ASASSN-21qj

Two worlds collided, 1800 light years away. Title: "A planetary collision afterglow and transit of the resultant debris cloud", by Matthew Kenworthy at Leiden, crediting also a number of astronomers both professional and amateur. I don't have Nature access so I'm piecing stuff together here.

As an amateur myself - at blogging - first, a review of the media. Science Daily transmitted a press-release from Bristol. Whoever's running their social-media needs to be hauled into the main office and told to do better, starting with relaying the title of the research which they didn't do. Science Daily meanwhile should quit relaying such releases if the releases don't release the bare minimum.

The Grauniad probably has the best recap although I dislike their term "citizen scientist". Also you have to look up the astronomers themselves to tell us, explicitly, that US-citizen Arttu Sainio was the scientist in question.

As a heat event, this was spotted by Neowise's infrared. WISE is a wide-ranging observer so only catches this one every 300 days or so, per the astronomers. JWST should be able to see more.

December 2021 is when the star tagged "ASASSN-21qj" suddenly dimmed. This occasioned the amateur social-media data-hunt; Sainio noted a brightening 900 days prior which WISE did not catch. That flash was 1000 K (maintained to this day per Grauniad) and 4% as luminous as its very star. Said star, it happens, is young: 300 My. That flash, then, is considered a crash. I don't think the team could get angular-separation directly, from this low-parallax, but the period is about 2.5 years so they just Keplered it based on a one-solar-mass barycentre - several to tens of Earth masses at 2-16 AU. Namechecked as other possible collisions: NGC 2354–ID8, HD 166191, and V488 Persei.

At that separation from a star, these were proto-icegiants, in the sooty sector. Their 1000 K mixer is now a spinning object potentially hundreds of times the size of Earth per Grauniad. I believe that "potentially" refers to the Hill Sphere.

BACKDATE 10/12