Science. – The first stellar ‘ghost’, possibly a floating black hole

Madrid, 10 (European press)

The discovery by a team led by the University of California, Berkeley, came from observing the brightness of a farther star in which its light is distorted by an object’s strong gravitational field, hence the so-called microgravitational lensing.

The team, led by graduate student Casey Lamm and Jessica Lu, assistant professor of astronomy, estimates that the mass of the invisible compact object is between 1.6 and 4.4 times the mass of the Sun.

Since astronomers believe that the remnants of a dead star must weigh more than 2.2 solar masses to collapse into a black hole, the researchers warn that the object could be a neutron star, not a black hole. Neutron stars are also very dense and compact objects, but their gravity is balanced by the internal pressure of neutrons, which prevents further collapse into a black hole.

Whether it is a black hole or a neutron star, the object is the first dark stellar remnant, a stellar “ghost”, discovered wandering the galaxy without pairing up with another star.

“This is the first floating black hole or neutron star to be detected using a gravitational microlensing,” Lu said in a statement. “By using the finer lens, we can examine and weigh these single, compressed objects. I think we’ve opened a new window on these dark objects, which cannot be seen any other way.”

Determining how many of these compact objects inhabit the Milky Way will help astronomers understand the evolution of stars, in particular how they die, and the evolution of our galaxy, possibly revealing whether any of the invisible black holes are black holes. Cosmologists believe that large numbers were produced during the Big Bang.

The analysis by Lamm, Lu and their international team has been accepted for publication in The Astrophysical Journal Letters.

The optical data came from two studies of microlensing: the Optical Gravitational Lens Experiment (OGLE), which uses a 1.3-meter telescope in Chile operated by the University of Warsaw, and the Observational Microlensing Experiment in Astrophysics (MOA). A 1.8-meter telescope in New Zealand operated by Osaka University.