics, these sterile neutrinos do not interact with normal matter as they move through space, making them very difficult to detect.

A team of interdisciplinary researchers, led by Lawrence Livermore National Laboratory (LLNL) and the Colorado School of Mines, has demonstrated the power of using nuclear decay in high-rate quantum sensors in the search for sterile neutrinos. The findings are the first measurements of their kind.

The research has been featured recently as a DOE Office of Science Highlight and will jump-start an extended project to look for one of the most promising candidates for dark matter, the strange unidentified material that permeates the universe and accounts for 85 percent of its total mass.

The experiment involves implanting radioactive beryllium-7 atoms into superconducting sensors developed at LLNL and has been nicknamed the “BeEST” for “Beryllium Electron-capture with Superconducting Tunnel junctions.” When the beryllium-7 decays by electron capture into lithium-7 and a neutrino, the neutrino escapes from the sensor, but the recoil energy of the lithium-7 provides a measure of the neutrino mass. 

If a heavy sterile neutrino with mass mc2 were to be generated in a faction of the decays, the lithium-7 recoil energy would be reduced and produce a measurable signal, even though the elusive neutrino itself is not detected directly.

With a measurement time of just 28 days using a single sensor, the data excludes the existence of sterile neutrinos in the mass range of 100 to 850 kiloelectronvolts down to a 0.01 percent level of mixing with the active neutrinos — better than all previous decay experiments in this range. 

In addition, simulations on LLNL supercomputers have helped the team understand some of the materials effects in the detector that need to be accounted for to gain confidence in potential sterile neutrino detection events.  TO READ MORE, CLICK HERE...