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Supermassive Black Hole March 3, 2010

Posted by isotopeeffect in Uncategorized.
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Not the track by Muse, but the object at the center of our galaxy, in the region known as Sgr A* (pronounced “Sagittarius A-star”).

Here it is in action:

What you see in this video clip are the trajectories of stars in the vicinity of Sgr A*, plotted from observations over a period of about 15 years. (You can see the date updating in the top left-hand corner.) This is very close to the orbital period of the star S0-2, which can be seen describing an almost complete ellipse during the period of the observations. At its closest approach, S0-2 is 17 light hours from the black hole itself, and reaches a velocity of about four percent of the speed of light. (Fast!)

Sgr A* (and therefore the galactic center) is about 25,000 light years away from us. The mass of the black hole is estimated to be about 4 million solar masses.

The observations were made by a team led by Andrea Ghez at UCLA, primarily using the Keck telescopes, situated near the summit of Mauna Kea in Hawai’i. The telescopes are not “just” telescopes, but are equipped with a suite of instruments including cameras and spectrometers sensitive to different regions of the electromagnetic spectrum. These particular measurements use NIRC, the Near InfraRed Camera, which is “so sensitive it could detect the equivalent of a single candle flame on the moon” (according to Wikipedia), using a wavelength of 2.2 μm. Specialized adaptive optics ensure that the measurements are made with the highest resolution possible (the so-called diffraction limit). The measurements are made in this spectral region rather than the visible region because visible light is strongly attenuated by interstellar dust.

If our galaxy, which is rather inactive (fortunately for us), has a black hole at its center, goes the reasoning, so do almost all galaxies. (Here’s what the Goddard Space Flight Center has to say about active galaxies.)

Links to PDF preprints of several papers are given on Prof. Ghez’s web site.



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