(ORDO NEWS) — An international team of astronomers has discovered a mysterious “ghostly” glow that surrounds the solar system, but its exact origin remains unknown.
It was found by subtracting the known interplanetary and interstellar scattered light from the extragalactic background.
The resulting value turned out to be greater than the value measured from the observations of the New Horizons station, located beyond the orbit of Pluto.
As part of the SKYSURF project, scientists analyzed 249,861 sky images taken by the Hubble Space Telescope’s (HST) Wide Field Cameras to account for all light from sources such as planets, stars, galaxies and dust.
The aim of the study was to measure the extragalactic background light (EBL) while excluding zodiacal light (ZL) and scattered galactic light (DGL) from all scattered (diffuse) cosmic light.
Zodiacal light is a faint glow in the area of the zodiac constellations, arising from the scattering of sunlight on the accumulation of dust particles lying in the plane of the solar system.
The galactic light background is caused by the light of the stars of the Milky Way scattered on interstellar clouds. Most of the extragalactic background light comes from distant galaxies and active galactic nuclei.
The EBL is the dominant background in the universe after the cosmic microwave background and is thought to be composed of short wavelength ultraviolet (0.1 micrometers) and long wavelength (1000 micrometers) far infrared radiation.
To limit the brightness of the extragalactic background light, the scientists compared the darkest HST images with theoretical models of zodiacal light, and also corrected for the DGL using a model of radiation from the Milky Way’s diffuse interstellar medium.
For images taken using the F125W, F140W and F160W infrared broadband filters, the diffuse background brightness at a wavelength of 1.25-1.6 micrometers was 29, 40 and 29 nanowatts per square meter per steradian (solid angle unit), respectively.
This is an upper bound on the brightness of extragalactic light, as the researchers were unable to accurately determine the brightness of the foreground.
It also does not take into account such a potential source of scattered light as a dim, diffuse, spherical cloud of cometary dust in the solar system.
Observing this dust in the future will help update zodiacal light models to better limit the EBL.
The existence of this dust is indicated by the fact that the New Horizons spacecraft, heading into interstellar space, recorded much weaker diffuse radiation than Hubble.
Thus, there is most likely an additional component between the Earth and where New Horizons measured, which is not taken into account by current models of zodiacal light.
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