8minutesold.bsky.social
Astrophysicist studying cosmic choreographies of dwarf galaxies. Junior Research Group Leader at AIP, Street Photographer (he/him)
Autor des Buchs „Von tanzenden Galaxien, Dunkler Materie, und anderen kosmischen Rätseln“
Potsdam, Germany
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What I especially like is that it’s an award for the group, not individuals. Which is much more representative of what science 🧪 and astronomy 🔭 in particular is actually like.
So this is all thanks to my fantastic team and the great wider environment provided for us at the @aippotsdam.bsky.social
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Thanks!
Haha, yeah, it’s a joke I like to make when talking about MOND in German. Even put “Mond” next to “MOND” in the glossary of my book, against the advice of my lector who realized I don’t really talk about the moon at all. 😅
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Call it a new trend. After “fast fashion”, the time is ripe for “tired fashion”.
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In light of proper motion errors, distance errors and range of possible MW potential, orbit integrations are in fact expected to show a widening of a satellite plane even for an intrinsically stable plane with constant width.
One thus can't infer that the observed MW satellite plane is unstable.
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Uncertainties in satellite distance and adopting incorrect host potentials also contribute noticeably to the widening (and thus inferred, ostensible instability). Using identical distance+proper motion errors but making them correlated (more distant sats have higher errors) makes things even worse!
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Thus, even though we know that the intrinsic satellite planes in our models are stable, we'd infer them to be unstable if based on the ostensible, apparent widening when backward-integrating.
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We set up stable satellite planes, integrate them forward in a defined host potential (black line, flattening remains constant), "mock-observe" them by adding realistic proper motion uncertainties, and integrate backwards (green lines). Result: even small errors result in a significant widening.
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We now ask: can you actually infer this? After all, measurements of the 3D motion of satellites come with uncertainties. And adding errors to a highly correlated system will disperse things.
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Many Milky Way satellite galaxies are part of and co-orbit in a flattened structure. This plane of satellites challenges cosmology. Yet, some recent papers have integrate the satellite orbits backwards, found that their distribution widens, and argued that this means that the plane is not stable.
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There are a lot more dwarfs orbiting our Milky Way, and we now even get good measurements of the motions of dwarf satellite galaxies around our neighboring Andromeda galaxy. Lots of exciting developments in this field.
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Haha, that’d be awesome … except for my non existent musical talent. 😅
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Unfortunately, it lost its funding and is now supported by a company providing Astro-related software (thus excluded from grants). The town didn’t fare well after reunification either (economically+politically). But the museum and its team are fantastic, super dedicated and definitely worth a visit!
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There’s a lot of history that left an imprint at the observatory. Started before WWII, used for weather observations during the war, continued astronomy under Soviet occupation but lost many instruments, was associated to @aippotsdam.bsky.social precursor institutes a couple times.
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I also saw the library and their original bibliographic catalogue on variable stars. Each star got a card, and whenever a new publication mentioned it the reference was added to the card. This was maintained into the 1990s, got digitized and became part of the Strasbourg Astronomical Data Center.
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Consequently, it has one of the biggest archives of photographic plates, several 100k in total. With a smart filling system in which the position along the shelve corresponds to right ascension and height in the shelve to declination (and then year of observation). 85% of these have been digitized.
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The observatory’s main activity were two long-term photographic surveys, monitoring the whole visible sky and select fields whenever possible. These were used to identify variable stars, with about 11000 (a quarter of all known ones) discovered in Sonneberg.
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Back then the city seems to have had the money. It used to be a center of toy production, evidence of which can still be found in the fact that it hosts the German Toy Museum. They also produced and exported lots of Christmas decorations, with Woolworth building a major warehouse right in the city.
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Turns out they are celebrating their 100 year anniversary this year. They were founded as a municipal observatory (!), upon an initiative by local astronomer Cuno Hoffmeister, by the city of Sonneberg.
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Here is a longer video explanation of this work, illustrating the peculiarly lopsided satellite galaxy system of the Andromeda galaxy. 🧪🔭
youtu.be/xO7rTu5ADwQ?...
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If course there are infinite possibilities then, and thus one could always find something that sticks out. But as I tried to argue before, we didn’t set out to search for a weird feature,but focus on one that is established and rather fundamental.
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Of course there can be many more properties, which I think is the point Michael wants to make. To stick with the balls, that’s like suggesting to not only look for color, but also whether a ball is too big, of a different material, less massive, in fact a cube not a ball, or whatever.
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Though the analogy is limited because we need a base comparison model (isotropy in our case) to compare both the observed and simulated systems against. We need that to define what we call the isotropic frequency, which essentially quantifies the „unlikeliness“ of a given system.
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In Michael‘s example with the balls, this would count all cases of oddly-colored balls as similarly rare. So if there are 20 single balls each with a different color and 80 red ones, observing e.g. a purple one would result in a simulation analog frequency of 20%. We wouldn’t call that a challenge.
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Yes that’s what we try here. Generalize the property we investigate (asymmetry) by quantifying it via how rare a given arrangement is for an isotropic model. We then test how often similarly rare systems are found in sims; no requiring a specific arrangement, just having the same isotropic frequency
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So now we tested whether the known lopsidedness in M31, which is remarkable if you compare it to isotropy, is also special compared to cosmological expectations. We could have found that such an arrangement is common in the simulations, and would have reported that. But it turns out it isn’t.
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Furthermore, lopsidedness is a quite active field and was already studied independently of this work for external galaxies for years. Both @cosmicwebmaster.bsky.social and I published on it, in fact in 2017 I showed that for stacked satellite systems, there does not seem to be any tension with LCDM.
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Thanks for your explanation, but I have to disagree. We didn’t pick a weirdness to ensure that we find a disagreement with LCDM.
For one, a global asymmetry is a much more fundamental quality than other „weirdnesses“ you suggest, like a distribution in a triangle.
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That’s a bit harsh given that we account for this look-elsewhere effect: we don’t just search for similarly asymmetric distributions in the simulations, but for ones that are similarly unlikely compared to an isotopic one. See this paragraph and the following ones, and Fig 5.
🧪🔭