Astronomers discover smallest black hole lurking in Milky Way
Astronomers led by Song Wang from the Chinese Academy of Sciences, have discovered an unusual celestial phenomenon, potentially the smallest black hole ever detected. The discovery was made approximately 5,825 light-years away from Earth, where a red giant star was observed moving in a slow orbital dance with an invisible binary companion. The team named this intriguing find as G3425.
G3425's invisible companion: A potential black hole
The red giant star's invisible binary companion, part of the G3425 system, has sparked interest due to its lack of light emission. Wang's team analyzed the behavior of the red giant and determined that this unseen object has a mass approximately 3.6 times that of our Sun. This led them to conclude that it could be a black hole, specifically one small enough to fit into an unexplained void in data known as the lower mass gap.
G3425 challenges current theories of binary evolution
The discovery of G3425 has significant implications for our understanding of small black holes. "The rare discovery of G3425 provides evidence for the existence of mass-gap black holes in non-interacting binaries, which is hard to detect through X-ray emission," stated the researchers in their paper. They further noted that "the formation of its surprisingly wide circular orbit challenges current binary evolution and supernova explosion theories."
Understanding the formation and nature of black holes
Black holes are ultra-dense objects that form from the remnant cores of dead stars, after they run out of fuel and collapse under gravity. White dwarfs form from stars up to about eight times the mass of the Sun, with an upper mass limit of about 1.4 times the Sun's mass. Heavier objects become even more dense; these are neutron stars, up to around 2.3 solar masses (there can be a bit of overlap between the mass ranges).
The mystery of the 'mass gap' in black hole formation
The concept of a 'mass gap' arises from the observation that very few black hole candidates below five solar masses have been detected. This suggests either a difficulty in detecting them or an unknown factor preventing their formation. Unless they're actively growing — a process that creates X-radiation from the material swirling around the black hole under extreme gravitational influences — black holes are challenging to spot due to their non-emissive nature.
Gaia mission aids in detecting invisible celestial objects
The European Space Agency's Gaia mission is proving instrumental in detecting such invisible celestial objects. The long-term project aims to map the Milky Way in three dimensions, including tracking stars' motions and velocities. This allows astronomers to identify stars that appear to be orbiting with no visible partner, leading to discoveries like G3425. Wang's team utilized spectroscopy from the Chinese Academy of Science's Large Aperture Multi-Object Spectroscopic Telescope and Gaia data for their groundbreaking find.
