An Early End for the Chandra X-Ray Observatory?

After a quarter century in space, NASA’s Chandra X-ray Observatory might be coming to an end, at least according to a new budget for NASA . . . but that won't happen if astronomers have anything to say about it.

NASA's budget for 2025 and projections forward foresee a steep reduction in funding for Chandra. This change would also slash support for research projects in X-ray astronomy, especially in the U.S. — which in turn affects both professional astronomers and students who rely on that funding to do their work. Astronomers are now lobbying to save the telescope.

The Numbers

President Biden’s FY2025 budget calls for NASA to decrease funding for the X-ray telescope by unprecedented amounts. For context, Chandra received $68.3 million for normal operations in 2023. Now, under the FY25 budget and projections for following years, funding for the telescope would drop to $41.1 million in FY25 (which starts this October) and $26.6 million in FY26. By 2029, funding would taper to just $5 million, after which the mission would shutter for good.

Patrick Slane (Center for Astrophysics, Harvard & Smithsonian), director of the Chandra X-ray Center, notes that the levels of funding being proposed are not enough for the telescope to continue making observations. In a letter to the Chandra community, he states, "The funding levels provided in the new budget plan are consistent with levels for . . . closeout activities, but lower than can accommodate operation of the Chandra science mission."

NASA cites Chandra’s downgraded performance over time as a reason to draw the mission to an end. For example, the efficiency at which the main detector picks up X-rays has decreased over the years due to the build-up of contamination. Likewise, an increase in temperature creates restrictions in scheduling observations.

However, Slane has also taken issue with that claim, noting that workarounds have been found to obtain good science out of Chandra’s instruments, with no decease in observing efficiency or quality of science.

Astronomers in the community have likewise reacted to the news, starting a grass-roots organization, SaveChandra, to promote awareness for the mission and the role it serves for X-ray astronomy.

Chandra's X-ray Vision

Deployed from the payload bay of Space Shuttle Columbia on July 23, 1999, Chandra was one of NASA's four Great Observatories, which also included the Spitzer Space Telescope (an infrared mission), the Compton Gamma Ray Observatory, and the still-operational Hubble Space Telescope. (The budget for Hubble is likewise being cut, though less drastically, by 5%.)

Named after the astrophysicist Subrahmanyan Chandrasekhar, Chandra has remained in service for 25 years. When it launched, it had an unprecedentedly sharp-eyed view of X-rays, using ultrasmooth mirrors to guide the high-energy radiation to a focus.

Chandra's unparalleled resolution has enabled astronomers to see the neutron star pulsing at the center of the Crab Nebula, peer into the hot gas around the supermassive black hole in the core of our galaxy, and uncover shock waves emanating from Supernova 1987A.

Even now, its views are unsurpassed. While several other X-ray missions have launched since then, each with their own strengths — including NASA's NuStar, the joint JAXA/NASA XRISM mission and ESA’s XMM-Newton — none can match the sharpness of Chandra's X-ray vision.

“Chandra has by far the highest spatial resolution (the level of detail that we can see in the images) than any other X-ray facility," says Tea Tenim (Princeton University), adding that Chandra's images are 10 times sharper than XMM-Newton's, 30 times sharper than NuSTAR, and 150 times sharper than XRISM. As such, the mission is the only one that can come close to synergy with the high-resolution views of the James Webb and Hubble telescopes.

Looking forward, the next X-ray mission in the pipeline for NASA is Lynx; however, it wouldn’t launch before the 2040s at the earliest. ESA’s Athena isn’t set to launch before the late 2030s. Smaller X-ray mission concepts, such as the Line Emission Mapper (LEM) and the Advanced X-ray Imaging Satellite (AXIS), are also still at early stages.

The astronomers of SaveChandra argue that perhaps the biggest risk, if Chandra closes down untimely soon, is that the workforce and expertise for those future missions will simply not be there.