Wading through the wealth of data from ESA’s Gaia mission, scientists have uncovered a ‘sleeping...
To prepare for the release of the next Gaia catalogue, Data Release 4, scientists are checking the motions of billions of stars and carrying out complex tests to Âsee if anything is out of the ordinary.
The motions of stars can be affected by companions: light ones, like exoplanets; heavier ones, like stars; or very heavy ones, like black holes.
One such team was deeply engaged in this work, when their attention fell on an old giant star in the constellation Aquila, at a distance of 1926 light-years from Earth.
The exquisite quality of the Gaia data enabled scientists to pin down the mass of the black hole with unparalleled accuracy and provide the most direct evidence that black holes in this mass range exist.
Astronomers face the pressing question of explaining the origin of black holes as large as Gaia BH3. Our current understanding of how massive stars evolve and die does not immediately explain how these types of black holes came to be.
A clue to this puzzle may lie very close to Gaia BH3. The star orbiting Gaia BH3 at about 16 times the Sun-Earth distance is rather uncommon: an ancient giant star, that formed in the first two billion years after the Big Bang, at the time our galaxy started to assemble.
The companion star has very few elements heavier than hydrogen and helium, indicating that the massive star that became Gaia BH3 could also have been very poor in heavy elements.
These early stars might have evolved differently from the massive stars we currently see in our galaxy.
"What strikes me is that the chemical composition of the companion is similar to what we find in old metal-poor stars in the galaxy," explains Elisabetta Caffau of CNRS, Observatoire de Paris, also a member of the Gaia collaboration.
"We have been working extremely hard to improve the way we process specific datasets compared to the previous data release, so we expect to uncover many more black holes in DR4," concludes Berry Holl of the University of Geneva, in Switzerland, member of the Gaia collaboration.