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Alison Thomas

Astronomy projects

Choose a star to open a project, or use the Projects list below. On a touch screen, tap once for its name and again to select it. Press Escape to close a selected project. The star field is an illustration. It does not show the observations used in the projects.

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Choose from four projects

Astronomy projects

Ghostlight

A black hole can reveal itself by bending a background star’s light. This simulation tests how light from a nearby star can distort the position a telescope records.

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Calculated differences between each model and the known simulated star positions. Allowing the second star its own position leaves almost no mean difference. Forcing the stars together leaves a strong pattern over time. These curves are not telescope observations.

What the figure shows

These calculated curves come from a simulation, not telescope observations. The left panel allows the second star its own position; the right forces it onto the background star. The curves show the mean signal left unexplained. The right panel’s strong pattern shows why checking that signal should expose the incorrect model.

Source: Ghostlight’s saved deterministic residual audit.

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Echo Cartographer

Light from an accretion disk can arrive at different times at different wavelengths. Two simulation studies test how reliably those delays could be used to estimate distances around a black hole.

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Delays accepted by the response model’s selection rule in separate simulated groups: unrelated signals 0 of 128; genuine echoes with frequent observations 120 of 128; sparse observations 0 of 128; a wider response 2 of 64; slower driving variations 0 of 64.

What the figure shows

Each row shows how often the response model’s selection rule accepts a delay in a separate group of simulated campaigns. Most genuine echoes are retained with frequent observations. Sparse observations, a wider spread of response times or slower driving variations lead the rule to withhold most or all genuine delays.

Source: Echo Cartographer’s saved signal-validity results and selection-count table.

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Anatomy of a Little Red Dot

Little red dots may contain light from stars and gas around growing black holes. Three JWST spectra test what a strong brightness contrast can reveal about those light sources.

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Two panels show The Cliff. The observed JWST spectrum rises toward longer wavelengths, and a continuous bending model with added emission follows it. Four estimates of faint shorter-wavelength light use the same exposures; the fixed-box estimate’s error crosses zero, leaving its positive brightness ratio without a finite upper bound.

What the figure shows

The left panel compares The Cliff’s observed JWST spectrum with a model that changes slope but stays continuous at 3646 Å. Added emission features help the model follow the contrast. A strong difference between the shaded wavelength bands therefore does not uniquely require a sharp jump.

Data: NASA/ESA/CSA JWST; RUBIES GO-4233 (Anna de Graaff, Gabriel Brammer); DAWN JWST Archive / msaexp.

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Gaia Pleiades Member Finder

Stars that formed together often share distances and motions. Gaia measurements are used to select Pleiades candidates and examine how the selection rules change the list.

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Two scatter plots show the 866 selected Gaia stars in teal against the filtered field in gray. Their motion across the sky forms a compact group near 20 and minus 45 milliarcseconds per year. The same stars trace a curved sequence in color and brightness, a check that reuses the selected parallaxes.

What the figure shows

In the left panel, selected candidates form a compact group in motion across the sky. In the right, the same candidates trace a recognizable color-and-brightness sequence. That check reuses the selected parallaxes and does not independently confirm membership. Together the panels show the selection and a check on its stellar pattern.

Data: ESA/Gaia/DPAC, Gaia DR3. Comparison catalog: Hunt & Reffert (2024), CDS VizieR J/A+A/686/A42.

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