Even on a sunny day, the human eye cannot see all the light emitted by our nearest star. A new image shows some of this hidden light, which includes high-energy X-rays emitted by the hottest material in the Sun’s atmosphere, as observed by the Nuclear Spectroscopic Telescope Array (NuSTAR) at The NASA. Although this observatory typically 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), NuSTAR data is represented in blue and overlaid with observations from the X-ray Telescope (XRT) aboard the Japan Aerospace Exploration Agency (JAXA) Hinode mission. in English), represented in green, and from the atmospheric imager (AIA) aboard NASA’s Solar Dynamics Observatory, represented in red. NuSTAR’s relatively small field of view means that it cannot see the entire Sun from its position in Earth’s orbit, so this 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. By contrast, Hinode’s XRT detects low-energy X-rays and the Solar Dynamics Observatory’s AIA detects ultraviolet light, wavelengths waves emitted from the entire face of the Sun.
The Sun looks different depending on who is looking at it. From left to right: NASA’s NuSTAR observatory 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.
Credits: NASA/JPL-Caltech/JAXA
NuSTAR’s view could help scientists solve one of the biggest mysteries about our closest star: why the Sun’s outer atmosphere, called the corona, reaches over a million degrees; it is at least 100 times hotter than its surface. This has puzzled scientists because the Sun’s heat originates in its core and travels outward. It’s as if the air around a fire is 100 times hotter than the flames.
The source of the corona’s heat may be small eruptions in the Sun’s atmosphere called nanoflares. Flares are large eruptions of heat, light, and particles that are visible to a wide variety of solar observatories. Nanoflares are much smaller events, but both types of events produce material even hotter than the average temperature of the corona. Regular flares do not occur frequently enough to keep the corona at the high temperatures scientists are seeing, but nanoflares could occur much more frequently, perhaps enough to collectively heat the corona.
Although individual nanoflares are too faint to be seen in the hot light of the Sun, NuSTAR is able to detect light from the high-temperature material thought to be produced when a large number of nanoflares occur, one near the other. This ability allows physicists to investigate how often nanoflares occur and how they release energy.
The observations used in these images coincided with the twelfth close approach to the Sun, or perihelion, by NASA’s Parker Solar Probe, which is traveling closer to our star than any spacecraft in history. Observing with NuSTAR during one of the Parker Probe’s perihelion passes allows scientists to link remotely observed activity in the Sun’s atmosphere with direct samples of the solar environment obtained by the probe.
More about the mission
NuSTAR was launched on June 13, 2012. This is a Small Explorer mission led by Caltech in Pasadena, California, and managed by the Jet Propulsion Laboratory (JPL) for the Science Mission Directorate of the NASA in Washington, and was developed in partnership with the Danish Technical University (DTU) and the Italian Space Agency (ASI). The telescope’s optics were built 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. NuSTAR’s mission operations center is located at the University of California at Berkeley and the official data archive is located at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission ground station and a mirror data file. Caltech manages JPL for NASA.
For more information about NuSTAR, visit the website: www.nustar.caltech.edu
By Calla Cofield
Jet Propulsion Laboratory, Pasadena, California
Read this story in English here.