Low-mass X-ray binaries (LMXB) consist of a neutron star or black hole accreting material from a star similar to our Sun. Most accretion happens during violent eruptions where the LMXB system lights up drastically. Simultaneously, some of the material that spirals in is moved back into space in the form of disc winds and jets.
Warm gas is the most common sign of outflowing material. Only “hot” or “cold” gas winds have been observed in transient X-ray binaries until now.
Astronomers using the most powerful telescopes on Earth and in space, a team of astronomers has found for the first-time blasts of hot, warm, and cold winds from a neutron star while it consumes matter from a nearby star. In this study- led by the University of Southampton, astronomers studied the recent eruption of the X-ray binary known as Swift J1858.
They found repeated signatures of a warm wind at ultraviolet wavelengths. These signatures were occurring simultaneously as signatures of cold wind at optical wavelengths.
This is the first time that astronomers have observed winds from such a system across different electromagnetic spectrum bands. For this study, astronomers used a combination of telescopes, including NASA’s Hubble Space Telescope (HST), the European Space Agency’s XMM-Newton satellite, the European Southern Observatory Organisation’s Very Large Telescope (VLT), and the Spanish Gran Telescopio Canarias (GTC).
Lead author Dr. Noel Castro Segura of the University of Southampton said: “Eruptions like this are rare, and each of them is unique. Normally they are heavily obscured by interstellar dust, which makes observing them difficult. Swift J1858 was special because even though it is located on the other side of our galaxy, the obscuration was small enough to allow for a full multiwavelength study.”
Co-Author Dr. Hernández Santisteban from the University of St Andrews said, “Only one other system — the black hole X-ray binary, V404 Cyg — has shown similar properties. However, our attempt to perform the same experiment on that system was unsuccessful because the eruption ended before we could get the ground-based and space-based telescopes to observe it simultaneously.”
Dr. Castro Segura continued, “All the astronomers in the field were incredibly excited, to the point that we combined our efforts to cover the full spectrum, from radio to X-ray using state-of-art observatories on Earth and in space.”
Co-author Nathalie Degenaar from the University of Amsterdam added, “Neutron stars have a powerful gravitational pull that allows them to gobble up gas from other stars. The stellar cannibals are, however, messy eaters, and much of the gas that neutron stars pull towards them is not consumed but flung into space at high speed. This behavior has a large impact on the neutron star itself and its immediate surroundings. In this paper, we report on a discovery that provides key information about the messy eating patterns of these cosmic cookie monsters.”
“This time, we had cosmic luck on our side, as we were able to co-ordinate ten telescopes and point them towards the J1858, all while it was fully active. This allows us to obtain much more information since we can use different techniques at different wavelengths,” Dr. Hernández Santisteban said.
Dr. Degenaar added, “Designing such an ambitious observing campaign – built around the best telescopes on Earth and in space – was a huge challenge. So, it is incredibly exciting that all this work has paid off and allowed us to make a key discovery that would not have been possible otherwise.”
Along with identifying different winds, the team also determined the temporal evolution of the gas that flows out. They found that the substantial variations in the system’s brightness do not significantly impact a warm wind.
Dr. Castro Segura said, “In this research, we combined the unique capabilities of the HST with the best ground-based telescopes, such as the VLT and GTC, to obtain a complete picture of the dynamics of the gas in the system, from the near-infrared to ultraviolet wavelengths. This allowed us to unveil for the first time the true nature of these powerful outflows.”
“The new insights provided by our results are key to understanding how these objects interact with their environment. By shedding energy and matter into the galaxy, they contribute to the formation of new generations of stars and to the evolution of the galaxy itself.”
- Castro Segura, N., Knigge, C., Long, K.S. et al. A persistent ultraviolet outflow from an accreting neutron star binary transient. Nature 603, 52–57 (2022). DOI: 10.1038/s41586-021-04324-2