Ultra low-mass black hole uncovered
1 Nov 2019
Astrophysicists say they have discovered evidence of the smallest black hole ever detected – just 3.3 times the mass of our sun.
Ohio State University researchers believe the ultra low mass black hole – which is in a binary system about 10,000 light years away in the Auriga constellation – may fit into a completely new class of black holes.
Professor Todd Thompson at the Ohio State University, said: "We're showing this hint that there is another population out there that we have yet to really probe in the search for black holes.
“If we could reveal a new population of black holes, it would tell us more about which stars explode, which don't, which form black holes, which form neutron stars. It opens up a new area of study."
Professor Thompson’s team studied data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), which collected light from around 100,000 stars in the Milky Way.
The APOGEE project collected light spectra using high-resolution, high signal-to-noise infrared spectroscopy. Changes in light spectra detected from a star – a shift toward bluer wavelengths, for example, followed by a shift to redder wavelengths – can indicate that it is orbiting an unseen companion, such as a black hole.
They found a giant star that they believe is in orbit around a binary companion – one likely much smaller than the known black holes in the Milky Way, but bigger than most known neutron stars.
Neutron stars are generally no bigger than about 2.1 times the mass of the sun – if they were above 2.5 times the sun's mass, they would collapse to a black hole.
The team said that if their new discovery is not a non-interacting low-mass black hole, it is an unexpectedly massive neutron star.
The discovery redefines the quest to build a census of all the black holes in the Milky Way galaxy.
“There may be a population of similarly hidden black holes that have been missed by x-ray observations,” says the team’s paper, which was published in Science.
