Astronomers detect the Milky Way’s second largest known black hole

Astronomers detect the Milky Way’s second largest known black hole

Astronomers have discovered a black hole with a mass about 33 times that of our sun, the largest known in the Milky Way other than the supermassive black hole lurking at the center of our galaxy.

The newly identified black hole lies about 2,000 light-years from Earth – relatively close in cosmic terms – in the constellation Aquila, and has a companion star orbiting it, researchers said on Tuesday. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

Black holes are incredibly dense objects with such strong gravity that light cannot escape, making them difficult to detect. This one was identified through observations made in the European Space Agency’s Gaia mission, which created a large stellar census, as it caused a wobbly motion in its companion star. Data from the Chile-based Very Large Telescope at the European Southern Observatory and other ground-based observatories were used to confirm the mass of the black hole.

“This black hole is not only very large, it is also very strange in many respects. It is really something we never expected to see,” said Pasquale Panuzzo, a research engineer at the French research agency CNRS who works at the Observatoire de Paris and lead author of the study published in the journal Astronomy & Astrophysics.

For example, the black hole, called Gaia BH3, and its companion move in the galaxy in the opposite direction to the way stars normally orbit in the Milky Way.

Gaia BH3 may have formed after the death of stars larger than 40 solar masses, the researchers said.

A black hole that results from the collapse of a single star is called a stellar black hole. Gaia BH3 is the largest known stellar black hole, according to astronomer and study co-author Tsevi Mazeh of Tel Aviv University in Israel.

Stellar black holes are dwarfed in size by the supermassive black holes that inhabit the centers of most galaxies. A black hole called Sagittarius A*, or Sgr A*, lies at the center of the Milky Way. It has 4 million times the mass of our sun and lies about 26,000 light years from Earth.

Gaia’s progenitor star BH3 is composed almost entirely of hydrogen and helium. The stars in the early universe had such a chemical composition, known as low metallicity. This star was formed relatively early in the history of the universe – perhaps 2 billion years after the Big Bang event.

When the star explodes at the end of its lifespan – called a supernova – it blasts some material into space while the rest violently collapses to form a black hole.

The artist’s impression compares three neighboring stellar black holes in our galaxy: Gaia BH1, Cygnus X-1 and Gaia BH3, which are 10, 21 and 33 times the mass of the Sun, respectively. PHOTO: REUTERS

The discovery of Gaia BH3, according to Panuzzo, supports a model of stellar evolution that suggests that massive stellar black holes can be produced only by low-metallicity stars like this progenitor star.

Gaia’s companion star BH3, as old as the other, is about 76% the mass of the sun and slightly cooler, but about 10 times more luminous. It orbits the black hole on an elliptical path at distances that vary between about 4.5 times the distance between Earth and the sun – a measure called an astronomical unit (AU) – and 29 AU. By comparison, Jupiter orbits about five AU from the sun and Neptune about 30 AU.

“The surprising result for me is the fact that the chemical composition of this companion star does not show anything special, so it is not affected by the black hole supernova explosion,” said astronomer and study co-author of the Observatoire de Paris Elisabetta Caffau. .

Scientists aren’t sure how big the star’s black hole is.

“The maximum mass for a stellar black hole is a matter of active scientific debate,” Panuzzo said.