How does the understanding for the size of the world change one's thinking?
What was it like living on the Easter Island, the world a place you can walk around within a few days?
When Einstein developed general relativity, we did not know there were other galaxies beyond the Milky Way.
Most people today don't know how vast the Universe - and yet my own thinking is deeply shaped by being an astrophysicist, by the fact that we are just a tiny memory of a speckle of dust.
Trotzdem ist das Bild der Folie hilfreich, zum Beispiel im Gravitationslinsen zu verstehen (gravitationsbedingte Lichtablenkuig) oder warum Licht aus der unmittelbaren Nähe eines Neutronensterns oder Schwarzen Lochs rotveschoben bei uns ankommt. Wenn das Bild aber zusammen bricht, ist es kein Beweis, dass die Relativitätstheorie falsch ist. Nur dass unser Bild Unzulänglichkeiten hat. 4/4
Gravitationslinsen: https://www.esa.int/ESA_Multimedia/Images/2025/03/Strong_gravitational_lenses_captured_by_Euclid
Allerdings sind solche Modelle & Vergleiche aus unserem Alltag auch gefährlich: Sie sind keine vollständige Beschreibung der Wirklichkeit, das geht nur mit der Mathematik. Auch brechen sie recht einfach zusammen - es gibt z.B. keine unendlich dehnbare Folie. Manchmal können sie auch irreführend sein: bei einer Folie gibt es 2 Seiten, weil sie in einen 3dimensionalen Raum eingebettet ist. Das ist bei der vierdimensionalen Raumzeit nicht der Fall. 3/4
Zumindest ich kann die Raumzeit um ein Schwarzes Loch berechnen, mir aber keine vier Dimensionen vorstellen. Ein solches Modell hilft mir, die Mathematik in Bilder (und Cartoons) zu übersetzen. Die Mathematik ist die Sprache der Physik, aber ohne viel entsprechendes Training lässt sich diese Sprache nicht verstehen. Gut, dass es Wissenschaftskommunikator*innen als Übersetzer*innen gibt! 2/4
Gedanken zu Wissenschaftskommunikation & (Wort-)Bildern aus meinem Buch:
Wir Physiker*innen verwenden gerne Vergleiche aus dem Alltag: ob nun die Raumzeit als eine dünne Folie (oder Katzenhängematte 😺) oder das sich ausdehnende Universum mit Galaxien drin als Rosinenbrot. Solche Modelle vereinfachen physikalische/mathematische Zusammenhänge, so dass wir uns die wesentlichen Eigenschaften besonders einfach vorstellen können. 1/4
#VicisAstro #wisskomm #astronomie #physik #CatsOfMastodon #SciArt
It's only since Cecilia Payne's PhD thesis in 1925, that we know what the stars - and our Sun - are made of: mostly hydrogen.
Her thesis was described as ""the most brilliant PhD thesis ever written in astronomy" and it extremely readable: https://ui.adsabs.harvard.edu/abs/1925PhDT.........1P/abstract
Yet It took until 1956, 10 years before her retirement, for her to become full professor - because women were barred from becoming full professors at Harvard.
(Posted because she was born #OTD).
What next for this research?
1. Apply methods to more sources! Also to build a sample and test different star & binary properties e.g. https://ui.adsabs.harvard.edu/abs/2023A%26A...674A.147D/abstract & https://ui.adsabs.harvard.edu/abs/2021MNRAS.501.5646M/abstract
2. Refine methods (better statistics tools, take more effects into account ...) - e.g. https://ui.adsabs.harvard.edu/abs/2023arXiv230414201H/abstract
3. And of course we hope for better data with #XRISM and #Athena missions!
#VicisAstro #XraysAreTheBestRays #SciArt #scicomm #wisskomm #VicisArt
11/11
High-mass X-ray binaries (HMXBs) offer a unique opportunity to investigate accretion onto compact objects and the wind structure in massive stars. A key source for such studies is the bright neutron star HMXB Vela X-1 whose convenient physical and orbital parameters facilitate analyses and in particular enable studies of the wind structure in HMXBs. Here, we analyse simultaneous XMM-Newton and NuSTAR observations at ϕ<SUB>orb</SUB> ≈ 0.36-0.52 and perform time-resolved spectral analysis down to the pulse period of the neutron star based on our previous NuSTAR-only results. For the first time, we are able to trace the onset of the wakes in a broad 0.5-78 keV range with a high-time resolution of ~283 s and compare our results with theoretical predictions. We observe a clear rise in the absorption column density of the stellar wind N<SUB>H,1</SUB> starting at orbital phase ~0.44, corresponding to the wake structure entering our line of sight towards the neutron star, together with local extrema throughout the observation, which are possibly associated with clumps or other structures in the wind. Periods of high absorption reveal the presence of multiple fluorescent emission lines of highly ionised species, mainly in the soft-X-ray band between 0.5 and 4 keV, indicating photoionisation of the wind.
