Tuorla Observatory News, 20th October 2006:

OJ continues to surprise

The binary black hole AGN, OJ287 continues to provide astronomers with surprises. Long term monitoring of OJ287's optical brightness now indicates that the system may be precessing very rapidly, setting a record for general relativistic precession of orbits.

OJ287 is thought to be a binary black hole in the centre of a distant galaxy. Both black holes are very heavy -- one equivalent to some 18 billion times the mass of the Sun, while the other weighs in at a mere 100 million times the mass of the Sun. The smaller black hole is believed to be in a quite eccentric orbit around the heavier, and prediodically passing through the regions close to the centre of the system, where gas has collected into a so-called accretion disk. The passing of the lighter black hole through this disk causes huge outbursts of energy in the system, showing up at all frequencies from radio to optical and X-ray. The outbursts are seen approximately every twelve years and occur as double peaks. OJ287 is going through such an outburst at the moment, and observatories world-wide are closely monitoring it during this particularly interesting phase.

Now an international team of astronomers led by Mauri Valtonen has analysed the "light curves" of OJ287 at Tuorla Observatory in order to determine by how much the elliptical orbit of the lighter black hole precesses with each orbit. This effect, perhaps best known for the planet Mercury, was one of the key early tests of General Relativity. Mercury's precession because of this effect is minuscule -- its orbit precessing by only 43 seconds of arc per century. Binary pulsars are much more "relativistic" systems, and orbital precession rates can amount to a few degrees per annum.

Mauri Valtonen's team has discovered the OJ287 sets a hard to beat record, precessing by a whopping 37.5 to 39.1 degrees per orbit. If confirmed, this sytsem probes general relativity under the most extreme conditions to date. Previous estimates of the precession rate came in at about 33 degrees per orbit, but the last outburst data have led to improved estimates. OJ287 is now expected to have a major outburst in September 2007, providing the means to check on the model. Currently OJ287 is not in outburst, but in an exceptionally low state, as it usually is between double outburst peaks.

The study has been published in the Astrophysical Journal (Valtonen et al, ApJ, vol 646, page 36, 2006) and in (Valtonen et al, ApJL, vol 643, page 9, 2006)

Very extensive information on OJ287 monitoring is available from Tuorla's monitoring pages.

OJ287's precessing orbits

The diagram shows the precession of the orbit of the lighter black hole around the heavier in the binary black hole AGN OJ287 for the period 1971-2010. A major outburst in the luminosity of the system at all wavelengths occurs roughly when the lighter black hole crosses through the accretion disk of very hot gas which has formed around the inner regions of the system. Larger image available here.

This page was last modified by  Chris Flynn  on  20/10/2006 03:20  astroweb@utu.fi