The Universe Revealed by Subaru Telescope Ⅵ

Black Holes and γ-ray Bursts

Although it has been predicted that there are probably massive black holes at the hearts of many large galaxies, their existence lies hidden behind clouds of gas and dust. As a supermassive black hole (one with a mass about a million times that of our Sun) violently swallows matter from surrounding space, it radiates strong energy. However, if the heart of the galaxy is obscured by gas and dust, it is difficult to observe those energy emissions. The latest observations at the Subaru Telescope provide us with clear evidence that these black holes do exist in many brightly shining galaxies.


The Galactic Center


This image uses a false-color scheme to show data in the mid-infrared from a region that is seven light-years long and five light-years wide. The bright dot in the center of the figure is thought to be a region that is heated by the stars' interaction with the surrounding dust. The actual nucleus of the Milky Way Galaxy is the darker area just to the right of center in this image. This is the likely home of our galaxy's central black hole.

There is strong evidence that the center of our Milky Way Galaxy harbors an enormous black hole. Not even light can escape from the gravity well of a black hole, yet we are still able to learn about them by observing the energy produced when interstellar matter is heated as it falls into black holes. In addition, the gravitational influence of a black hole on the gas and stars around it tells us much about its characteristics. Due to the extraordinary amount of gas and dust that hides the center of our galaxy from us, it is impossible to use visible light as a tool for observation. In contrast, infrared wavelength especially the mid-infrared (radiation produced by the interaction of dust and nearby stars) is observable and COMICS(Cooled Mid-Infrared Camera and Spectrograph) has succeeded in precisely imaging the center of the Milky Way Galaxy.



Origin of the Mysterious γ-ray Bursts


The comparison between the optical spectrum (black lines) of supernova SN2003dh which was discovered along with the γ-ray burst (GRB030329) and the spectrum of the object known as an extreme supernova (red and green lines).

γ-ray bursts, which are among the largest and most energetic phenomena ever recorded, have been a mystery since their discovery almost 30 years ago. Over the past few years, it has become clear that a special type of supernova or hypernova may be linked to the occurrence of γ-rays. After GRB030329 was detected by the HETE-2 satellite, Subaru Telescope made repeated observations of the source by using visual spectrograph; it also took polarization data of the afterglow of the event. The Subaru Telescope has made significant contributions in the quest to confirm the relationship between supernovae and γ-ray bursts.





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