John Forbes

@redshiftless.bsky.social

1438 Followers 1566 Following

Astronomer in Aotearoa/New Zealand at the University of Canterbury. Pusher of pixels, pens, arrays, and computer keys. www.johncforbes.com

The speed distributions of quasi-interstellar objects as they re-encounter the Solar System (Figure 6 of the paper). The purple lines are the most realistic, and they peak at velocities around 0.1 km/s (barely unbound from the Solar System).
Figure 5 of the paper. Here's the corresponding caption: "Predicted quasi-ISO rates. The y-axis shows our predictions for the present-day rate of quasi-ISOs entering the inner Solar system (pericenters < 5 au), compared against the number of Oort cloud objects ejected over the past 500 Myr. Each set of colored points corresponds to a different heating+ejection model, while the different symbols correspond to Oort cloud erosion models. N23 refers to the simulation results from D. Nesvorn´y et al. (2023). In the case of “ejection timing only” we use the times that particles from the simulation cross the 500k au sphere in the simulation to interpolate the results of our burst simulations. In “last 100 Myr + kin” we initialize each particle with its position and velocity at the given time, integrate it, and evaluate the rate based on the resulting particle distribution. The filled vs hollow points correspond to different assumptions about the normalization of the Oort cloud, respectively one based on the ISO density, and one based on the rate of long-period comets. Changes in normalization move points parallel to the solid line (increasing the number of objects ejected directly increases the rate of quasi-ISOs). The rate required to expect one detection in a 10-year survey is of order 10^−1 /yr, neglecting observational efficiencies."
An animation in 3D with axes labelled Delta x, Delta y, and Delta z (pc). There is a yellow star in the centre with a sphere around it represented by a few great circles. Particles start travelling away from that sphere at t=4400 Myr (shown in the corner). The time ticks up and the particles in purple start curving back towards the sphere. When they hit the sphere, the particle and its purple tail (showing its trajectory) turn black and freeze. Another set of faint grey lines steadily move away and don't return. A makeshift arrow in the corner of the plot shows the peculiar velocity vector, the motion of the Sun relative to its surroundings. The movie stops at t=4500 Myr, then rotates around showing that there's some nontrivial structure in the returning orbits.
Londo Mollari, the Centauri ambassador to Babylon 5, played by Peter Jurasik. In the photo a man in a fancy uniform raises a glass, likely giving a toast, with plants and a irregular set of blue neon lights in the background. His hair is arranged such that the front half of his head is bald, then about 10 cm of hair fans outward perpendicular from his head, in a manner somewhat reminiscent of a trifoil hat worn with one point at the back of the head.
A graph! x-axis is years 2018-2026.3; y-axis is log-scaled "Captures per day" referring to photos/videos taken by my phone. A very noisy blue dataset labelled "daily" is shown, along with a 30-day mean, shown in orange. 3 events associated with step changes in the capture rate are shown - "Adopted Cats" late 2020, "Kid born" mid-2022, and "Kid discovers he can take photos on phone" this past week.
The meme of Angela Kinsey appearing quietly behind Dwight Shrute from the Office (US). In the first panel, Dwight is enjoying something, and is captioned "READING THE DEMON HAUNTED WORLD". Angela is labelled "MENTION OF THE 1974 NOBEL PRIZE WITH NO ACKNOWLEDGEMENT OF BELL". In the second panel, Dwight sees Angela and is surprised, captioned "F**k"
Figure 3 from the paper. It's a version of the cartoon diagram shown elsewhere in the thread, but made with numerical stellar models. Each model is coloured by its fate, with longer frozen core timescales corresponding to yellower colours, and shorter corresponding to bright pink. The closer the objects end up in this space to a particular locus of points (not shown) where Lnuc=Lsurf, the longer the frozen core lasts.
