An international research team led by the University of Vienna has achieved a major breakthrough. In a study recently published in Nature Astronomy, they describe how they made the first direct measurements of stellar wind in three Sun-like star systems. Using X-ray emission data obtained from the “astrospheres” of these stars using ESA's X-ray Multi-Mirror-Newton (XMM-Newton), they measured the rate of mass loss of these stars by stellar winds. Studying the co-evolution of stars and planets could aid in the search for life while also helping astronomers predict the future evolution of our solar system.
The research was led by Kristina G. Kislyakova, a senior scientist at the Institute of Astrophysics at the University of Vienna, deputy head of the Star and Planet Formation Group and main coordinator of the ERASMUS+ program. She was joined by other astrophysicists from the University of Vienna, the Laboratoire Atmosphères, Milieux, Observations Spatiales (LAMOS) at the Sorbonne University, the University of Leicester and the Johns Hopkins University Applied Physics Laboratory (JHUAPL).
Astrospheres are the analogues of our solar system's heliosphere, the outermost layer of our sun's atmosphere, which consists of hot plasma pushed into the interstellar medium (ISM) by solar winds. These winds drive many processes that cause the planet's atmosphere to escape into space (also known as atmospheric mass loss). Assuming that a planet's atmosphere is regularly renewed and/or has a protective magnetosphere, these winds can be the deciding factor in whether a planet becomes habitable or becomes a lifeless ball of rock.
Logarithmic scale of the solar system, heliosphere and interstellar medium (ISM). Image credit: NASA-JPL
While stellar winds are composed primarily of protons, electrons, and alpha particles, they also contain trace amounts of heavy ions and atomic nuclei such as carbon, nitrogen, oxygen, silicon, and even iron. Despite their importance in stellar and planetary evolution, the winds of Sun-like stars are notoriously difficult to contain. However, these heavier ions are known to capture electrons from neutral hydrogen that permeates the ISM, resulting in X-ray emissions. Using data from the XXM Newton mission, Kislyakova and her team discovered these emissions from other stars.
These were 70 Ophiuchi, Epsilon Eridani and 61 Cygni, three Sun-like main sequence stars located 16.6, 10,475 and 11.4 light-years from Earth, respectively. While 70 Ophiuchi and 61 Cygni are binary systems of two K-type (orange dwarf) stars, Epsilon Eridani is a single K-type star. By observing the spectral lines of the oxygen ions, they were able to directly quantify the total mass of stellar wind emitted by all three stars. For the three stars studied, they estimated the mass loss rates to be 66.5 ± 11.1, 15.6 ± 4.4, and 9.6 ± 4.1 times the Sun's mass loss rate, respectively.
In short, this means that the winds of these stars are much stronger than those of our Sun, which could be due to the stronger magnetic activity of these stars. As Kislyakova reported in a University of Vienna press release:
“In the solar system, solar wind charge exchange emission has been observed from planets, comets, and the heliosphere, providing a natural laboratory for studying the composition of the solar wind. Observing this emission from distant stars is much more difficult due to the weakness of the signal. In addition, due to the distance to the stars, it is very difficult to separate the signal emitted by the astrosphere from the actual X-ray emission of the star itself, part of which is “dispersed” across the field of view of the telescope due to instrumental effects.”
XMM-Newton X-ray image of the star 70 Ophiuchi (left) and the X-ray emission from the region surrounding the star (“annulus”), shown in a spectrum versus the energy of the X-ray photons (right). Photo credit: C: Kislyakova et al. (2024)
For their study, Kislyakova and her team also developed a new algorithm to disentangle the contributions of stars and their astrospheres to the emission spectra. This allowed them to detect charge exchange signals from the oxygen ions of the stellar wind and the neutral hydrogen in the surrounding ISM. This is the first time that X-ray charge exchange emissions from the extrasolar astrosphere have been directly detected. In addition, the mass loss rate estimates they derive could be used by astronomers as a benchmark for stellar wind models, expanding the limited observational evidence that exists for the winds of solar-like stars. As co-author Manuel Güdel, also from the University of Vienna, noted:
“Over three decades, there have been global efforts to substantiate the presence of winds around Sun-like stars and measure their strength, but so far only indirect evidence has suggested the existence of such winds based on their secondary effects on the star or its surroundings. “ Winds; Our group has previously tried to detect radio emissions from winds, but was only able to set upper limits on wind strength while not detecting the winds themselves. Our new X-ray-based results pave the way to directly find and even image these winds and study their interactions with surrounding planets.”
In the future, this method of direct detection of stellar winds will be facilitated by next-generation missions such as the European Athena mission. This mission will include a high-resolution X-ray Integral Field Unit Spectrometer (X-IFU), which Athena will use to resolve the finer structure and ratio of faint emission lines that are difficult to distinguish with XMM-Newton's instruments. This will provide a more detailed picture of the stellar winds and astrospheres of distant stars, helping astronomers constrain their potential habitability while improving models of solar evolution.
Further reading: University of Vienna, natural astronomy
Like this:
Is loading…
Comments are closed.