What we want are measurements of how absorption changes with time as clumps pass through our line of sight towards the compact object.
The usual way is to use spectral modelling - this allows exact measurements but needs long exposures. Bad for time resolution!
Instead, we can use colors. They need short exposures, but are noisy & harder to model. I did develop an approach how to make use of the typical patterns in color space to do so: https://ui.adsabs.harvard.edu/abs/2020A%26A...643A.109G/abstract
#VicisAstro
10/11
High mass X-ray binaries hold the promise of allowing us to understand the structure of the winds of their supermassive companion stars by using the emission from the compact object as a backlight to evaluate the variable absorption in the structured stellar wind. The wind along the line of sight can change on timescales as short as minutes and below. However, such short timescales are not available for the direct measurement of absorption through X-ray spectroscopy with the current generation of X-ray telescopes. In this paper, we demonstrate the usability of color-color diagrams for assessing the variable absorption in wind accreting high mass X-ray binary systems. We employ partial covering models to describe the spectral shape of high mass X-ray binaries and assess the implication of different absorbers and their variability on the shape of color-color tracks. We show that in taking into account, the ionization of the absorber, and in particular accounting for the variation of ionization with absorption depth, is crucial to describe the observed behavior well.
We simulate "absorption light curves", i.e. measurement of how much material is along the line of sight. Such lightcurves have two main properties: a typical timescale and a typical absorption variability.
We can get the typical timescales from the autocorrelation function and it's a good estimate for the clump radius. If we can measure absorption variability, we can then also get clump muss. But how measure that?
#VicisAstro
9/11
The problem is that the winds are complex and clumpiness and with them short-term variability we observe depends on e.g. line of sight, clump properties such as mass and radius, clump movement, wind ionisiation ... Enough parameters to feel totally lost and drowning!
So what I've done with my amazing colleague I. El Mellah is to try to disentangle a part of this complexity via simulations!
Careful, we'll now be diving into this rather complex paper: https://ui.adsabs.harvard.edu/abs/2020A%26A...643A...9E/abstract
#VicisAstro
8/11
Context. In high mass X-ray binaries, an accreting compact object orbits a high mass star, which loses mass through a dense and inhomogeneous wind. <BR /> Aims: Using the compact object as an X-ray backlight, the time variability of the absorbing column density in the wind can be exploited in order to shed light on the micro-structure of the wind and obtain unbiased stellar mass-loss rates for high mass stars. <BR /> Methods: We developed a simplified representation of the stellar wind where all the matter is gathered in spherical "clumps" that are radially advected away from the star. This model enables us to explore the connections between the stochastic properties of the wind and the variability of the column density for a comprehensive set of parameters related to the orbit and to the wind micro-structure, such as the size of the clumps and their individual mass. In particular, we focus on the evolution with the orbital phase of the standard deviation of the column density and of the characteristic duration of enhanced absorption episodes. Using the porosity length, we derive analytical predictions and compare them to the standard deviations and coherence time scales that were obtained. <BR /> Results: We identified the favorable systems and orbital phases to determine the wind micro-structure. The coherence time scale of the column density is shown to be the self-crossing time of a single clump in front of the compact object. We thus provide a procedure to get accurate measurements of the size and of the mass of the clumps, purely based on the observable time variability of the column density. <BR /> Conclusions: The coherence time scale grants direct access to the size of the clumps, while their mass can be deduced separately from the amplitude of the variability. We further show how monitoring the variability at superior conjunctions can probe the onset of the clump-forming region above the stellar photosphere. If the high column density variations in some high mass X-ray binaries are due to unaccreted clumps which are passing by the line-of-sight, this would require high mass clumps to reproduce the observed peak-to-peak amplitude and coherence time scales. These clump properties are marginally compatible with the ones derived from radiative-hydrodynamics simulations. Alternatively, the following components could contribute to the variability of the column density: larger orbital scale structures produced by a mechanism that has yet to be identified or a dense environment in the immediate vicinity of the accretor, such as an accretion disk, an outflow, or a spherical shell surrounding the magnetosphere of the accreting neutron star.
Dr. Victoria Grinberg