The formation  of relativistic jets by an accreting compact object is one of the  fundamental mysteries of astrophysics. Although the theory is poorly  understood, observations of relativistic jets from systems known as  microquasars have led to a well established phenomenology. Relativistic  jets are not expected to be produced by sources with soft or supersoft  X-ray spectra, although two such systems are known to produce relatively  low-velocity bipolar outflows.  

  We report the  optical spectra of an ultraluminous supersoft X-ray source (ULS) in the  nearby galaxy M81 (M81 ULS-1). Unexpectedly, the spectra show  blueshifted, broad Hα emission lines, characteristic of baryonic jets  with relativistic speeds. These time-variable emission lines have  projected velocities of about 0.17 c, and seem to be similar to those  from the prototype microquasar SS 433. Such relativistic jets are not  expected to be launched from white dwarfs, and an origin from a black  hole or a neutron star is hard to reconcile with the persistence of M81  ULS-1’s soft X-rays. Thus the unexpected presence of relativistic jets  in a ULS challenges canonical theories of jet formation, but might be  explained by a long-speculated, supercritically accreting black hole  with optically thick outflows. 

 By with LIU Qingzhong 

Figure 1. Keck and GTC  spectra for the optical counterpart of M81 ULS-1. (a) The Keck/LRIS  spectrum taken on 2010/04/13 (black) and the GTC/OSIRIS spectrum taken  on 2015/04/08 (blue) for M81 ULS-1. Labeled over the lines are the broad  Balmer lines (Ha and Hb), the very broad blue-shifted Ha? at 5530°A and  5648A° . 

  The work by Liu,  Ji-Feng; Bai, Yu; Wang, Song; Justham, Stephen; Lu, You-Jun; Gu,  Wei-Min; Liu, Qing-Zhong; di Stefano, Rosanne; Guo, Jin-Cheng;  Cabrera-Lavers, Antonio; álvarez, Pedro; Cao, Yi; Kulkarni, Shri has  been published in Nature. Please see Nature, Volume 528, Issue 7580, pp.  108-110 (2015) for more details.http://www.nature.com/nature/journal/v528/n7580/pdf/nature15751.pdf