BLACK HOLE

A black hole is a region of spacetime where gravity is so strong that nothing, not even light and other electromagnetic waves,is capable of possessing enough energy to escape it. Einstein's theory of general relativity predicts that is capable of possessing enough energy to escape it. Einstein's theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. A black hole has a great effect on the fate and circumstances of an object crossing it, but it has no locally detectable features according to general relativity.In many ways, a black hole acts like an ideal black body, as it reflects no light.

Sagittarius A* Black hole

This supermassive black hole is located at the center of our Milky Way galaxy. It's about 4.3 million times the mass of the Sun.

Sagittarius A* (pronounced "A-star") is a supermassive black hole located at the center of the Milky Way galaxy. It is situated about 26,000 light-years from Earth in the constellation Sagittarius. This black hole has an estimated mass of about 4.3 million times that of the Sun, making it one of the most massive objects in our galaxy.

Sagittarius A* was discovered through observations of its gravitational effects on nearby stars and gas clouds, which orbit the black hole at incredibly high speeds. These observations were crucial in providing evidence for the existence of black holes. The region around Sagittarius A* is characterized by intense radio, infrared, X-ray, and gamma-ray emissions, which arise from the accretion of matter onto the black hole.

In 2022, the Event Horizon Telescope (EHT) collaboration released the first image of Sagittarius A*'s event horizon, providing a groundbreaking view of this enigmatic object. The image confirmed theoretical predictions about the appearance of black holes and further solidified our understanding of these cosmic phenomena.

V404 Cygni Black hole

One of the first black hole candidates discovered, Cygnus X-1 is a stellar-mass black hole in the Cygnus constellation, and it is part of a binary system with a massive star.

V404 Cygni is a microquasar and a binary system in the constellation of Cygnus. It contains a black hole with a mass of about 9 M☉ and an early K giant star companion with a mass slightly smaller than the Sun. The star and the black hole orbit each other every 6.47129 days at fairly close range. Due to their proximity and the intense gravity of the black hole, the companion star loses mass to an accretion disk around the black hole and ultimately to the black hole itself.

The "V" in the name indicates that it is a variable star, which repeatedly gets brighter and fainter over time. It is also considered a nova, because at least three times in the 20th century it produced a bright outburst of energy. Finally, it is a soft X-ray transient because it periodically emits short bursts of X-rays.

The system was first noted as Nova Cygni 1938 and given the variable star designation V404 Cygni. It was considered to be an ordinary "moderately fast" nova although large fluctuations were noted during the decline. It was discovered after maximum light, and the photographic magnitude range was measured at 12.5–20.5.

GRO J1655-40 Black hole

A well-studied microquasar in a binary system with a normal star, known for its relativistic jets and X-ray emissions.

GRO J1655 40 is a binary star consisting of an evolved F-type primary star and a massive, unseen companion, which orbit each other once every 2.6 days in the constellation of Scorpius. Gas from the surface of the visible star is accreted onto the dark companion, which appears to be a stellar black hole with several times the mass of the Sun. The optical companion of this low-mass X-ray binary is a subgiant F star.

Along with GRS 1915+105, GRO J1655 40 is one of at least two galactic "microquasars" that may provide a link between the supermassive black holes generally believed to power extragalactic quasars and more local accreting black hole systems. In particular, both display the radio jets characteristic of many active galactic nuclei.

For comparison, the Sun and other nearby stars have typical speeds on the order of 20 km/s relative to the average velocity of stars moving with the galactic disk's rotation in the solar neighborhood, which supports the idea that the black hole formed from the collapse of the core of a massive star. As the core collapsed, its outer layers exploded as a supernova. Such explosions often seem to leave the remnant system moving through the galaxy with unusually high speed.

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