XMM-Newton AO-26 Call for Proposals Is Open Until 9 October 2026: Your Rare Invitation to the X-Ray Cosmos

Paris, France, Source :. Astronomers, this one is for you. The European Space Agency, with significant NASA participation, has opened AO-26, the 26th call for XMM-Newton observing proposals. Submissions close on Friday, 9 October 2026 at 12:00 UTC, and the official announcement went out on 19 August 2026. That gives you a solid window to design a program that could answer some of the biggest questions in high-energy astrophysics.

What makes this worth your time? XMM-Newton has been delivering on that promise since December 1999. The X-ray Multi-Mirror Mission, named after Isaac Newton, uses three large telescopes with nested, gold-coated mirrors. Those mirrors are designed to capture X-rays from the most extreme environments in the cosmos. Think of black holes pulling in gas, neutron stars with magnetic fields so strong they reshape matter nearby, supernova remnants moving at thousands of kilometers per second, and galaxy clusters filled with superheated gas. The X-rays from these objects carry information about temperature, density, and motion. XMM-Newton reads that information and gives scientists a way to understand what is happening in places beyond the reach of ordinary telescopes.

Earth's atmosphere absorbs X-rays, so this kind of exploration is reserved for orbit. That makes every XMM-Newton observation a look at processes in the high-energy sky that are otherwise hidden from ground-based instruments. More than that, it makes the observatory a perfect platform for discovering what is changing, what is brightening, and what is moving in that sky.

There is also an unusually broad set of partnerships in this cycle. The XMM-Newton Project has arranged joint observation programs with the Very Large Telescope, NRAO's VLA, GBT, and VLBA, the Hubble Space Telescope, JWST, and the ground-based gamma-ray telescopes HESS and MAGIC. On the X-ray side, proposals can coordinate with Chandra, NuSTAR, Swift, XRISM, and, new for this cycle, IXPE. In practical terms, an approved XMM-Newton program can become part of a true multiwavelength campaign. The same source could appear in radio, optical, infrared, ultraviolet, gamma rays, and multiple X-ray bands, all from one proposal. Some approved programs may even receive observing time on partner facilities through XMM-Newton's own allocation. That is a major advantage if your science depends on correlating activity across the entire spectrum.

The route to those observations is straightforward. You propose specific targets and explain what the data would reveal about extreme gravity, matter under intense conditions, or the formation and evolution of large-scale cosmic structures. A peer review panel then ranks proposals based on scientific priority and technical feasibility. XMM-Newton's high collecting area and long, uninterrupted visibility make it especially well suited to faint-source spectroscopy, timing studies of compact objects, and deep surveys that aim at distant, low-luminosity sources. If your idea needs one of these strengths, the telescope is designed for it.

The formal invitation from ESA's Director of Science has already been distributed, and full details about instrument status, target visibility, and partner observatory procedures are in the official announcement. All proposals must be submitted electronically before the deadline. The cutoff is Friday, 9 October 2026 at 12 noon UTC, or 8 a.m. Eastern Time and 5 a.m. Pacific Time in the United States. With IXPE newly included and coordination opportunities spanning nearly every major telescope in operation, AO-26 could be one of the most competitive and consequential X-ray observing seasons in recent memory. If you have a question that only the X-ray universe can answer, this is your chance to ask it.