In general relativity, it is predicted that there is a frame-dragging effect near a large rotating mass, such as our earth and sun. This effect was named as Lense-Thirring effect after Josef Lense and Hans Thirring. Some successful experiments have been done in our solar system to detect very weak general relativity (GR) effects, such as Lense-Thirring effect. Actually, there is a better laboratory for the test of GR, which is the nearest supermassive black hole with a mass of 4 million solar masses in our Galaxy. Recently, Han Wenbiao, an associate researcher in Shanghai Astronomical Observatory studied the effect of such spin precession on the orbital precessions of orbiting stars. His results shows that the spin precession can produce a periodic oscillation in the precession of the star's orbital plane, but has no obvious effect on the periapse shift. And in principle, the precession of this oscillating orbital plane can be observed and then the spin and spin precession of the nearest SMBH can be determined. This work has been published in “Research in Astronomy and Astrophysics” (RAA, 2014, 14, 1415).

      The star source 2 (S2), one of a group of stars labeled by S at distances from 0.001 – 0.1 milliparsec (1 parsec = 3.26 light year, 1 light year = 9460 billion km) from the Glactic center has an orbital period of about 15 years, an advance of periapse of about 0.2 degree per year based on GR and an even smaller Lense-Thirring effect. This Lense-Thirring effect on S2 is too small to detect with current technology. Once S stars with a shorter period are observed, relativistic precessions especially the Lensing-Thirring effect can be measured by astronomical observations at the 0.000001 arcsecond level in the future. An interesting but so far unaddressed problem is that the SMBH not only has spin but also spin precession.

      Recently, Han Wenbiao, an associate researcher in Shanghai Astronomical Observatory, studied the effect of such spin precession on the orbital precessions of orbiting stars. His calculations show that the spin precession can produce a periodic oscillation in the precession of the star's orbital plane, but has no obvious effect on the periapse shift. For stars with an orbital period of O(0.1) yr or less, such visible oscillations occur when the SMBH's spin-precession period ranges from about a few tens of years to hundreds of years. The period of oscillation is the same as the one of the spin precession. In principle, the precession of this oscillating orbital plane can be observed and then the spin and spin precession of the nearest SMBH can be determined.

Science Contact: Han Wenbiao, wbhan@shao.ac.cn, 34775264

News Contact: Zuo Wenwen, wenwenzuo@shao.ac.cn, 34775125