Figure 1 from the paper, showing how the erstwhile brown dwarfs evolve. The coloured arrows represent the paths the different stellar and substellar objects take as they evolve on a plot of mass against ψ, the thermal energy per particle in units of the Fermi energy in the star’s core. Lower values of ψ indicate colder and more degenerate cores. The separately coloured regions and their corresponding outline arrows indicate what direction an object would move. In the pink region within the parabola, objects have a nuclear luminosity, Lnuc, greater than their surface luminosity, Lsurf and they evolve to the right as their cores heat up. In the blue region, Lsurf > Lnuc, so objects evolve to the left as they radiate more energy than they generate. The black parabola is where Lnuc = Lsurf . The solid right-hand side of the parabola represents the main sequence; it is stable to perturbations in ψ. The dashed left-hand side is unstable. The lowest mass on the parabola is the hydrogen burning limit, MHBL. The arrows for the red dwarf and brown dwarf are horizontal as these objects do not change their mass throughout their lives without an outside influence. Maroon, pink, and beige dwarfs begin as brown dwarfs and evolve leftwards until an episode of mass accretion results in them splitting off from the brown dwarf arrow vertically, at least in the case of fast accretion. When accretion has stopped, they then evolve horizontally to the left or right. Maroon dwarfs, like red dwarfs, evolve left and settle on the main sequence. Beige dwarfs end up above the hydrogen burning limit, but outside of the parabola, and so evolve left like a brown dwarf, never reaching the main sequence. A pink dwarf is located inside the parabola when mass has stopped accreting and then evolves to the right to settle on the main sequence. The ‘frozen cores/plateaus’ region in the parabola is the area in which a subset of our pink dwarf models have a frozen core or luminosity plateau
Meme of a guy in a red uniform shirt sweating and deciding between several buttons. The guy has a brown circle obscuring his face and is captioned "Brown Dwarf Gaining Mass". There are three buttons labeled "Pink", "Beige", and "Maroon"
A text meme. 1. Be a brown dwarf 2. Add mass 3. ?????? 4. (strikethrough: Profit) Become a star!
An artist's impression of a brown dwarf, from NASA/JPL-Caltech.
The figure from the linked paper (three panels, each a plot of some quantity vs time in days). Here's an expanded verision of the corresponding caption: Non-gravitational accelerations (NGAs) and their corresponding mass loss rates. Top panel: Non-gravitational acceleration from the JPL Small-Body Database or the final line of Table 1 in T. M. Eubanks et al. (2025). Reported errorbars are shown, and extrapolations into the future or prior to October are shown as dashed lines. The figure shows 5 lines, converging on an acceleration of order 10^-8 au per day^2 for 3I/ATLAS. Middle Panel: NGAs from the top panel are translated into mass loss rates assuming 1 km diameters, with ζ = 0.5 and ρ = 0.5 g cm^−3. Additionally the JPL Dec 17 solution for other diameters (0.5 km and 2 km) are shown as dotted lines. Data points are from JWST (M. A. Cordiner et al. 2025), SPHEREx (C. M. Lisse et al. 2025), ALMA (N. X. Roth et al. 2025), TRAPPIST-North (E. Jehin et al. 2025), and Swift (Z. Xing et al. 2025). The plot shows a variety of data points scattered around the lines, mostly of order 10^4-10^5 g/s, with the 1 km curves passing close to the data points that measure CO2, and mostly above the other datapoints, depending on the model. Bottom Panel: CO2 production rates measured by JWST are treated as upper and lower limits, and observations where CO2 is inaccessible are shown as lower limits. Given these constraints, the range of Mdot values and hence diameters for two different reported NGA solutions is shown. The JPL solution is unable to simultaneously fit the upper limit from JWST and the lower limit from TRAPPIST-North. The plot shows the same thing as the middle panel, but with some additional interpretation, namely that some points should be considered upper limits and some lower limits. A red shaded region labelled Eubanks+ Accel shows a range of diameters from 820 to 1050 meters. A gray region labeled JPL Accel shows a diameter of 1100 m.
A long queue of people waiting in a queue on a footpath next to a grassy river bank with various interesting plants, at the Ōtautahi botanical garden. A sign in the foreground directs people in various directions, but the labels are cut off.
A screenshot of text, headed "Description" followed by a paragraph "XBIGSpace is an independent, fan-made channel with no official affiliation with NASA, SpaceX, or any related organizations. Our content is inspired by publicly available scientific discussions, documentaries, and space research - reimagined purely for educational and inspirational purposes." New paragraph: "All narration is delivered using AI-synthesized voice, and does not represent any real individual."
A printed sign on a wooden planter with grass in the foreground and long thin green leaves in the planter. The sign says “RCG compost project; in progress; please leave”
A screenshot of the top of a wikipedia page for "Why We're Polarized", the book by Ezra Klein. In the screenshot, the start of the second paragraph of the article is highlighted, "Opinion on the book is polarized"
A screenshot of a google search result for "2*pi*(8 kpc)/(220 km/s)" which is roughly the time it takes the Sun to go around the Galaxy. In the screenshot, google's calculator has popped up and parsed the expression correctly, but then returns the result 3 899 243.9 years, and answer which is off by 2 orders of magnitude.
A screenshot from a livestream filmed with an infrared camera in grayscale, showing a sleeping adult ferret in a container on a bed of paper squares(?) with an indeterminate number of ferret kits (turns out there are 8!)
