Galaxies merged supermassive black holes

Experts have obtained with the Subaru telescope, high-resolution images that allow us to study the emission originating from supermassive black holes ( SMBH ) in the central regions of gas-rich and bright galaxies.

K-band images

Examples of K-band images of bright and gas-rich galaxies colliding. The image size is 10 arc seconds. The individual shots clearly show the aspects of the merger process, such as the interaction of the two nuclei of galaxies.


By using the Subaru telescope (one of the telescopes of the Observatory on Mauna Kea, Hawaii), a group of astronomers led by Masatoshi Imanishi has observed the process of collision of 29 bright and gas-rich galaxies by studying in detail some supermassive black holes (supermassive black holes – SMBHs). This type is the largest among the black holes and it is believed that almost all large galaxies like our Milky Way contain at least one. Scientists have noticed that almost always at least one of the supermassive black holes present in every system examined is activated and increases in its brightness. Among the colliding galaxies analyzed, however, only some have more active SMBH at the same time. The results of the study of Japanese researchers, published in The Astrophysical Journal, show that local conditions in the vicinity of the black holes affect their activation (the amount of matter, dust, gases present) and not only the general characteristics of the galaxies at the center of which they are located.

And well-known by now that the supermassive black holes with a mass of between 1 million and 10 billion times that of the Sun are at the center of massive galaxies, which often result precisely of the collision and merger of smaller galaxies interacting (i.e. to say two or more galaxies that attract because influenced by the mutual force of gravity). This procedure facilitates the process of star formation but also the activation of supermassive black holes because they can raise a lot more matter. When the galactic material (circumstellar dust and gas) is absorbed by a supermassive black hole, the mass disk surrounding it becomes very hot because it releases gravitational energy, and therefore, it becomes very bright. And this is the process that represents the basis of active galactic nuclei: the energy that powers them is generated by matter falling into a supermassive black hole. This phenomenon is different from the nuclear reactions in the stars, but to understand and study the differences of these phenomena is not always easy because both dust and gas surround the stars in the making that the active galactic nuclei in galaxies in collision.


Herbig-Haro 30 is the prototype of a gas-rich “young stellar object” disk around a star. The dark disk spans 40 billion miles (64 billion kilometers) in this image from NASA’s Hubble Space Telescope, cutting the bright nebula in two and blocking the central star from direct view.

Source: NASA/Hubble/STScI

For this type of research, infrared observations are needed to be taken. The team of researchers used the Infrared Camera and Spectrograph (IRCS) mounted on the Subaru telescope and its adaptive optics to observe the phenomenon in K-band, an acronym that refers to the wavelength of the radiation of 2.2 micrometers, and in L-band (at a wavelength of 3.8 micrometers). These wavelengths were chosen to differentiate the activity of the supermassive black holes from that of star formation. The energy generated by the black holes income is far higher than those generated by the nuclear fusion of stars. A supermassive black hole generates a large amount of dust at high temperatures (several hundred kelvin degrees) which produces a strong, visible radiation in the L band infra.

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