- 3987 - DARK MATTER - controls universe expansion? The map including 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.
------------ 3987 - DARK MATTER - controls universe expansion?
- Astronomers
began noticing a pervasive microwave background visible in all directions
starting in 1960. It became known as the “Cosmic Microwave Background” (CMB),
the existence of this relic radiation confirmed the Big Bang theory, which
posits that all matter was condensed onto a single point of infinite density
and extreme heat that began expanding ca. 13.8 billion years ago.
-
- By measuring
the CMB 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.
-
- Around the
same time, 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 causing rotations to be constant with exanding
radius.
-
- Astronomers
have used background light from the CMB to create a new map of Dark Matter
distribution that covers a quarter of the sky and extends deep into the cosmos.
This map confirms General Relativity and its predictions for how mass alters
the curvature of spacetime.
-
- The ACT is
an international consortium of more than 160 scientists from the U.S., the
U.K., Canada, France, Germany, Italy, Chile, Switzerland, Japan, South Africa,
and NASA's Goddard Space Flight Center.
-
- Their goal
is to provide 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.
-
- By
comparing this to measurements of the local universe, astronomers and
cosmologists hope to learn more about how it evolved. According to the predominant cosmological model,
the Lambda Cold Dark Matter (LCDM) model, Dark Matter accounts for 85% of the
mass in the cosmos.
-
- Dark Matter
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.
-
- With five
seasons of CMB temperature and polarization observations the readings were used to backlight all of the
matter between the present day and the Big Bang ( 13.8 billion years ago).
-
- It is a
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.
-
- This famous
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.
-
- 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 (and billions of years) to reach us.
-
- They
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". The map also breaks with convention by measuring
the distribution of matter in our universe, not in terms of light but in terms
of mass.
-
- 80% of the
mass in the universe is invisible. By mapping the dark matter distribution
across the sky to the largest distances,
ACT lensing measurements allow us to clearly see this invisible world.
-
- These
results could 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..
-
- The map including 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.
-
- While the
ACT was decommissioned in September 2022 (after 15 years in operation), the
data it gathered still inspire new research and breakthroughs. 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 universe.
-
May 7, 2023 DARK
MATTER - controls universe expansion? 3987
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--------------------- --- Sunday, May 7, 2023
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