- 4110 - EINSTEIN CROSS - a new model for the Universe? Astronomers have discovered a stunning, rare example of an "Einstein cross" splitting and magnifying light from the far depths of the universe. One foreground elliptical galaxy, around 6 billion light-years from Earth, has warped and quadrisected a bright beam of light from a background galaxy about 11 billion light-years from our planet.
-------------- 4110 - EINSTEIN CROSS - a new model for the Universe?
- The resulting pattern, first predicted by
Albert Einstein in 1915, shows four smudges of blue light haloed around the
orange of the foreground galaxy, a rare arrangement that astronomers will study
to get a better understanding of the universe.
-
- The background light likely comes from a
quasar, a young galaxy whose supermassive black hole at its core gobbles up
enormous amounts of matter and blasts out enough radiation to shine more than a
trillion times more brightly than the brightest stars.
-
- Einstein's theory of general relativity
describes the way massive objects warp the fabric of the universe, called
space-time. Gravity, Einstein discovered, isn't produced by an unseen force;
rather, it's simply our experience of space-time curving and distorting in the
presence of matter and energy.
-
- This curved space sets the rules for how
energy and matter move. Even though light travels in a straight line, light
moving through a highly curved region of space-time, like the space around
enormous galaxies, also travels in a curve, bending around the galaxy and
splaying out into a halo.
-
- What this halo looks like depends on the
strength of the galaxy's gravity and the perspective of the observer. In this
case, Earth, the lensing galaxy and the quasar have aligned to perfectly
duplicate the quasar's light, arranging them along a so-called “Einstein ring”.
-
- The lens was discovered in 2021 by the “Dark
Energy Spectroscopic Instrument”, which is attached to the telescope at Kitt
Peak National Observatory in Arizona.
After the lens's discovery, the astronomers performed follow-up analyses
with the “Multi-Unit Spectroscopic Explorer” at the Very Large Telescope in
Chile, and confirmed that they had discovered an Einstein cross.
-
- Astronomers have identified hundreds of
Einstein rings, and they're not sought after only for the pretty pictures they
make. As the rings work to magnify the light they bend, reconstructing the
light smears into their original, pre-bent forms can enhance the details
astronomers can spot in very distant galaxies.
-
- The extent to which light bends depends on
the strength of the gravitational field of the object that bends it, Einstein
rings can act as a cosmic scale for gauging the masses of galaxies and black
holes. Studying the distant light warping around these rings can even help
scientists glimpse objects that would otherwise be too dark to be seen on their
own, such as black holes or wandering exoplanets.
-
- Albert Einstein’s theory of general
relativity has been remarkably successful in describing the gravity of stars
and planets, but it doesn’t seem to apply perfectly on all scales. The James Webb Space Telescope has produced
the deepest and sharpest infrared image of the distant universe to date.
-
- Everything in the universe has gravity and
feels it too. Yet this most common of all fundamental forces is also the one
that presents the biggest challenges to physicists. Albert Einstein’s theory of
general relativity has been remarkably successful in describing the gravity of
stars and planets, but it doesn’t seem to apply perfectly on all scales.
-
- General relativity has passed many years of
observational tests, from Eddington’s measurement of the deflection of starlight
by the Sun in 1919 to the recent detection of gravitational waves. However,
gaps in our understanding start to appear when we try to apply it to extremely
small distances, where the laws of quantum mechanics operate, or when we try to
describe the entire universe at large distances.
-
- Quantum theory predicts that empty space,
the vacuum, is packed with energy. We do not notice its presence because our
devices can only measure changes in energy rather than its total amount.
-
- However, according to Einstein, the vacuum
energy has a repulsive gravity, it pushes the empty space apart. Interestingly,
in 1998, it was discovered that the expansion of the universe is in fact
accelerating.
-
- However, the amount of vacuum energy, or
dark energy as it has been called, necessary to explain the acceleration is
many orders of magnitude smaller than what quantum theory predicts.
-
- Hence the big question, dubbed “the old
cosmological constant problem”, is whether the vacuum energy actually gravitates,
exerting a gravitational force and changing the expansion of the universe.
-
- Then why is its gravity so much weaker than
predicted? If the vacuum does not gravitate at all, what is causing the cosmic
acceleration?
-
- We don’t know what dark energy is, but we
need to assume it exists in order to explain the universe’s expansion.
Similarly, we also need to assume there is a type of invisible matter presence,
dubbed dark matter, to explain how galaxies and clusters evolved to be the way
we observe them today.
-
- These assumptions are baked into
scientists’ standard cosmological theory, called the “lambda cold dark matter”
(LCDM) model, suggesting there is 70% dark energy, 25% dark matter and 5%
ordinary matter in the cosmos. And this model has been remarkably successful in
fitting all the data collected by cosmologists over the past 20 years.
-
- But the fact that most of the universe is
made up of dark forces and substances, taking odd values that don’t make sense,
has prompted many physicists to wonder if Einstein’s theory of gravity needs
modification to describe the entire universe.
-
- A new twist appeared a few years ago when it
became apparent that different ways of measuring the rate of cosmic expansion,
dubbed the Hubble constant, give different answers, a problem known as the
Hubble tension.
-
- The disagreement, or tension, is between two
values of the Hubble constant. One is the number predicted by the LCDM
cosmological model, which has been developed to match the light left over from
the Big Bang (the cosmic microwave background radiation). The other is the
expansion rate measured by observing exploding stars known as supernovas in
distant galaxies.
-
- Many theoretical ideas have been proposed
for ways of modifying LCDM to explain the Hubble tension. Among them are
alternative gravity theories.
-
- General relativity describes gravity as the
curving or warping of space and time, bending the pathways along which light
and matter travel. Importantly, it predicts that the trajectories of light rays
and matter should be bent by gravity in the same way.
-
- To find out whether general relativity is
correct on large scales simultaneous investigations of three aspects of it.
These were the expansion of the universe, the effects of gravity on light and
the effects of gravity on matter.
-
- Using a statistical method known as the
“Bayesian inference”, they reconstructed the gravity of the universe through
cosmic history in a computer model based on these three parameters. We could
estimate the parameters using the cosmic microwave background data from the
Planck satellite, supernova catalogues as well as observations of the shapes
and distribution of distant galaxies by the SDSS and DES telescopes. We then compared
our reconstruction to the prediction of the LCDM model (essentially Einstein’s
model).
-
- We found interesting hints of a possible
mismatch with Einstein’s prediction, albeit with rather low statistical
significance. This means that there is nevertheless a possibility that gravity
works differently on large scales, and that the theory of general relativity
may need to be tweaked.
-
- This study also found that it is very
difficult to solve the Hubble tension problem by only changing the theory of
gravity. The full solution would probably require a new ingredient in the
cosmological model, present before the time when protons and electrons first
combined to form hydrogen just after the Big Bang, such as a special form of
dark matter, an early type of dark energy or primordial magnetic fields.
-
- This study has demonstrated that it is
possible to test the validity of general relativity over cosmological distances
using observational data. While we haven’t yet solved the Hubble problem, we
will have a lot more data from new probes in a few years.
-
- We should be able to use these statistical
methods to continue tweaking general relativity, exploring the limits of
modifications, to pave the way to resolving some of the open challenges in
cosmology.
-
-
August 5, 2023 EINSTEIN
CROSS - a new model for the Universe? 4110
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Saturday, August 5, 2023 ---------------------------------
No comments:
Post a Comment