اپست ِ هممیاو
Fr.: distance comobile
1) A distance in → comoving coordinates
between two points in space at a given cosmological time. In other words,
the distance between two nearby objects in the Universe which
remains constant with epoch if the two objects are moving with the
→ Hubble flow.
More specifically, it is the → proper distance
divided by the ratio of the → scale factor
of the Universe between then, a(t)em,
and now, a(t)obs:
DC = Dproper .
In terms of → redshift (z),
it is the proper distance multiplied by (1 + z).
At the present epoch, i.e. a = a(tobs) = 1,
DC = Dproper.
If the objects have no peculiar velocity their comoving distance at
any time is the same as their distance today.
The comoving distance of the → cosmic horizon
is about 48 × 109→ light-years.
2) Transverse comoving distance: In a non-flat Universe,
the comoving distance
between two events at the same → redshift but separated on
the sky by some angle. It is expressed by trigonometric functions of
→ curvature, → comoving distance,
and the → Hubble distance accounting for
the curvature of space.
In a flat universe (Ωk)
it is the same as the → comoving distance.
3) Line-of-sight comoving distance:
The total line-of-sight comoving distance from us to a distant
object computed by integrating the infinitesimal comoving distance
contributions between nearby events along the radial ray from
the time temit, when the light from the object was emitted,
to the time tobs, when the object is observed.
→ comoving; → distance.