CFHT, Current Image of the Week


February 28th, 2000

A Black Hole at the Center of our Galaxy

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A Black Hole at the Center of our Galaxy

Credit: Image courtesy of F. Rigaut¹, R.Doyon², et al.

¹Gemini Observatory, Hawaii
²Université de Montréal, Canada

Is there a black hole or not at the center of our Galaxy? Chances are the answer is YES!

Thanks to images like this week's CFHT picture, evidence is now growing that there is indeed a massive "thing", a black hole, hiding at the center of our Milky Way. Of course, a black hole cannot be seen directly, by definition! But the object is so massive, and so small, that there are traces of its presence. For example, stars located close to the black hole have very rapid motions, they rapidly orbit a point in space where... we see nothing! It is these rapid motions that hint at the presence, and position, of a black hole at the center of our Galaxy.

This week's image shows, on the left hand side, the galactic center as it is seen by a telescope located in a good site (atop Mauna Kea for example) using normal imaging techniques. The right image shows the same field, as seen with the Canada-France-Hawaii Telescope Adaptive Optics system. The image is crisper, and a lot of details and new stars stand out. Note the diffraction rings around each star, which indicate that the ultimate resolving power of the telescope has been reached.

This image (not deconvolved) revealed the center of our galaxy with new details that allowed a team at CFHT, University of Montreal and the Dominion Astronomical Observatory (Victoria, Canada) to put new constraints on the central engine of our Galaxy. A very dense core, most probably a black hole, is believed to lie approximately at the center of this stellar field. The motion of some stars close to where the black hole is thought to be located have apparent velocities in excess of 2000 kilometers per seconds!

Technical description:

The image on the right was obtained with PUEO, the Adaptive Optics system of the Canada-France-Hawaii Telescope. A wide near-infrared filter centered at a wavelength of 2.2microns was used. This image was obtained in 1995 with MONICA, the MOntreal Near-Infrared Camera. The total field of view is only 13 X 13 arcseconds. The total integration time on this field was 15 minutes. Note the little "circle" around each star. It is called an "Airy ring" and it is a feature typical of images that are at the diffraction limit of a telescope. They indicate that the images have the best sharpness the telescope can do!

next week: The observation of a candidate for the optical counterpart of the Gamma Ray Burster GRB000301c

editors: François Ménard & Jean-Charles Cuillandre
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CFHT is funded by the Governments of Canada and France, and by the University of Hawaii.