Hubble's Double Take
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 realized 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 centers 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.
The first detection of gravitational lensing 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 the observation of these quasar
"twins," no such lensing had been observed since the idea was first mooted in
1936.
Image Credit: NASA/ESA
NASA
Guillermo Gonzalo Sánchez Achutegui
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