Lmst

#VicisAstro

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

#VicisAstro #wisskomm #astronomie #physik

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

#VicisAstro #wisskomm #astronomie #physik

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

#VicisAstro #wisskomm #astronomie #physik

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

Schwarz-weiß digitale Zeichnung: oben eine Katze in einer Katzenhängematte, die sich unter dem Gewicht der Katze verbiegt.

Unten 2-dimensional Folie als Raumzeit mit verschiedenen Gegegenständen drauf: die Sonne führt zur leichten Krümmung, ein Neutronenstern zu einer starken, bei einem Schwarzen Loch ist die Krümmung so stark, dass es außerhalb des Blatts reicht.

What did you always wonder about #BlackHoles? Something that you always wanted to ask an astronomer working on them?

Collecting questions for a reason, maybe even answering them in the comments (or at a later point).

#VicisAstro

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).

#astrodon #VicisArt #VicisAstro

My black and white and grey digital sketch of Cecilia Payne Gaposchkin. Above it, a citation from her thesis: 'The application of physics in the domain of astronomy constitutes a line of investigation that seems to possess almost unbounded possibilities'. Slightly in the background sketches of the energy levels in the hydrogen atom (orbital co-sketched) and a star with sun spots and loop/protuberances. Name and citation underlines in red, everything else is black and white.

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

Fully digitally hand-drawn slide showing sketches of the #XRISM and #Athena X-ray telescopes and listing the three bullet points for what's next explained in the post.

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

Fully digitally hand-drawn slide first showing a broadband spectrum with three X-ray "photometric" bands. Then another showing how to turn the photometry into "colors" and that we expect a certain parts on such a color-color diagram when absorption of the X-ray spectrum changes.

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

Fully digitally handdrawn slide shiwing three graphs, one of a simulated absorption lightcurve (think random up and down), with typical timescales and absorption variability indicated, one of the an autocorrelation function of the lightcurve, with typical timescale indicated as the point where the autocorrelation falls to 0.5, and one of clump radius vs. mass where it's indicated that given absortion variabilities have clear locations in these plots.

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

Fully-handdrawn slide showing two different line of sight through the wind of a high mass X-ray binary, one passing closer to the start through denser wind and one further out. There are also two stick figures, one drowning under the bullet points for what the short term variability depends on (as described in the toot), another one below it with a lamp above it's head thinking "simulate"

That's why a few years ago - well, more like 5 or 6 by now - a few of us (including @fuerst and @pkretsch) started the X-Wind collaboration, aiming to bring together X-ray astronomers and experts in winds from massive stars from other wavelength & from theory in order to better understand winds in HMXBs: https://www.sternwarte.uni-erlangen.de/~grinberg/x-wind/

#VicisAstro
7/11

A fully hand-drawn slide showing five faces with names and the title "X-Wind collaboration"

Why study HMXBs? They are key sources that touch all kind of astro areas (high energy, stellar, accretion physics) + we can often use data taken for other purposes to study the winds (absorption is noise for accretion physics studies).

They are systems where one supernova has happened & another will and are progenitors for gravitational wave events. We also want to know about accretion history of HMXBs (their total energy output) & use them as unique labs for complex physics.

#VicisAstro
6/11

Fully handdrawn slide showing a supernova explosion and a binary black hole merger with arrows pointing towards the word "HMXB".

2. Looking at high resolution spectra at low X-ray energies where there are many line transitions from different ions, we can see narrow features (lines, RRC) imprinted in absorption or emission onto the continuum.

This gives us information about properties of the wind material such as ionization level and sometimes process, temperature, composition etc.

Example studies: https://ui.adsabs.harvard.edu/abs/2017A%26A...608A.143G/abstract & https://ui.adsabs.harvard.edu/abs/2020A%26A...641A.144L/abstract & https://ui.adsabs.harvard.edu/abs/2021A%26A...648A.105A/abstract

#VicisAstro
5/11

Fully hand-drawn slide showing the sketch of high resolution 2-3 keV spectrum for a black hole without intervening stellar wind and with X-rays passing through stellar wind. In one case, the spectrum normalized to the continuum is flat, in the second there are a lot of narrow absorption and emission features.

There are two main ways how we can observe the effects of the wind on the X-rays.

1. looking at broadband energy spectra (say in the 1-100 keV range), we see increased overall absorption, seen as additional decline in soft X-rays in HMXBs vs. source where we can more directly look onto the compact object, without the intervening wind material.

