“The new object, which appeared in May 2009, has left us scratching our heads — we’ve never seen anything quite like this before,” said Thomas Muxlow an astronomer with the Jodrell Bank Observatory of the University of Manchester about an unknown object detected in starburst galaxy M82.
“The object turned on very rapidly within a few days and shows no sign of decaying in brightness over the first few months of its existence,” said Muxlow. “The new young supernova explosions that we were expecting to see in M82 brighten at radio wavelengths over several weeks and then decay over several months, so that explanation seems unlikely.”
The plausibility of a supernova explanation was further undermined when very accurate positional monitoring by the UK network of radio telescopes, MERLIN, Galaxy Evolution Survey, tentatively detected a change in position for the object over the first 50 days. This was equivalent to an apparent superluminal motion of over 4 times the speed of light. Such large apparent velocities are not seen in supernova remnants and are usually only found with relativistic jets ejected from accretion disks around massive black hole systems.The nucleus of M82, like most major galaxies, is expected to contain an as yet undetected super-massive black hole.
The new detection lies at a position close to, but several arcseconds from the dynamical center of M82 — far enough away that it would seem unlikely that this object is associated with the central collapsed core of this galaxy. The new source could be the first radio detection of an extragalactic ‘micro-quasar’. Examples of such systems within the Milky Way are found as X-ray binaries with relativistic jets ejected from an accretion disk around a collapsed star fuelled with material dragged from a close binary companion.
However, this object would be brighter than any Galactic example yet detected, has lasted months longer than any known X-ray binary, and lies at a position in M82 where no variable X-ray source has been yet been detected.
If this object is an extragalactic micro-quasar, it would be the first that has been detected at radio wavelengths. The very high luminosity suggests that it is likely to be associated with a massive black hole system of some type; however this and its longevity imply that this type of object is extremely unusual and has not yet been seen within the Milky Way.
There have been several theories about the nature of this unknown object, but currently no theory entirely fits the observed data. The problem with the “micro quasar” theory is microquasars produce large quantities of X-rays, whereas no X-rays have been seen from the mystery object. The object is located at several arcseconds from the center of M82.
The Subaru image of M 82 central region above taken with infrared telescopes have found a very strong wind emanating from it — a ‘superwind’ that is composed of dusty gas and extends over many hundreds of thousands of light years (middle and bottom of image). This high-powered windstorm ejects material from the galaxy at a speed of about a half a million miles per hour, sweeping it up from the central regions and depositing it far and wide over the galaxy and beyond. The contents of this material are seeds for solar systems like our own, and perhaps for life itself. The dusty superwind glows brightly in the infrared, because billions of bright, newly-formed stars heat it up.
An exciting question that remains to be answered is whether or not M 82 hosts an actively growing supermassive black hole. Team members Mark Birkinshaw and Diana Worrall of the University of Bristol note, “Detailed analysis of the new infrared data combined with X-rays does not find any such object.” However, all large galaxies could well contain these monsters, which are known to grow and evolve in conjunction with stars. The team concludes that M 82 may be no exception, and the search for its big black hole must continue.
The Daily Galaxy, Sam Cabot via Royal Astronomical Society (RAS) and naoj.org