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Sagittarius A*, abbreviated as Sgr A* (/ ˈ s æ dʒ ˈ eɪ s t ɑːr / SADGE-AY-star [3]), is the supermassive black hole [4] [5] [6] at the Galactic Center of the Milky Way.Viewed from Earth, it is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, [7] visually close to the Butterfly Cluster (M6) and Lambda Scorpii.
The supermassive black hole Sagittarius A*, imaged by the Event Horizon Telescope [11] Astronomers now have evidence that there is a supermassive black hole at the center of the galaxy. [12] Sagittarius A* (abbreviated Sgr A*) is agreed to be the most plausible candidate for the location of this supermassive black hole.
One of the most studied stars is S2, a relatively bright star that also passes close by Sgr A*. As of 2020 [update] , S4714 is the current record holder of closest approach to Sagittarius A*, at about 12.6 astronomical units (1.88 × 10 9 km), almost as close as Saturn gets to the Sun, traveling at about 8% of the speed of light.
A black hole is a massive, compact astronomical object so dense that its gravity prevents prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. [2] The boundary of no escape is called the event horizon.
S2, also known as S0–2, is a star in the star cluster close to the supermassive black hole Sagittarius A* (Sgr A*), orbiting it with a period of 16.0518 years, a semi-major axis of about 970 au, and a pericenter distance of 17 light hours (18 Tm or 120 au) – an orbit with a period only about 30% longer than that of Jupiter around the Sun, but coming no closer than about four times the ...
It is also slightly eclipsed by an accretion disc around the black hole. The system usually does not produce a significant amount of x-rays, but undergoes outbursts when the x-ray luminosity increases due to accretion onto the black hole driving superluminal jets. [7] V4641 Sgr is a source of ultra-high-energy gamma rays. [8]
[1] [2] The stars δ Sgr (Kaus Media), ε Sgr (Kaus Australis), ζ Sgr (Ascella), and φ Sgr form the body of the pot; λ Sgr (Kaus Borealis) is the point of the lid; γ 2 Sgr (Alnasl) is the tip of the spout; and σ Sgr (Nunki) and τ Sgr the handle. These same stars originally formed the bow and arrow of Sagittarius. [3]
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