Gravitational-wave researchers increasingly think that globular clusters, dazzling, celestial “snow globes” –among the oldest objects in the Universe– populated with hundreds of thousands of densely packed stars, harbor dark “hearts” loaded with dozens to even hundreds of black holes–by far the greatest concentration of these exotic objects found anywhere in the universe. Gravitational-wave observations of binary black hole and neutron star mergers by LIGO and Virgo in the past five years have opened a completely new new way of observing the Universe.
From our tiny blue dot, the universe appears inconceivably vast. In the grand cosmic scheme of things, all the light in the observable universe provides about as much illumination as a 60-watt bulb seen from 2.5 miles away, says Marco Ajello, an astrophysicist at Clemson University, who led a team in 2018 that has measured all of the starlight ever produced throughout the history of the observable universe.
“It’s mind-boggling to actually witness material orbiting a massive black hole at 30% of the speed of light,” marveled Oliver Pfuhl, a scientist at the Max Planck Institute for Extraterrestrial Physics.
In 2018, astronomers discovered several bizarre objects at the Galactic Center using 12 years of data taken from W. M. Keck Observatory on Mauna Kea, Hawaii. The objects are concealing their true identity behind an opaque screen of dust; they look like gas clouds, but behave like stars. “These compact dusty stellar objects move extremely fast and close to our Galaxy’s supermassive black hole. It is fascinating to watch them move from year to year,” said astronomer Anna Ciurlo at UCLA. “How did they get there? And what will they become? They must have an interesting story to tell.” (more…)
“The fate of black holes in a quantum theory of gravity is, in my view, the most important problem in theoretical physics,” said Jorge Pullin, the Horace Hearne professor of theoretical physics at LSU.
Astronomers studying the motions of galaxies and the character of the cosmic microwave background radiation came to realize in the last century that most of the matter in the universe was not visible. About 84 percent of the matter in the cosmos is dark matter, much of it located in halos around galaxies. It was dubbed dark matter because it does not emit light, but it is also mysterious: it is not composed of atoms or their usual constituents like electrons and protons.