The brightest object of the solar system in X-rays is the Sun, but other bodies shine as well:
The Moon: reflected solar X-rays/fluorescence from solar wind and cosmic rays (700W=7×109 erg/s)
Chandra’s observations of the Moon solved a decade-long mystery about X-rays detected by ROSAT that were thought to be coming from the dark portion of the Moon. It turns out that these X-rays only appear to come from the Moon and can be explained by radiation from Earth’s geocorona.
Other X-ray emitting bodies in the solar system:
Planets: Jupiter (LX~1015 erg/s), Mars, Venus: fluorescence X-rays from upper atmosphere (≥100 km)
Comets: LX~1016 erg/s
A short review of the main X-ray emitters in the solar system can be found in: X-ray Studies of Planetary Systems: An Astro2010 Decadal Survey White Paper and SOFT X-RAY EMISSIONS FROM PLANETS, MOONS, AND COMETS (see attached material).
The brightest X-ray source in the Solar system is the SUN.
N.B. Plasma prevents convection and conduction.
The turbulence in the upper layer of the star creates magnetic loops trapped inside the sun’s plasma, whose energy can heat the corona to temperatures that allow it to emit X-rays.
This is a solar coronal loop imaged by the TRACE satellite.
The Sun has a surface temperature of only 5800 K – nowhere near the 106 K needed to generate X-rays.
Solar X-ray activity comes from the Sun’s corona, seen here in a composite image (red = lower corona from Yohkoh; blue/white = extended corona from HAO electron-scattering coronagraph).
The solar corona at different stages of the solar cycle, as seen from the SOHO satellite. Courtesy of NASA.
Features of the solar corona as seen in a magnetogram and in the extreme ultraviolet. Courtesy of NASA.
The basic model explaining the X-ray emission from the stellar corona, as well as its variability and close connection with the solar cycle, is the so called “dynamo model”.
In this model differential rotation (faster at the equator) in the sun, combined with internal shear at the interface between radiative and convective layers, generate magnetic field lines and cause them to become wrapped and tangled around its surface.
The rotational energy of the Sun (as in all low-mass stars, see next lecture) is trapped in its magnetic field and released in the form of UV and X-ray emission.
13. X-ray binaries
Haisch & Schmitt, 1996. “Advances in Solar-stellar astrophysics.”
Pallavicini et al. 1981. “Relations among stellar X-ray emission observed from Einstein, stellar rotation and bolometric luminosity.”