University of Florida

Black Holes

Black Hole Image credit: NASA
As the powerhouses behind relativistic jets and much of the high-energy photon and cosmic ray emission in the Universe, black holes and neutron stars are a fundamental influence on many astrophysical phenomena. One of the overall goals of our group is to understand the populations and evolution of X-ray binaries (XRBs), and the physical conditions/processes which lead to the formation of relativistic jets in some (possibly all!) of them. While we have studied relativistic outflows from black hole systems from stellar-mass to supermassive for several decades, the details of the mechanism which accelerates and collimates such a jet at nearly the speed of light out of the black hole potential well remains a mystery.

The scientific path we take employs multi-wavelength studies of the physics of compact objects (particularly microquasars) and the populations and origins of compact objects in our Galaxy and beyond.  With the addition of THOUSANDS of new X-ray sources recently discovered in the Galactic Center, we have the opportunity to expand our sample size of accreting compact objects in general, and black hole binaries in particular, by an order of magnitude, enabling the use of population statistics to constrain the origin and evolution of even rare classes of X-ray binary such as microquasars.

Past Highlights
  • Our early high time-resolution infrared/X-ray work on this subject (Eikenberry et al., 1998a,b) established a direct link between time-resolved activity in the inner accretion disk of a black hole system and the formation of relativistic jet outflows – a connection long suspected on theoretical grounds but never previously confirmed by direct observations. This work resulted in an AAS press conference, with coverage in the New York Times, CNN Headline News, BBC World Report, and many newspapers worldwide.  Click here for the NASA animation.  
  • In 1999, we discovered another disk/jet connection between X-ray oscillations from GRS 1915+105 and faint infrared flares (Eikenberry et al., 2000a) with different X-ray amplitudes and spectral evolution and IR light curves and X-ray/IR timing offsets than the previously observed disk/jet interactions (Eikenberry et al., 1998a,b; Mirabel et al., 1998; Fender & Pooley, 1998). This discovery and further analysis of published data led to the conclusion that GRS 1915+105 alone exhibits at least three distinct modes of jet formation and disk/jet interaction (Eikenberry, 2001) – an initially controversial conclusion which has been cemented by our continued observational work in 2002 and 2003 (Rothstein et al., 2005).
  • Our HST/NICMOS observations of an outburst of GRS 1915+105 revealed even fainter/faster IR flickering from GRS 1915+105 which is uncorrelated with any similar X-ray activity – a first even in this complexly-variable system – and which appears to arise in the very base of the jet-forming region within <2.5 AU of the central compact object (Eikenberry et al., 2008).
  • With collaborators in France, we have shown the consistency of jet-related X-ray quasi-periodic oscillations (QPO) with general relativistic effects near the black hole in GRS 1915+105 (Mikles et al., 2009).
  • In 2006, our group made the first definitive identification of an IR counterpart to one of the Galactic Center X-ray sources (Mikles et al., 2006) via spectroscopy with SpeX at IRTF. Since then, we have added even more such sources (Dewitt et al., 2010; Dewitt et al., 2013)

Current Projects
  • Galactic Center IR Survey
    Studies of populations of X-ray binaries and surveys for new systems provide a powerful complement to investigations of individual sources in understanding the origin, formation, and evolution of X-ray binaries and the physical conditions/processes which lead to the formation of relativistic jets in these galactic powerhouses. Of the ~2300 X-ray point sources discovered by Chandra in the central 40 pc of the Galaxy, ~80% of these faint, X-ray hard sources are physically located within the Nuclear Bulge of the Milky Way.  We are using near-IR imaging and spectroscopy to survey these targets, including a planned comprehensive survey with FLAMINGOS-2 to provide spectra of all ~2000 possible IR counterparts in ~10 nights of observing time on Gemini South.  With these spectroscopic observations, we ultimately expect to identify ~200-300 previously unknown X-ray binaries -- this will increase the number of X-ray sources with identified optical/IR counterparts in the GC by nearly two orders of magnitude, and will in fact increase the entire known Galactic sample of such sources by >50%.

  • Relativistic Jet Formation in Microquasars
    We hypothesize that the cycles of X-ray dips/spikes accompanied by long-wavelength flares which first brought the “Rosetta Stone” label for GRS 1915+105 are in fact a combination of continuous jet outflows terminated by magnetically-driven CME-like ejections with observable signatures of magnetic reconnection.  We are developing detailed models for this behavior, along with observational tests/implications for them. This includes high-time resolution IR photometry and polarimetry with CIRCE combined with simultanoues X-ray observations. We expect to publish some fascinating results on V404 Cyg very soon.