By Ron Cowen
HEIDELBERG, Germany — If it’s not as dead as a doornail, the gravitational monster at the Milky Way’s center is clearly lethargic. The galaxy’s supermassive black hole barely radiates, and certainly doesn’t hurl jets of material into space — signs that it has been on a starvation diet.
And a new study suggests that the central black hole barely spins, either.
Black hole spin doctors Avery Broderick of the Canadian Institute for Theoretical Astrophysics in Toronto and his colleagues, including Avi Loeb of Harvard University’s Institute for Theory and Computation, base their tentative findings on millimeter-wave radio emissions from the galactic center recorded by a trio of radio telescopes. Collectively, the electronically linked radio dishes act as a single giant dish, or interferometer, enabling astronomers to start homing in on the black hole’s millimeter-wave emissions. That radiation penetrates the dust and gas that concentrate in the crowded central region of the galaxy.
The emissions are believed to be generated by the material at the inner edge of the accretion disk, the whirlpool of matter that spirals into and fuels the black hole. Combing the millimeter-wave data — which is still relatively sparse — with extensive modeling of the expected emissions suggests that the supermassive black hole spins slowly or not at all, Loeb reported December 6 at the biannual Texas Symposium on Relativistic Astrophysics. The researchers also describe their study in an article posted at arXiv.org on November 15 (http://arxiv.org/abs/1011.2770).