Denis Erkal

@derkal.bsky.social

529 Followers 255 Following

Astrophysicist working on dark matter, near-field cosmology, and galaxy formation. All opinions are my own. He/him.

Picture of the Cygnus loop showing lots of stars and thin clouds of gas which came from a supernova explosion
Screen shot of Google search for (3e19m)/(1 kpc) which gives an answer of 55.7 instead of the correct answer of 0.97
Screen shot of a Google search showing (3e19 m)/(1 kpc) gives 55.7
Seestar image of Palomar 5 showing a few bright stars and many faint stars
Image of two galaxies. The whale galaxy on the top is a long edge-on disk. The bottom galaxy, the hockey stick galaxy, shows a sharp hook due to an interaction with another galaxy in the group.
Photo of the eclipse during showing a part of the sun obscured by the moon. Looks a bit like a Pac-Man
Plot showing how the stream of Sagittarius would look in cold dark matter versus self-interacting dark matter. The left panel shows cold dark matter and has a large spur coming off the stream. The right panel shows self-interacting dark matter with a much smaller spur.
Plot showing the dark matter in cold dark matter versus self-interacting dark matter. Left panel shows a stream of dark matter with a dark matter clump at the progenitor's location. Right panel shows a broader stream in self-interacting dark matter. There is no dark matter clump at the progenitor's location since it is fully evaporated due to self-interacting dark matter.
Image of the Orion Nebula showing a bright cloud in the center and stars in the outskirts.
Image of the M3 globular cluster which shows a dense clump of stars in the middle of the field and a lower density of stars from the Milky Way farther away
Image of the whirlpool galaxy
Movie showing how NGC 1904 disrupts in the Milky Way. The left panel show a view centered on the Milky Way and the right panel shows a view centered on the globular cluster. The stars are stripped from the globular cluster at each pericenter. These stars move ahead and behind the globular cluster. The most recent stripping episode produces a linear feature near the globular cluster which is what produces the dumbbell on the sky.
Graph showing the N-body simulation of NGC 1904 compared with observations. The left panel shows the N-body simulation on the sky colored by distance. There is a clear gradient across in the dumbbell of stripped stars. The 2nd panel shows the selection of these dumbbell stars in the data. The 3rd panel shows the CMD of these stars with the stars on the top of the dumbbell fainter than those on the bottom. The final panel shows the CMD if we correct for the distance gradient which shows the stream stars sitting on a narrow isochrone.
Movie showing NGC 1904. The left panel shows the observed members which show a dumbbell-like overdensity near NGC 1904. The right panel shows an N-body simulation on the same orbit which has the same dumbbell morphology. The right panel also rotates around, showing the 3d structure of the dumbbell with part of the structure pointed towards us as part of it pointed away from us.
Plot of speed versus time for men’s and women’s swimming and running events. The y-axis shows the speed and the x-axis shows time. All speeds are normalized to the speed of the shortest event and only drop to ~60% max speed after 2 hours.
Aurora with pink and green bands
Plot of on sky l versus b for the subahlo’s present-day position showing it is well localized
Subhalo mass versus scale radius showing we can recover it well
Triangle plot showing posterior parameters of the subhalo properties, all of which we well fit.
Picture of Denis giving a talk with a slide titled “How to weigh the Milky Way”
A DALL-E drawn scene where the left side is day time and the right side is nighttime. The view is a landscape flanked by mountains with a river going off into the distance. The day sky has a sun, clouds, and streaks of sunlight. The night sky has stars, the moon, the Milky Way, and a aurora.
A picture of a stream of of stars with an S-shaped bend in the middle. A globular cluster sits at the middle of the S and a space ship flies past the stream.
A horse running on a treadmill which is powering a wooden cart with wheels
Experimental setup showing rubber bands attached to one side of a seesaw made of Meccano. The rubber bands go from the seesaw to a base plate the seesaw is sitting on. The other side of the seesaw has a laser pointer on it.
Person with a bike pump and a white balloon covered in black dots giving a presentation
Plot of inflation corrected salary showing that the buying power of a UK academic salary has gone down significantly over 14 years.
Image of the Whirlpool galaxy showing its low surface brightness outskirts which resulted from a tidal interaction.
Image of the Whirlpool galaxy showing faint tidal debris its outskirts.
A snail with a dotted slime trail