QSO 0957+561 - "Twin Quasar"
Credit: ESA/Hubble & NASA
In this new Hubble image two objects are clearly visible, shining
brightly. When they were first discovered in 1979, they were thought to
be separate objects — however, astronomers soon realised that these
twins are a little too identical! They are close together, lie at the
same distance from us, and have surprisingly similar properties. The
reason they are so similar is not some bizarre coincidence; they are in
fact the same object.
These cosmic doppelgangers make up a double quasar known as QSO
0957+561, also known as the "Twin Quasar", which lies just under 14
billion light-years from Earth. Quasars are the intensely powerful centres of distant galaxies. So, why are we seeing this quasar twice?
Some 4 billion light-years from Earth — and directly in our line of
sight — is the huge galaxy YGKOW G1. This galaxy was the first ever
observed gravitational lens, an object with a mass so great that it can
bend the light from objects lying behind it. This phenomenon not only
allows us to see objects that would otherwise be too remote, in cases
like this it also allows us to see them twice over.
Along with the cluster of galaxies
in which it resides, YGKOW G1 exerts an enormous gravitational force.
This doesn't just affect the galaxy's shape, the stars that it forms,
and the objects around it — it affects the very space it sits in,
warping and bending the environment and producing bizarre effects, such
as this quasar double image.
This observation of gravitational lensing, the first of its kind,
meant more than just the discovery of an impressive optical illusion
allowing telescopes like Hubble to effectively see behind an intervening
galaxy. It was evidence for Einstein's theory of general relativity.
This theory had identified gravitational lensing as one of its only
observable effects, but until this observation no such lensing had been
observed since the idea was first mooted in 1936.
Links:
- ESA/Hubble release: Gravitational telescope creates space invader mirage
- ESA/Hubble release: Lenses galore — Hubble finds large sample of very distant galaxies
- ESA/Hubble release: Hubble finds double Einstein ring
Source: ESA/Hubble - Space Telescope
