Astronomers have discovered a black hole with a mass about 33 times greater than that of the Sun.
It is the largest one known to be in the Milky Way aside from the supermassive black hole lurking at the centre of our galaxy.
The newly identified black hole is located about 2,000 light-years from Earth — relatively close in cosmic terms — in the constellation Aquila, and has a companion star orbiting it.
Black holes are extraordinarily dense objects with gravity so strong that not even light can escape, making it difficult to spot them.
Gaia BH3 discovered through its companion star
This black hole was identified because it caused a wobbling motion in its companion star — something observed as part of the European Space Agency's Gaia mission.
Data from the European Southern Observatory's Chile-based Very Large Telescope and other ground-based observatories were used to verify the black hole's mass.
University of Sydney professor Joss Bland-Hawthorn, who conducted dynamic modelling of the Milky Way for the research, said the discovery excited scientists "for a number of reasons".
"This particular black hole is extraordinary because it seems to have fallen into the Milky Way from outside," Professor Bland-Hawthorn told ABC News Channel.
"It was formed in a small galaxy that was in orbit around our Milky Way and that little galaxy fell in and brought this black hole with it, which makes this black hole very ancient."
"We think the black hole is at least 12 billion years [old], maybe even older, in a universe that's 14 billion years old."
The black hole, called Gaia BH3, and its companion are travelling within the galaxy in the opposite direction of how stars typically orbit in the Milky Way.
Gaia BH3 probably formed after the death of a star that was more than 40 times as massive as the Sun, the researchers said.
Professor Bland-Hawthorn said scientists believed Gaia BH3 was dormant.
"Blackholes are massive objects, so dense that not even light gets away from them," Professor Bland-Hawthorn said.
"But you do see their presence by things that spin around them, like gas or stars. So we think of a dormant black hole where there's nothing going on.
"We've got stuff spinning around it but not firing up the black hole causing this thing around it to explode.
"They're extremely hard to detect and, in fact, we detect them by the effect they have on things around them."
Gaia BH3 the largest of known stellar black holes in galaxy
Black holes that result from the collapse of a single star are called stellar black holes. Gaia BH3 is the largest-known stellar black hole, according to astronomer and study co-author Tsevi Mazeh of the Tel Aviv University in Israel.
Howver, Stellar black holes are dwarfed in size by the supermassive black holes inhabiting the centre of most galaxies. One such black hole called Sagittarius A* is located at the heart of the Milky Way. It possesses 4 million times the mass of the Sun and is located about 26,000 light-years from Earth.
Gaia BH3's progenitor star was composed almost entirely of hydrogen and helium. Stars in the early universe had such a chemical composition, known as low metallicity.
This star formed relatively early in the universe's history — perhaps 2 billion years after the big bang.
When that star exploded at the end of its life span, it blasted some material into space while the remnant violently collapsed and formed a black hole.
Scientists are not sure just how big stellar black holes can be.
Reuters/ABC
