Even on a sunny day, the human eye cannot see all the light emitted by the nearest star. The new image shows some of this hidden light, including high-energy X-rays emitted by the hottest material in the Sun’s atmosphere, as observed by NASA’s Nuclear Spectroscopic Telescope ( NuSTAR ). While the observatory usually studies objects outside our solar system, such as massive black holes and collapsed stars, it has also provided astronomers with information about our Sun .
In the composite image above (left), the NuSTAR data are shown in blue and are superimposed on the X-ray Telescope (XRT) observations during Hinode missions The Japan Aerospace Exploration Agency, represented in green, and the Atmospheric Imagery Assembly (AIA). at NASA’s Solar Dynamics Observatory ( S.D.O ), represented in red. NuSTAR’s relatively small field of view means it can’t see the entire Sun from its position in Earth orbit, so the observatory’s view of the Sun is actually a mosaic of 25 images taken in June 2022.
The high-energy X-rays observed by NuSTAR appear in only a few places in the Sun’s atmosphere. In contrast, Hinode’s XRT detects low-energy X-rays, while SDO’s AIA detects ultraviolet light — the wavelengths that are emitted throughout the Sun’s surface.
The sun looks different depending on who is looking. At left, NASA’s NuSTAR sees high-energy X-rays; The Japan Aerospace Exploration Agency’s Hinode mission sees lower-energy X-rays; and NASA’s Solar Dynamics Observatory sees ultraviolet light. Credit: NASA/JPL-Caltech/JAXA
NuSTAR’s view can help scientists solve one of the of the greatest secrets of the star closest to us : why the temperature of the Sun’s outer atmosphere, called the corona, reaches more than a million degrees – at least 100 times hotter than its surface. This has puzzled scientists because the Sun’s heat originates in its core and spreads outward. It is as if the air around the fire were 100 times hotter than the flame.
The source of the corona’s heat can be small eruptions in the Sun’s atmosphere, called nanoflares. Flares are large bursts of heat, light and particles visible to many solar observatories. Nanoflares are much smaller events, but both types produce material even hotter than the average coronal temperature. Regular flares don’t happen often enough to keep the corona at the high temperatures scientists observe, but nanoflares can happen much more often — perhaps often enough to heat the corona together.
Although individual nanoflares are too faint to be seen in the blazing light of the Sun, NuSTAR can detect light from high-temperature material thought to form when large numbers of nanoflares occur in close proximity to each other. This ability allows physicists to study how often nanoflares occur and how they release energy.
The observations used in these images coincided with the 12th close approach to the Sun, or perihelion, by NASA’s Solar Probe Parker Solar Probe , which flies closer to our star than any other spacecraft in history. NuSTAR observations during one of Parker’s perihelion passes allow scientists to link remote activity in the Sun’s atmosphere with direct samples of the solar environment taken by the probe.
More about the mission
NuSTAR was launched on June 13, 2012. The Small Explorer mission, led by Caltech in Pasadena, California and managed by JPL for NASA’s Science Mission Directorate in Washington, was developed in partnership with the Technical University of Denmark (DTU) and the Italian Space Agency. (ASI). The telescope’s optics were created by Columbia University, NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and DTU. The spacecraft was built by Orbital Sciences Corp. in Dulles, Virginia. The NuSTAR mission operations center is at the University of California, Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Research Center.