In 1892 Sherburne Wesley Burnham reported that σ Ori A was itself a very close double, although a number of later observers failed to confirm it.

[22] σ Ori A was discovered to have a variable radial velocity in 1904, considered to indicate a single-lined spectroscopic binary.

[30] A large number of brown dwarfs were found in the same area and at the same distance as the bright σ Orionis stars.

[32] The σ Orionis cluster is part of the Ori OB1b stellar association, commonly referred to as Orion's Belt.

It has been calculated that star formation in the cluster began 3 million years (myr) ago and it is approximately 360 pc away.

[6] In the central arc-minute of the cluster five particularly bright stars are visible, labelled A to E in order of distance from the brightest component σ Ori A.

[33] An infrared and radio source, IRS1, 3.3" from σ Ori A that was considered to be a patch of nebulosity has been resolved into two subsolar stars.

[40] The cluster also contains a pair consisting out of the brown dwarf SE 70 and the planetary-mass object S Ori 68, which are separated by 1700 astronomical units.

[41] In 2024 high-resolution imaging with ALMA of K-stars and early M-stars showed gaps and rings in the disks around these stars.

The disks in the cluster are small, either due to external photoevaporation by σ Orionis or the intermediate age of the region.

Lines representing a B0.5 main sequence star have been shown to belong to its close companion Ab, which has a temperature of 31,000 K and a luminosity of 18,600 L☉.

Although they cannot be directly imaged with conventional single mirror telescopes, their respective visual magnitudes have been calculated at 4.61 and 5.20.

Its visual magnitude of 5.31 is similar to σ Ori Ab and so it should be easily visible, but it is speculated that its spectral lines are highly broadened and invisible against the backdrop of the other two stars.

Within their large margins of error, these can all be considered to be consistent with each other, although it is harder to reconcile them with the 2-3 Myr estimated age of the σ Orionis cluster as a whole.

Its size, temperature, and brightness are very similar to σ Ori E but it shows none of the unusual spectral features or variability of that star.

[2] The magnetic field is highly variable from −2,300 to +3,100 gauss, matching the brightness variations and the likely rotational period.

This requires a magnetic dipole of at least 10,000 G. Around minimum brightness, a shell type spectrum appears, attributed to plasma clouds rotating above the photosphere.

[26] It was at one point suggested that σ Ori E could be further away and older than the other members of the cluster, from modelling its evolutionary age and size.

[16] However, Gaia parallaxes place σ Ori E within the cluster, and later modelling has suggested that it is very young, at less than a million years old.

The fainter object is very unusual, showing a diluted M7 or M8 absorption spectrum with emission lines of hydrogen and helium.

The observed infrared emission, peaking at around 45 microns, can be modelled by two approximately black-body components, one at 68K and one at 197 K. These are thought to be produced by two different sizes of dust grains.

The dust becomes decoupled from the gas that carried it away from the molecular cloud by radiation pressure from the hot stars at the centre of the σ Orionis cluster.

Low luminosity late class O stars should commonly produce bow waves if this model is correct.