They discover the first “invisible” black hole outside the Milky Way

Recreación artística de VFTS 243 en la Nebulosa Tarántula.

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A small, silent black hole has been discovered outside the Milky Way: According to the researchers, this is the first time that a dormant, “invisible” black hole that is not within the confines of our own galaxy has been positively identified. It is located about 158,200 light-years from Earth in the Large Magellanic Cloud.

An international team of scientists has discovered one resting black hole with stellar mass in a galaxy neighboring the Milky Way. It is the first black hole of this type to be observed outside of our galaxy. Six years of observations with the Very Large Telescope (VLT) of the European Southern Observatory (ESO) made it possible to locate it.

According to a press release, the black hole is located approximately 158,200 light years from Earth, has at least nine times the mass of our Sun and orbits a hot blue star with 25 solar masses. The new study summarizing the discovery was recently published in the journal Nature Astronomy.

A needle in a haystack

According to research group leader Tomer Shenar, the discovery is like finding a “needle in a haystack.” Dormant black holes are particularly difficult to spot because they don’t interact much with their surroundings. Although other “candidates” had previously been identified, the newly discovered black hole integrating a binary system was named VFTS 243would be the most convincing example so far.

As if that wasn’t enough, the researchers were able to determine that the star that gave birth to the black hole disappeared with no sign of a large explosion, as is usual in most cases. The structure is in Large Magellanic Cloud, a satellite galaxy of the Milky Way and a member of the so-called Local Group. It is one of the closest galaxies to the Milky Way, surpassed only by the Canis Major Dwarf Galaxy and the Sagittarius Elliptical Dwarf Galaxy in close proximity.

It is known that Stellar mass black holes They form when massive stars reach the end of their lives and collapse under their own gravity. In binary star systems, i.e. when there are two stars orbiting each other, the black hole is accompanied by a star that emits light.

a new stranger

However, many times the black hole remains “sleeping” by not producing high levels of X-rays, as black holes are currently recognized in most cases. Because of this condition, these black holes are considered “invisible”: in this case, the absence of radiation due to their inactivity is added to the difficulty of identifying any of these structures.

Sometimes the orbit of the star The companion appears to display spins around empty space, indicating the possible presence of one of these dormant black holes. But this way of recognizing them can be misleading and has led to numerous errors in the past, since it is actually very difficult to verify that the structure occupying the void orbited by the star is really a black hole and not another object is.

additionally binary system VFTS 243 could contain important clues about how black holes are formed and about the origin of black hole mergers in the cosmos, especially since the star that formed the “invisible” black hole left no trace of an explosion. One of the traditional scenarios for the formation of this type of cosmic structure is a large starburst, so this example opens up a great unknown as to the conditions of its appearance.

Relation

A X-ray quiet black hole born with a negligible kick in a massive binary system in the Large Magellanic Cloud. Shenar T, Sana H, Mahy L et al. Natural Astronomy (2022). DOI: https://doi.org/10.1038/s41550-022-01730-y

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