- 4142 - EINSTEIN CROSS - what causes it? In 2021, the Gaia satellite found a dozen more “Einstein crosses” And, astronomers predict that more will be found as more powerful instruments and techniques perform surveys like Gaia’s. More lenses like these will extend astronomy’s view to earlier epochs. They could perform as excellent probes of the dark matter distribution in the different epochs of cosmic time.
-------------- 4142 - EINSTEIN CROSS - what causes it?
- Gravitational lensing is one of astronomy’s
great wonders. It is a natural lens that
magnifies the distant universe. Sometimes a lensing system takes the shape of a
so-called “Einstein Cross”. Those are rare and amazingly useful ways to study
objects far away in space and time.
-
- Astronomers recently found a new Einstein
cross using the “Dark Energy Spectroscopic Instrument” mounted on a telescope
at Kitt Peak National Observatory. This instrument is surveying the sky and has
found many instances of gravitational lensing proving to be both beautiful and
a scientific treasure trove of information about the early universe.
-
- The lens system, DESI-253.2534+26.8843, is
actually a massive foreground elliptical galaxy surrounded by four blue images
of a background galaxy. The four images
that display consistent spectral features tell the astronomers that the source
is a single galaxy, which allowed them to confirm the lens system.
-
- The cross pattern tells astronomers about
the mass distribution of the lens galaxy. Elongated mass distributions result
in Einstein crosses, and a spherical mass distribution would result in an
Einstein ring.
-
- This latest Einstein Cross has some
interesting statistics. The main galaxy doing the lensing lies about 5.998
billion light-years away. The distant galaxy that it’s lensing is more than
11.179 billion light-years away. This foreground lensing galaxy is giving an
amazing look at a galaxy in the early Universe.
-
- The astronomy team determined the distance
to the more distant galaxy by doing a spectral analysis of the light in each
image. Based on color information contained in the 'DESI Legacy Survey”, the
team thinks that the lensing galaxy is in a galaxy group. They found at least
seven other members of the same group. They describe those galaxies as
“passive”, which could mean they are all older or elliptical.
-
- Using data from the “Multi-Unit
Spectroscopic Explorer” (MUSE) at the Very Large Telescope in Chile, it turned
out the background object is very typical of a starburst galaxy. They also
found traces of a faint galaxy lying in front of one of the lensed images. It’s
about 4.2 billion light-years away.
-
- This study benefits from advances in
computer modeling and hardware. It is
part of a bigger project to confirm and parametrize many gravitational lens
candidates discovered in the DESI legacy survey data using neural networks.
-
- MUSE is a powerful spectroscopic instrument
that can cover wide areas of the sky in visible light wavelengths. It dissects
the light into its component wavelengths (creating spectra) and each pixel in
the image from the integral field unit contains a spectrum.
-
- What Makes an Einstein Cross? When a massive galaxy sits directly “in
front of” a more distant background object (such as a galaxy or a quasar) the
distribution of matter around that galaxy and its gravitational effect can
“bend” the light from the object as it passes by. That results in lensed images
or a ring.
-
- The first “Einstein Cross” was a surprise
discovered it in 1985. It’s called “Huchra’s Lens”. It really looked baffling
to the observers, as if there were four identical quasars around the center
where there was a faint image of the quasar.
-
- To figure out exactly why this would
happen, the astronomers studied the light from each “image”. Eventually, the
redshift of the light from the quasar revealed that it lay 8 billion
light-years away. The lensing galaxy is only about 400 million light-years
distant.
-
- It turns out that gravitational lensing
happens everywhere in the universe, mostly in the form of so-called “weak
lensing”. Creating an Einstein Cross requires a precise alignment of the
lensing body and light source and astronomers refer to this as “strong
gravitational lensing”.
-
- One of the goals is to do a targeted search
for supernovae in hundreds of gravitational lens systems, which will allow us
to directly measure Hubble’s constant by observing the time delay of supernova
light curves between the lensed images of a supernova.
-
-
September 5, 2023 EINSTEIN
CROSS - what causes it? 4142
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