The super massive Sagittarius A*.

What supermassive black holes really are ?

  Supermassive black holes exist at the centre of every spinning galaxy. They are very huge and continuously feed themselves off the surrounding matter. Astronomers are monitoring the colossal object called "Sagittarius A*," the supermassive black hole that exists at the centre of the Milky Way galaxy. The Sagittarius A* is a supermassive black hole at the rotational centre of the Milky Way galaxy, also known as the galactic center. The galactic centre is 26,490  100 light-years away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest. It coincides with the compact radio source Sagittarius A*. The presence of numerous stars, most notably the S2 star, has provided evidence of the presence of the Milky Way's central supermassive black hole, and has led some scientists to conclude that Sagittarius A* is beyond any reasonable doubt the site of that black hole.

So, how big our galaxy is and where the black hole is…?    

     Our galaxy, the Milky Way galaxy, is one of the galaxies in the cluster of many galaxies. It is not very huge and bright if we compare it with the largest galaxy known to us, which is IC 11O1, which has a diameter of 6 million light-years and is the single largest galaxy that has ever been found in the observable universe, as that of the Milky Way is just about 100,000 light-years. By the calculations, Sagittarius A* is situated at the centre of it, which is nearly 26000 light-years away from us, and by the calculations, it is roughly 4.1 million times more massive than the sun.

 

 How we can see the Sagittarius A* ?

  Astronomers have been unable to observe Sagittarius A* in the optical spectrum because of the effect of 25 magnitudes (i.e., one unit less brightness of an object in a defined passband) of extinction by dust and gas between the source and Earth, and also because the black hole itself cannot be seen because it acts as a one-way path even for light. But it is possible to detect radiation blazing from gas and dust just outside the "event horizon" as they are accelerated, which is about 1/10 the speed of light. The brightness of the black hole at the heart of our galaxy has increased by 75 percent—the brightest it has been since scientists first started studying it more than 20 years ago, as it is continuously feeding the matter surrounding it. It is said that more gas is falling into the black hole, and that leads to higher amounts of accretion, which leads to it being brighter. Sagittarius A* is on the verge of being imaged by the Event Horizon Telescope. When it’s accomplished, the picture of the Milky Way’s supermassive black hole, Sagittarius A*, will be the greatest success for all of us.