Magnetic reconnection is a process by which oppositely directed magnetic field lines passing through a plasma undergo dramatic rearrangement, converting magnetic potential into kinetic energy and heat 1,2. It is believed to play an important role in many plasma phenomena including solar flares 3,4 , star formation 5 and other astrophysical events 6 , laser-driven plasma jets 7-9 , and fusion plasma instabilities 10. Because of the large differences of scale between laboratory and astrophysical plasmas, it is often difficult to extrapolate the reconnection phenomena studied in one environment to those observed in the other. In some cases, however, scaling laws 11 do permit reliable connections to made, such as the experimental simulation of interactions between the solar wind and the Earth's magnetosphere 12. Here we report well-scaled laboratory experiments that reproduce loop-top-like X-ray source emission by reconnection outflows interacting with a solid target. Our experiments exploit the mega-gauss-scale magnetic field generated by interaction of a high-intensity laser with a plasma to reconstruct a magnetic reconnection topology similar to that which occurs in solar flares. We also identify the separatrix and diffusion regions associated with reconnection in which ions become decoupled from electrons on a scale of the ion inertial length. A major objective of laboratory astrophysics is to simulate the fundamental nature of astrophysical plasma physics processes in a laboratory environment so that certain astrophysical phenomenon can be studied in a controlled manner 13. High energy density facilities, such as high-powered lasers and Z-pinches, can provide such opportunities 14 , for example, direct measurements of opacity 15 , equations of state 16 , and photoionized plasmas 17,18 , as well as the similarity of physics, such as certain hydrodynamic phenomena of jets 19 and shocks 20 where a scaling law between astrophysical and laboratory plasma systems can be applied. As a fundamental cause of many plasma energy conversion processes, magnetic reconnection (MR) is certainly a high priority of such studies. Masuda et al. 21 observed the loop-top X-ray source in solar flares using the YOHKOH satellite and proposed that two antiparallel magnetic fields were merged above an arcade of closed loops as outflow jets from the reconnection point collided with high-density plasmas on the loop to produce a hot X-ray region. Ultraviolet 22 and X-ray 23,24 observations of plasma

X-ray spectroscopy is an important tool for understanding the extreme photoionization processes that drive the behaviour of non-thermal equilibrium plasmas in compact astrophysical objects such as black holes 1-4. Even so, the distance of these objects from the Earth and the inability to control or accurately ascertain the conditions that govern their behaviour makes it difficult to interpret the origin of the features in astronomical X-ray measurements. Here, we describe an experiment that uses the implosion 5 driven by a 3 TW, 4 kJ laser system 6 to produce a 0.5 keV blackbody radiator that mimics the conditions that exist in the neighbourhood of a black hole. The X-ray spectra emitted from photoionized silicon plasmas resemble those observed from the binary stars Cygnus X-3 (refs 7, 8) and Vela X-1 (refs 9-11) with the Chandra X-ray satellite. As well as demonstrating the ability to create extreme radiation fields in a laboratory plasma, our theoretical interpretation of these laboratory spectra contrasts starkly with the generally accepted explanation for the origin of similar features in astronomical observations. Our experimental approach offers a powerful means to test and validate the computer codes used in X-ray astronomy. X-ray spectroscopy with an X-ray satellite is the main observational method to give information about compact objects, especially black holes. Black holes are indirectly studied by observing the X-ray continuum from a heated accretion disc and the X-ray fluorescence from the ambient gas of the stellar wind and the surface of a companion star in their binary systems. To derive physical properties from the observations, X-ray astronomers rely on non-local-thermodynamical-equilibrium (LTE) atomic physics in a cold ambient gas subject to an extreme radiation field, for which the mean radiation temperature is of the order of 1 keV. Theoretical models have been developed on the basis of the observed spectra 1-4 and complex computer codes were developed to analyse the observed X-ray spectra 12-16. The underlying assumption of these models is that the spectrum originates from a photoionized plasma. In other words, the intense radiation from the compact object photoionizes the gas, and generates a relatively low-electron-temperature highly ionized non-LTE plasma. However, laboratory experiments on non-LTE photoionized plasmas

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