A Decade of NuSTAR: What Its X-Ray Vision Has Taught Us

Bright green sources of high-energy X-ray light captured by NuSTAR overlaid on an optical-light image of the Whirlpool galaxy and its companion galaxy, M51b (the bright greenish-white spot above). Image: NASA

NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), led by Caltech and managed by JPL, turned 10 years old in June. This space telescope detects high-energy X-ray light and studies some of the most energetic objects and processes in the universe. The mission’s principal investigator is Fiona Harrison, the Harold A. Rosen Professor of Physics and the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy at Caltech. Here are some of the ways NuSTAR has opened our eyes over the last decade:

Seeing X-Rays Close to Home

Different colors of visible light have different wavelengths and different energies; similarly, there is a range of X-ray light, or light waves with higher energies than those human eyes can detect. NuSTAR detects X-rays at the higher end of the range. There are not many objects in our solar system that emit the X-rays NuSTAR can detect, but both the sun and Jupiter do. NuSTAR’s studies could help scientists explain why the sun’s outer region, the corona, is many times hotter than its surface. NuSTAR’s observations of Jupiter, made contemporaneously with JPL’s Juno mission, found that high energy X-rays are produced as particles slam into the planet’s atmosphere.

Fiona Harrison. Image: Caltech

Illuminating Black Holes

Black holes do not emit light, but some of the biggest ones we know of are surrounded by disks of hot gas that glow in many different wavelengths of light. NuSTAR can show scientists what is happening to the material closest to the black hole and reveal how black holes produce bright flares and jets of hot gas that stretch for thousands of light-years into space. The mission has measured temperature variations in black hole winds that influence star formation in the rest of the galaxy. Recently, NuSTAR supported the Event Horizon Telescope (EHT) in its effort to capture the first-ever direct images of the shadows of black holes.

Finding Hidden Black Holes

NuSTAR has identified dozens of black holes hidden behind thick clouds of gas and dust. Visible light typically cannot penetrate those clouds, but the high-energy X-ray light observed by NuSTAR can. In recent years, scientists have used NuSTAR data to find out how black holes become surrounded by such thick clouds, how that process influences their development, and how obscuration relates to a black hole’s impact on the surrounding galaxy.

Revealing the Power of ‘Undead’ Stars

NuSTAR is a kind of zombie hunter: It finds the undead corpses of stars. Known as neutron stars, these are dense nuggets of material left over after a massive star runs out of fuel and collapses. Though neutron stars are typically the size of a large city, they are so dense that a teaspoon of one would weigh about a billion tons on Earth. Their density, combined with their powerful magnetic fields, makes these objects extremely energetic: one neutron star located in the galaxy M82 beams with the energy of 10 million suns. Solving Supernova Mysteries Stars are mostly spherical, but NuSTAR observations have shown that when they explode as supernovae, they become an asymmetrical mess. The space telescope solved a major mystery in the study of supernovae by mapping the radioactive material left over by two stellar explosions. It traced the shape of the debris and in both cases revealed significant deviations from a spherical shape. Because of NuSTAR’s X-ray vision, astronomers now have clues about what happens in an environment that would be almost impossible to probe directly. The NuSTAR observations suggest that the inner regions of a star are extremely turbulent at the time of detonation.