Astronomers have identified 104 magnified stellar events in a single distant galaxy, more than doubling the previous count of 44 in the same object.
The galaxy, known as the Dragon, lies about 6.5 billion light-years away, at a redshift of 0.725. Its light reaches the James Webb Space Telescope smeared into a long arc.
That arc is the work of gravity. The galaxy cluster Abell 370 sits between the Dragon and Earth, and its mass bends and concentrates the light passing through it.
Individual stars in a galaxy that distant are far too faint for any telescope to resolve. When one happens to pass behind a dense knot of mass inside the cluster, the magnification spikes and the star becomes briefly detectable.
The team compared Webb images collected between 2022 and 2024 to find the events that appeared and vanished between observations. The paper reports that "we obtain a catalog of 104 unique CCEs in the Dragon arc".
The search used the NIRCam instrument across the F150W, F200W and F410M filters, covering wavelengths from 1.3 to 4.3 microns. The paper carries the digital object identifier 10.1051/0004-6361/202660640.
The study was led by Jose Maria Palencia of the Institute of Physics of Cantabria and published in Astronomy & Astrophysics on 30 September.
The catalogue is now large enough to support statistics about the stars themselves. The ratio of blue to red supergiants came out at roughly one, which the authors say "suggests that both BSGs and RSGs contribute to the observed CCEs".
How the events are distributed also bears on what the cluster's dark matter is made of. The paper notes that one feature of the data "could provide a hint of a fuzzy nature of DM".
It is worth being clear about which instrument did the work here. Webb has a 6.5-metre mirror. The magnification that made these stars visible at all was supplied by a galaxy cluster.
This newspaper considers the credit badly distributed. Abell 370 is the larger optical component by a margin that does not require calculating.
Our analysts note that the cluster achieved this without a proposal, a principal investigator or an allocation of observing time. It was not peer-reviewed. It has never been asked to justify its programme to a committee.
The arrangement also runs without any scheduling at all. The cluster magnifies whatever happens to be behind it, continuously, in every direction, and sends the results to everybody.
The Department of Unnecessary Research has submitted the only sensible request for the next observing cycle. It asks that Abell 370 be listed as the facility, and Webb as the eyepiece it is aimed through.