- 3979
- UNIVERSE -
first light? By measuring the
Cosmic Microwave Background for redshift and comparing these to local distance
measurements (using variable stars and supernovae), astronomers have sought to
measure the rate at which the universe is expanding.
-
----------------------- 3979 - UNIVERSE - first light?
- In the
1960s, astronomers began noticing a pervasive microwave background visible in
all directions. This became known as the “Cosmic Microwave Background” (CMB),
the existence of this relic radiation confirmed the Big Bang theory that all
matter was condensed onto a single point of infinite density and extreme heat
that began expanding 13.8 billion years ago.
-
- Scientists
observed that the rotational curves of galaxies were much higher than their
visible mass suggested. This meant that either Einstein's Theory of General
Relativity was wrong or the universe was filled with a mysterious, invisible
mass.
-
- Astronomers
are using improved measurements of parameters that describe the very early
universe by monitoring the light that emerged during "Cosmic Dawn"
(when the universe was only 380,000 years old), which is visible today as the
CMB.
-
- According to
the cosmological model,the “Lambda Cold Dark Matter (LCDM)”, Dark Matter accounts for 85% of the mass in
the cosmos. Unfortunately, it doesn't interact with normal
("luminous") matter via electroweak or strong nuclear forces, only
with gravity (the weakest of the fundamental forces).
-
- To track
down this illusive and "invisible" mass, the ACT collaboration uses
the “Atacama Cosmology Telescope” (ACT), a custom-built six-meter (20-foot)
millimeter-wave telescope located in northern Chile.
-
- Astronomers
used data from the ACT's Data Release 6 (DR6), which consisted of five seasons
of CMB temperature and polarization observations. These light readings were
essentially used to backlight all of the matter between the present day and the
Big Bang ( 13.8 billion years ago).
-
- It's a bit
like silhouetting, but instead of just having black in the silhouette, you have
texture and lumps of dark matter, as if the light were streaming through a
fabric curtain that had lots of knots and bumps in it. The CMB image is a
snapshot of what the universe was like in a single epoch, about 13 billion
years ago, and now this is giving us the information about all the epochs
since.
-
- The
full-sky image is based on data collected by the “Wilkinson Microwave
Anisotropy Probe” (WMAP) between 2001 and 2003. This mission (which remained in
operation until 2010) built on the previous work by the “Cosmic Background
Explorer” (COBE), which collected data on the CMB from 1989 to 1993.
-
- Then came
the ESA's “Planck” satellite, which measured the CMB from 2009 to 2013 to map
tiny temperature fluctuations. The increasingly accurate maps that resulted
have provided insight into the evolution of the cosmos by showing what its
initial conditions were.
-
- This latest
map has taken that research a step further by using it to measure how the
structure of matter has evolved since, 85% of which is Dark Matter.
-
- To
visualize the presence and distribution of this mysterious mass, the research
team examined how its gravity affected the curvature of spacetime between the
CMB and Earth. This effectively showed how large collections of mass (both
visible and invisible) altered the path its light followed as it traveled for
billions of light-years distance (and billions of years time) to reach us.
-
- The astronomers
tracked how the gravitational pull of massive dark matter structures can warp
the CMB on its 14-billion-year journey to us, just as antique, lumpy windows
bend and distort what we can see through them. The resulting map revealed the
"scaffold" of Dark Matter that holds visible matter and surrounds and
connects galaxies and galaxy clusters.
-
- This led to
the universe's large-scale structure, referred to as the "Cosmic
Web". This map breaks with convention by measuring the distribution of
matter in our universe, not in terms of light but in terms of mass.
-
- This is
stunning evidence that we understand the story of how structure in our universe
formed over billions of years, from just after the Big Bang to today.
Remarkably, 80% of the mass in the universe is invisible. By mapping the dark
matter distribution across the sky to the largest distances, our ACT lensing
measurements allow us to clearly see this invisible world.
-
- It provides
measurements that show that both the 'lumpiness' of the universe, and the rate
at which it is growing after 14 billion years of evolution, are just what you'd
expect from our standard model of cosmology based on Einstein's theory of
gravity.
-
- These
results could also provide new insight into the so-called "Crisis in
Cosmology," where light measurements using the CMB vs. local stars produce
different values. Also known as the "Hubble Tension," this disparity
suggests that Dark Matter was not "lumpy" enough and that the standard
model of cosmology (LCDM) may be incorrect.
-
- However,
the ACT team's latest results precisely assessed the size and distribution of
these lumps and determined that they were perfectly consistent with the LCDM
model.
-
- The CMB is
famous already for its unparalleled measurements of the primordial state of the
universe, so these lensing maps, describing its subsequent evolution, are
almost an embarrassment of riches. We now have a second, very primordial map of
the universe.
-
- We have an
extraordinary opportunity to use these different data sets together. This map
includes all of the dark matter, going back to the Big Bang, and the other maps
are looking back about 9 billion years, giving us a layer that is much closer
to us. We can compare the two to learn about the growth of structures in the
universe. The two approaches are getting
different measurements.
-
- While the
ACT was decommissioned in September 2022 (after 15 years in operation), the
data it gathered still inspire new research and breakthroughs. More papers
presenting results from the final set of observations in the DR6 are expected
soon, and the Simons Observatory will conduct future observations from the same
sight.
-
- These will
be done using a new telescope scheduled to begin operations in 2024 that will
be capable of mapping the sky almost ten times as fast as the ACT. Perhaps we
can look forward to all-sky surveys that map the distribution of Dark Matter
going back to the beginning of the cosmos.
-
April 30, 2023 UNIVERSE -
first light?
3979
----------------------------------------------------------------------------------------
----- 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” -----------
--------------------- --- Monday, May 1, 2023
---------------------------
-
No comments:
Post a Comment