Variability class

Other variables

Not every variable star in VSX is a star, and not every variable is cleanly typed. This class holds what fits nowhere else: active galactic nuclei, X-ray binaries, rare pulsators, and the genuinely unclassified.

858,715 starsVAR · AGN · LMXB

active galactic nucleus · schematic

Timet 0 d

what is shining

Schematic: aperiodic red-noise variability. No period to fold.

What it is

Everything that fits none of the other seven classes: active galactic nuclei and quasars (accreting supermassive black holes in distant galaxies), high- and low-mass X-ray binaries, unusual or under-studied pulsators, and stars marked simply variable or unclassified in VSX.

Untyped variables

Most stars here have no specific VSX type (VAR, MISC and similar); the classifier's prediction on each star page is the best available guess. AGN have no stellar distance and no single period, so diagrams that need either leave them out.

VSX types

Subtypes

Active galactic nucleus

AGN

Accreting supermassive black hole; stochastic, aperiodic optical flicker. Extragalactic.

Quasar

QSO

The luminous, distant end of the AGN family — variable on timescales of days to years.

Low-mass X-ray binary

LMXB

A compact object accreting from a stellar companion; optical variability tracks the accretion flow.

Untyped variable

VAR

Confirmed variable, classification undetermined — a candidate for the classifier, not a verdict.

Method

Finding the period

Mostly aperiodic, so period-finding is the wrong question. AGN variability is red noise — a damped random walk that produces seductive but spurious GLS peaks. varchive treats this class as the place where variability indices and the classifier's anomaly and out-of-distribution scores do the work, not the periodogram. A real period does sometimes turn up (an X-ray binary's orbit, say).

Pitfalls

Red-noise wander mimics periodicity — a tall GLS peak on an AGN is almost always an artifact.
This is a heterogeneous bag by construction, so aggregate statistics over the whole class are close to meaningless.
It is a residual, not a physical family — a star landing here often just means VSX hasn't typed it yet.
Extragalactic objects have no meaningful stellar distance, so color-magnitude and period-luminosity diagrams legitimately leave them out.

Archive stars