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Astronomers have detected the largest stellar black hole in the Milky Way galaxy, with a mass 33 times that of the Sun. It is also the second closest black hole to Earth, sitting just 2,000 light years away from the planet.

About the newly discovered stellar black hole “Gaia BH3”:

• “Gaia BH3” stellar black hole has dethroned Cygnus X-1, which is 21 times as massive as the Sun, to become the most massive black hole of stellar origin in the Milky Way.
• It sits in the Aquila constellation. Gaia is a Latin word that means “the eagle”.
• Nearly all stellar black holes were found because they exist in binaries or pair up with a companion star.
• The more massive of the two likely evolves into a black hole, with its companion orbiting it.
• Gaia BH3 was observed, causing an odd ‘wobbling’ motion on the companion star orbiting it.
• Researchers used data from ground-based observatories, including from the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on ESO’s VLT located in Chile’s Atacama Desert.
• These observatories studied key properties of the companion star, which allowed astronomers to measure the mass of BH3 precisely.

How are black holes formed?

• Black holes are formed when stars reach the end of their lives. 
• Most of these stars inflate, lose mass, and cool down to become “white dwarfs,” but others lose less mass and don’t contain heavy elements. 
• These stars are called ‘metal-poor stars’, and instead of becoming white dwarfs, they collapse in on themselves and form a black hole.
• It indicates that the star that collapsed to form a Gaia BH3 black hole must have been a metal-poor star.
• The "wobbly" star orbiting it can provide more clues, as stars in pairs tend to be similar.
• Interestingly, the wobbly star is also a metal-poor star.

About Gaia mission:

• Gaia was launched in 2013 from the European Spaceport in Kourou, French Guiana, on a Soyuz-STB/Fregat-MT launch vehicle.
• Its goal was to build our galaxy's largest, most precise three-dimensional map by surveying nearly two billion objects.
  • The mission also involves studying more than one million distant quasars and providing stringent new tests of Albert Einstein’s General Theory of Relativity.
• Gaia monitors each of its target stars about 14 times per year.
  • It is precisely charting their positions, distances, movements, and changes in brightness.
• Gaia is creating an extraordinarily precise three-dimensional map of nearly two billion objects throughout our Galaxy and beyond, mapping their motions, luminosity, temperature and composition.
  • This huge stellar census is providing the data needed to tackle an enormous range of important open questions relating to the origin, structure and evolutionary history of our Galaxy.
  • For example, Gaia is identifying which stars are relics from smaller galaxies long ago ‘swallowed’ by the Milky Way.
  • By watching for the large-scale motion of stars in our Galaxy, it is also probing the distribution of dark matter, the invisible substance thought to hold our Galaxy together.
• Gaia is achieving its goals by repeatedly measuring the positions of all objects down to magnitude 20 (about 400,000 times fainter than can be seen with the naked eye).
• For all objects brighter than magnitude 15 (4000 times fainter than the naked eye limit), Gaia is measuring their positions to an accuracy of 24 microarcseconds.
  • This is comparable to measuring the diameter of a human hair at a distance of 1000 km.
• At its heart, Gaia contains two optical telescopes that work with three science instruments to determine the location of stars and their velocities precisely and to split their light into a spectrum for analysis.