Stellsignalen

Stellsignalen, or stellar signals, is a broad term used to describe observable signals that originate from stars or their environments and carry information about their physical state, activity, or around-star companions. The term is common in Dutch-language astronomy and is also used in discussions related to the search for extraterrestrial intelligence to cover a range of phenomena that vary in time and wavelength.

Stellar signals can take many forms. Photometric signals include periodic dimming or brightening caused by transiting planets, intrinsic stellar pulsations, star spots, and flares. Spectroscopic signals involve radial-velocity variations produced by orbiting bodies or by changes in the star’s atmosphere due to activity cycles. Asteroseismic signals arise from oscillations inside stars, detectable in light or velocity, and can reveal internal structure. Astrometric signals are tiny positional shifts on the sky caused by companions, while radio signals may originate from magnetic activity or interactions in stellar environments.

Detection and analysis rely on time-domain astronomy and a range of instruments. Photometric signals are captured by space telescopes such as Kepler and TESS; spectroscopic signals by high-precision spectrographs such as HARPS or ESPRESSO; astrometric signals by Gaia; and possible radio signals by arrays like the VLA or future facilities. Data analysis employs Fourier transforms, periodograms, transit models, and statistical validation to distinguish genuine signals from noise or instrumental effects.

Significance lies in determining stellar parameters, probing internal structure through asteroseismology, and characterizing exoplanets and their systems. A central challenge is separating true stellar signals from artifacts, noise, and stellar activity. In SETI discussions, stellsignalen can refer to the hypothetical presence of intentional communications, but in mainstream astronomy most observed signals are interpreted as natural phenomena pending robust verification.