Supermassive black holes with a mass of millions or even billions of suns are presumed to exist at the centre of almost every galaxy. How they came into existence and how their emerging influenced the development of the galaxies to which they belong, is currently the subject of research.
For example, ESO and MPI had confirmed that the strong radio source Sgr A* (pronounced Sagittarius A star) at the centre of the Milky Way is a super massive black hole.
Since 1992, its environment has been observed and monitored. This was done by a team focusing on the infrared wavelength. Since the advent of CCD cameras (replacing chemical film based on celluloid) the sensitivity of detectors has been extended into the red portion. By so doing, the orbits and the velocities of 28 stars have been measured.
Infrared cameras with the adaptive optics of the ESO in Chile were in use, also a spectrograph called Sinfoni, the Speckle-camera SHARP I and more instruments of the European Southern Observatory. Moreover, instruments of the Keck-Telescope in Hawaii, the New Technology Telescope and pictures taken by the Hubble-Telescope had been analysed. The result was that the massive matter at the centre of The Milky Way could only be explained by the existence of a rotating black hole. Almost 95% of the matter in that inner area of the Milky Way must have been aggregated there.
Further investigations, with the help of the "Very Large Telescope" (VLT) of the ESO, carried out by astronomers of the "Max-Planck-Institute for Extraterrestrial Physics" (MPE) in Garching near Munich, Germany, showed the ripping apart of a gas cloud. In 2013, it was the first time in history that this had seen. This cloud is now making its closest approach and new VLT observations show that it is being grossly stretched by the extreme gravitational field of the black hole (see also the cover of this book).
Stefan Gillessen, leader of the observation team said: "The gas at the head of the cloud is now stretched over more than 160 billion kilometres around the closest point of orbit to the black hole, and the closest approach is only slightly more than 25 billion kilometres from the back hole itself — barely escaping falling right in. The cloud is so stretched that the close approach is not a single event but rather a process that extends over a period of at least one year."
These photos are proof that black holes really do exist. They are also an explanation of the existence of a massive black hole at the centre in our galaxy containing approx. 4 million times the mass of The Sun. It is the closest known super massive black hole by far, hence it’s the best place to study black holes in detail.
"The most exciting thing we now see in the new observations, is the head of the cloud coming back towards us at more than 10 million km/h along the orbit about 1% of the speed of light," adds Reinhard Genzel, leader of the research group which has studied this region for nearly twenty years
The European South Observatory is employing the flag ship of its telescope fleet, to watch the black hole at the centre of our Milky Way. This is a telescope, in the Atacama desert, Chile, situated at the top of Mount Cerro
Paranal. It is the previously mentioned, the so called "Very Large Telescope", consisting of four identical telescopes having mirrors, each of which is 8 metres in diameter. The atmosphere on this mountain at a height of 2600 metres and is extremely clear and dry, making this an ideal place for an astronomer‘s observation point.
The four telescopes can be combined as one large one, allowing astronomers to achieve detail up to 25 times finer than with an individual telescope. This technique is called VLTI. The I stands for "Interferometer" and means that the light beams of the 4 huge telescopes are combined with a complex system of mirrors in underground tunnels. Here, the light paths must be maintained to within less than 1/1000 mm accuracy, over a hundred metres. With this kind of precision the VLTI can outperform the famous Hubble Space Telescope.
The Very Large Telescope VLT of ESA in Chile, consisting of
four telescopes, each eight metres in diameter (By courtesy of ESA)
Supermassive Black Holes in other galaxies:
A top candidate for supermassive black holes was found at the centre of the galaxy M87, possessing mass equivalent to about 6.6 billions times that of The Sun. Record holder is a black hole containing approx. 21 billion times the mass of our Sun, located at the centre of the galaxy NGC 4889. This was detected in 2011. Also, a huge supermassive black hole of about 20 billion times that of The Sun, is the Quasar APM 08279+5255, discovered in 2011. In contrast, the black hole within the Milky Way is relatively small at a mass equivalence of 4 millions Suns.
Because of the impossibility of optical observation of black holes, the use of Radio Telescopes for collecting the radio waves transmitted from the event horizon of black holes, is essential. Radio waves pass readily through dark clouds of hydrogen in space, allowing access to areas in the sky unavailable to traditional/classical telescopes. Moreover, radio telescopes can work together and be combined as one great "super" telescope to reveal the secrets of the sky. Better still, by way of a bonus, they are able to work during day-light.
Gerhard Börner, Physicist at the MPI of Astrophysics in Garching, Munich said that the focus on black holes meanwhile has shifted. It is now set differently.
Important questions will have to be answered in the future:
-What are the fundamental characteristics of black holes?
-Will it ever be possible to make measurements close to or even beyond the event horizon?
-How will galaxies be influenced by the existence of supermassive black holes at their centre?
In his opinion, the observations with help of X-Rays and Gamma-rays will be most suitable to answer those questions.
That kind of electromagnetic radiation is to found in the jets at the poles of black holes and around the event horizon and very importantly, easy to detect owing to the high energy level which is emitted. He thinks such observations will be the key to understanding the interior of black holes
Another X-ray satellite called NuSTAR, built by the American space agency NASA, was placed in orbit in June 2012. The satellite is designed to seek highenergetic electromagnetic waves and, when found, carry out further measurements. Because such radiation is anticipated to be emitted from black holes, this satellite will help to assess their energy levels and positions, helping to reveal further secrets. In 2015, a further satellite eROSITA will follow.
A X-ray satellite in a futuristic design: "Nuclear
Spectroscopic Telescope Array", NuSTAR, in orbit since 2012 (By courtesy of NASA)