Peering Into The Black Hole At The Heart Of The Milky Way

Peering Into The Black Hole At The Heart Of The Milky Way.

No astronomer or satellite has been able to peer into the Milky Way’s black hole. It is just too far from Earth! Scientists, in this article, discuss and explore ways to enable them to study what is at the centre of our galaxy. The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A), is revealed in the images below. Astronomers used NASA’s Chandra X-ray Observatory to take a major step in understanding why material around Sgr A is extraordinarily faint in X-rays. The large image contains X-rays from Chandra in blue and infrared emission, and from the Hubble Space Telescope in red and yellow. The inset shows a close-up view of Sgr A* in X-rays only, covering a region half a light year wide. The diffuse X-ray emission is from hot gas captured by the black hole and being pulled inwards. This hot gas originates from winds produced by a disk-shaped distribution of young massive stars observed in infrared observations.

If we return to radio observations of Sgr A, the image is from the Very Large Array, and it shows that in the central few parsecs there is a spiral structure made up of gas that is surrounding the central point source (Sgr A*). The gas appears to be rotating around Sgr A*, which is a clue about the nature of this object.

These new findings are the result of one of the biggest observing campaigns ever performed by Chandra. During 2012, Chandra collected about five weeks worth of observations to capture unprecedented X-ray images and energy signatures of multi-million degree gas swirling around Sgr A*, a black hole with about 4 million times the mass of the Sun. At just 26,000 light years from Earth, Sgr A* is one of very few black holes in the universe where we can actually witness the flow of matter nearby. The researchers infer that less than 1% of the material initially within the black hole’s gravitational influence reaches the event horizon, or point of no return, because much of it is ejected. Consequently, the X-ray emission from material near Sgr A* is remarkably faint, like that of most of the giant black holes in galaxies in the nearby Universe. Credit: NASA.

Now let us consider the nature of Sgr A* in particular. This object emits a large amount of radiation in IR, X-rays, and gamma-rays. It appears to be motionless, but we see gas apparently orbiting the source. Recently, observations of stars also found to be orbiting Sgr A* have given us significant new insight into the nature of this object. Using the highest resolution IR cameras available, astronomers have repeatedly observed the stars orbiting around Sgr A*. They have measured the orbit of a star that comes within 17 light-hours of the object in the core of our Galaxy, which is a distance that is only a few times larger than the orbit of Pluto around the Sun. Using Kepler’s laws, if we measure the period and semi-major axis of this star’s orbit around Sgr A*, we can calculate the mass of this object. The mass that results from the study of this star and other nearby stars is 4 million solar masses! The only type of object that astronomers believe can have a mass of approximately 4 million stars, but a radius of about 100 AU, is a black hole. Clearly the supernova explosion of one star could never produce a single black hole with a mass so large, so this object must have formed in a different manner. Sgr A* is one example of a class of objects called Super-Massive Black Holes.

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