Black Hole lies in a visible star system

[ilan]

New closest-known black hole lies in a visible star system
EarthSky Voices in SPACE | May 6, 2020

Only 1,000 light-years away, the star system can be seen with the unaided eye.​

Artist’s concept of a black hole via ESO.​

A team of astronomers from the European Southern Observatory (ESO) and other institutes has discovered a black hole lying just 1,000 light-years from Earth. The black hole is closer to our solar system than any other found to date and forms part of a triple system that can be seen with the unaided eye. The team found evidence for the invisible object by tracking its two companion stars using the 2.2-meter telescope at ESO’s La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future.

Prior to this discovery, the closest-known black hole was A0620-00 in the constellation of Monoceros at a distance of 3,000 light years.

Petr Hadrava of the Academy of Sciences of the Czech Republic in Prague, a co-author of the research, said:

We were totally surprised when we realized that this is the first stellar system with a black hole that can be seen with the unaided eye.​

Located in the constellation of Telescopium, the system is so close to us that its stars can be viewed from the Southern Hemisphere on a dark, clear night without binoculars or a telescope.

ESO scientist Thomas Rivinius, who led the study published May 6, 2020, in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202038020), said:

This system contains the nearest black hole to Earth that we know of.​

The team originally observed the system, called HR 6819, as part of a study of double-star systems. However, as they analyzed their observations, they were stunned when they revealed a third, previously undiscovered body in HR 6819: a black hole. The observations with the FEROS spectrograph on the 2.2-meter telescope at La Silla showed that one of the two visible stars orbits an unseen object every 40 days, while the second star is at a large distance from this inner pair.

Dietrich Baade of ESO in Garching and co-author of the study, said:

The observations needed to determine the period of 40 days had to be spread over several months …​

The hidden black hole in HR 6819 is one of the very first stellar-mass black holes found that do not interact violently with their environment and, therefore, appear truly black. But the team could spot its presence and calculate its mass by studying the orbit of the star in the inner pair. Rivinius, who is based in Chile, commented:

An invisible object with a mass at least 4 times that of the sun can only be a black hole.​

Astronomers have spotted only a couple of dozen black holes in our galaxy to date, nearly all of which strongly interact with their environment and make their presence known by releasing powerful X-rays in this interaction. But scientists estimate that, over the Milky Way’s lifetime, many more stars collapsed into black holes as they ended their lives. The discovery of a silent, invisible black hole in HR 6819 provides clues about where the many hidden black holes in the Milky Way might be