A screenshot from the Aurora app showing KP forecasts as a function of time: Now: 3.0 1800: 4.0 2100: 3.67 Midnight: 7.67 0300: 7.67 0600: 7.33
An image of Claudius Ptolemy, overlaid with a bust of Ptolemy in the outline of a heart. The bust has a thought bubble with the word epicycle. Several pink hearts as well as a diagram of the motions of planets in a geocentric epicycle+defferent system are also shown. Overlaid in several bold fonts are the words “RIP claudius ptolemy you wouldve loved john forbes :(“
The Inglourious Basterds meme in which a man holds up 3 fingers in such a way that he is outed to the Germans as a non-German.
A screen capture of Sir Alec Guinness in his role as Obiwan Kenobi in Star Wars Episode IV: A New Hope. His character is saying around this point in the movie "Now that's a name I've not heard in a long time."
A photo of a page from a 1993 children’s book. An illustration shows a dump truck approaching a building site with a load of dirt. A sign says “Happy Homes Apartments - Coming Soon”. The text reads “The Mighty Dump Truck is doing an important job, too. The dirt it carries will help make the foundation for a new apartment building where families will live.”
Cat tax: a photo of a cat looking mournfully through a glass window. A red and a green LED are visible in the background, and the cat is under a chair
A screenshot of a terminal window (361 characters wide by 79 lines long) filled with gray text with no formatting. A small sample: "typeof(potential!), UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED), Nothing, Nothing, Nothing, Nothing}, Vector{Vector{Float64}}, Vector{Float64}, Vector{Vector{Vector{Float64}}}, Vector{Int64}, OrdinaryDiffEqCore.DefaultCache{OrdinaryDiffEqTsit5.Tsit5Cache{Vector{Float64}, Vector{Float64}, Vector{Float64},"
Paradise ducklings on a grassy stream bank. A mother duck is leaning forward, head pointed straight ahead, at a small bird that has landed nearby. A red circle and arrow annotates where the mother duck is about to charge.
A stream of interstellar objects spreading out over time. The video is centered on the progenitor (the object producing the interstellar objects). The x-axis is the angle around the Galaxy away from the progenitor, and the y-axis is the distance from the center of the Galaxy relative to the progenitor. Eventually the interstellar objects start wrapping around the Galaxy, forming the "braided river" pattern.
An animation of interstellar objects as they orbit in the Galaxy. The camera is looking down at the face-on Galaxy, with concentric circles marking 2 kpc (~6300 light-year) intervals away from the Galactic Center. ~100 points (stars) produce ~100 interstellar objects (represented by blue dots). Each set of points spreads out into its own long narrow stream and begin to blur together. 3 streams are colored differently (in red, purple, and maroon) so you can still see them later. The Sun's orbit is shown in orange.
A large white and gray tabby cat in a harness on a leash walking curiously towards a strip of vegetation between a large concrete surface and a wooden fence.
A screenshot of a website with a red white and blue "I Voted" sticker, labelled "County of Santa Clara". Also visible is a line in a table with the heading "Ballot Counted:" and a value of "Yes"
The Mr. Incredibles Meme. On the left is Mr. Incredible pictured smiling and in color, with the caption "Losing a factor of 2". On the right is Mr. Incredible in black and white, his face washed out by the low contrast, with the caption "Losing a factor of X^0.1"
A cat asleep on a cat tree with her front legs out of view and her back legs sticking off the platform. Red flowers and greenery are visible outside the window behind her.
Eight fluffy black and white ducklings on a small grassy hill at sunset. The mother duck, brown with a white head, follows them.
A photo of a poster, featuring an object labelled Pluto, with a parenthetical “(not part of the solar system)”
A photo of a plastic bottle containing a green liquid with a label including the words “clean, laundry liquid, apple splash.” The bottom of the bottle has the phrase in all caps “not to be taken”
A short snippet of python code creating many large scatter plots of random data and saving to a pdf file with matplotlib. The line matplotlib.use('pdf') is commented - uncommenting in avoids the memory leak by using the pdf backend instead of a default interactive backend.
A graphical summary of a new paper by Imara & Forbes. A white cylinder is overlayed on a map of the Orion B molecular cloud taken by Herschel. The big ideas in the paper are summarized as: 1) Many stellar nurseries (molecular clouds) are shaped like cylinders. (Pretty close!) 2) We introduce a model based on this assumption and apply it to real stellar nurseries in the Milky Way. 3) We find that the shape of stellar nurseries affects how efficiently they produce stars.
A photograph of highly textured low-level clouds tinted yellow at sunset, above a large field of grass. Anticrepuscular rays are visible in the center above a building in the foreground.
A tabby brown and white cat named Rocket perched next to a cardboard box of nappies, making an offer we can't refuse.
A photo of a beach with blue skies, a long white cloud off shore, and some high wispy clouds. Green plants, mostly grass, and some boulders in the foreground. A single person visible on the water. Taken at Sumner Beach in Christchurch NZ