This gives us information about the total amount of wind material along the line of sight.

Example study: https://ui.adsabs.harvard.edu/abs/2015A%26A...576A.117G/abstract

#VicisAstro
4/11

Fully hand-drawn slide showing the sketch of a 1-100 keV spectrum for a black hole without intervening stellar wind and with X-rays passing through stellar wind. In one case, the spectrum has the shape of a power low that is slightly affected at low energies by absorption in the interstellar medium. In the second case, there is strong additional absorption at low energies, due to the stellar wind.

Luckily, nature gave us High Mass X-ray Binaries (HMXB), where a black hole or neutron star (short: compact object) is close to an O/B star & accretes matter from its wind. The accretion process leads to production of high energy radiation.

These X-rays then pass through the remaining wind and can be used as a "backlight" to probe individual wind clumps & overall wind structure. To do so, we need to observe the X-rays with space-based X-ray telescopes, such as XMM-Newton.

#VicisAstro
3/11

Fully hand-drawn slide showing a high mass X-ray binary with X-ray emitted close to a compact object that is deeply embedded in the wind of an O/B star companion and being observed by an X-ray telescope.

O/B supergiants are the "superstars" of the Universe: they have much higher temperature & luminosity than our sun (& higher mass).

They live short & bright lives during which they can loose up to one hundred-thousandth of mass per year through winds. That's a VERY high mass loss and strongly influences how these stars develop and interact with their environment.

Yet, we struggle understanding these winds because their clumpy structure is hard to study in single stars.

#VicisAstro
2/11

Fully hand-drawn digital slide showing a drawing of a Hertzsprung-Russel diagram and a sketch of a O/B supergiant star.

Want to know what my research is about? Follow this thread 🧵 based on a 10min talk I've drawn for a meeting.

The talk was aimed at non-specialist space science colleagues (not the general public!). The slides were built up step by step, but I'm omitting this here & showing only the final graphs, less this becomes a 34-part thread. 11 is plenty enough!

So: "Understanding Winds of Massive Stars Using High Mass X-ray Binaries"

#astrodon #XraysAreTheBestRays #SciArt #scicomm #VicisAstro
1/11

Title slide of the talk, fully digitally hand-drawn showing a sketch of a massive star with a clumpy stellar wind, a black hole with X-ray emitted from close to it deep within the wind, the XMM-Newton X-ray telescope observing it and a small self-portrait of the speaker = me. The title of the talk is "Uderstanding Winds of massive stars using high mass X-ray binaries"

Cecilia Payne-Gaposchkin, who revolutionized our understanding of what stars & the Universe are made of, was born #OTD in 1900.

In 1926, she wrote what is considered the "undoubtedly most brilliant PhD thesis ever written in astronomy".

She continued in the same spirit - only to be denied a professorship (or even the a proper astronomer position). She finally became a professor at Harvard at 1956(!) & first woman to chair a department.

#VicisAstro #astronomy #WomenInSTEM #astrophysics #SciArt

So what kinds of black holes are actually out there?

#BlackHoleWeek #BlackHoles #VicisAstro #sciart #scicomm

A sketchnote with white lines/text on a dark dotted paper background, made by me.

First text block: Black holes = objects with gravitational pull so strong that nothing, not even light, can escape itLeft: A 2D sketch of spacetime around black hole (funnel like)Right: a sketch of the accretion disk around a black hole, including light bending.Two more text blocks in between:First textblock:There are two kinds of confirmed black holes:1. stellar mass black holes with a few to a few dozen solar masses are the remnants of massive stars which used up all their nuclear fuel2. supermassive black holes with millions to billions solar masses lurk in the centers of galaxiesSecond textblock:Maybes are:3. intermediate mass black holes in the centers of globular clusters or in ULX (ultraluminous X-ray sources)4. primordial black holes created shortly after the Big Bang

#papertime 🥳

Where we use a method originally used for AGN to answer the question whether
we can use variability in individual X-ray lines to probe the variable stellar wind.

And the answer is: yes, we can!

The paper (submitted not yet refereed) is:

"Stellar wind variability in Cygnus X-1 from high-resolution excess
variance spectroscopy with Chandra" by Härer et al.
https://arxiv.org/abs/2304.14201

Let me disentangle what the title means: 1/6

#astrodon #BlackHole #VicisAstro #astronomy #SciArt

#VicisAstro

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