A giant cosmic funnel sucks in gas from its surroundings. But not all of that gas falls in — some is spat back out, like splashes from boiling water. That's exactly what the ultraluminous X-ray source NGC 5204 X-1 does: a compact object (likely a black hole) feeds so voraciously that the excess escapes in powerful jets.
Using the RGS spectrometer on XMM-Newton, astronomers split the source's X-ray light into its component colors, much as a prism breaks up sunlight. In the spectrum, they spotted lines from gas moving both toward us and away from us. This tells us the outflow takes the shape of two cones spreading in opposite directions, like twin lighthouse beams.
Beyond the fast jets, the team also examined slower gas. From oxygen lines, they pinned down its density: roughly 10 billion particles per cubic centimeter (by comparison, Earth's atmosphere at the surface has about a million times more). The temperature of this gas is at least 150,000 degrees. It turns out that both particle collisions and radiation from the black hole itself influence the gas's ionization — a 'hybrid' regime that hasn't always been taken into account before.
as written by the authors arXiv:2603.11922
Ultraluminous X-ray sources (ULXs) are non-nuclear X-ray binary systems that exceed the Eddington luminosity for a 10 Msun black hole. The majority of these sources are thought to be stellar-mass compact objects accreting at super-Eddington rates, exhibiting powerful relativistic winds. These winds have been identified through the detection of absorption lines with a blueshift as high as 0.3c and emission lines typically found at their laboratory wavelengths. In this work, we analysed the XMM-Newton data of the ULX NGC 5204 X-1, which has been observed to exhibit emission lines with a blueshift of about 0.3c. The aim of this study is to examine the geometry and physical properties of the accretion disc and the relativistic outflows. In addition, we aim to explore the factors that influence the ULX spectral transitions. We undertook an observing campaign with XMM-Newton to explore the source behaviour at different luminosities. In this first paper of the series, we performed high-resolution X-ray spectroscopy, including archival data, with the RGS instrument which allowed us to resolve both emission and absorption lines. The outflows features were characterised using physical models of plasma in collisional-ionisation and photoionisation equilibrium. We identify collisionally-ionised blueshifted and redshifted components at about 0.3c. These findings have high statistical significance and suggest a biconical structure for the outflow. Additionally, the analysis of the O VII line triplet observed in the spectrum enables us to infer physical properties of the low-velocity line-emitting plasma, e.g. electron density (ne $$\sim 10^{10}$$ cm$$^{-3}$$) and temperature (Te $$ \geq 1.5 \times 10^5$$ K). A hybrid plasma whose ionisation balance is affected by both collisions and radiation is favoured.
Ultraluminous X-ray sources shine hundreds of times brighter than 'ordinary' black holes of the same mass — hence the 'ultraluminous' in their name.