- 4277 - DARK MATTER - gravitational lensing? - Astronomers are learning more about Dark Matter's distribution throughout the Universe. Since we can’t see it directly, observers need to use indirect methods to detect it. One way is through gravitational lensing. Another is by looking for emissions from hydrogen gas associated with small-scale dark matter structures in the Universe.
------------------- 4277 - DARK MATTER - gravitational lensing?
- The Atacama Large
Millimeter Array in Chile was used to study a distant gravitational lens system
called “MG J0414+534”. A massive foreground galaxy is bending and distorting
the light from a distant quasar that lies some 11 billion light-years away. The
result is four seperate images of the quasar.
-
- They found some
strange anomalies in the images. They are actually variations in the
distribution of dark matter along the line of sight between us and the quasar.
The gravitational lens magnified the fluctuations and analysis of the data
allowed astronomers to map the fluctuations down to a scale of 30,000
light-years.
-
- Throughout the
universe, dark matter is associated with massive galaxies and galaxy clusters.
However, small-scale clumps and distributions aren’t as well understood. So,
astronomers want to find ways to map the smaller concentrations of it.
Gravitational lensing provides one way to do that.
-
- In the case of MG
J0414+0534, the positions and shapes of the lensed quasar images look a little
strange. They don’t fit the model of gravitational lensing predicted when you
plug in the numbers for the galaxy and its associated dark matter component.
-
- The fluctuations
indicate that there’s a gravitational lensing effect from the smaller
concentrations, in addition to that of the galaxy and its dark matter shell. In
this case, there are spatial fluctuations in the density of dark matter down to
a size of about 30,000 light-years. That’s way smaller than what the scientists
term the “cosmological scale” for larger concentrations of several tens of
billions of light-years.
-
- The such smaller
concentrations work with predictions made about cold dark matter (CDM).
Essentially, it says that dark matter clumps exist within galaxies, but also
can populate intergalactic space. The gravitational lensing effects due to the
clumps of dark matter found in this study are so small that it is extremely
difficult to detect them alone. That’s why the team used ALMA to detect the
fluctuations. It can provide very high-resolution radio observations of
fluctuations caused by the smaller concentrations of dark matter.
-
- Astronomers used a
giant radio telescope, the Five-Hundred-Aperture Spherical Radio Telescope
(FAST) in China to look at another interesting dark matter-related object that
lies near the galaxy M94. The system, which they call “Cloud-9, is a source of
21-centimeter radio emissions from cold neutral interstellar hydrogen.
-
- Cloud-9 appears
to be relatively starless. The most
popular model of cold dark matter, galaxies form in the centers of halos of a
certain size. The models also show that there should be a number of collapsed
dark matter halos. And, there’s no reason why there shouldn’t be smaller
“blobs” throughout the Universe. Many
low mass versions of dark matter halos remain dark or starless even after
billions of years of cosmic evolution.
-
- Cloud-9 will
require a lot more study, higher-resolution observations are needed. For one
thing, its distance really needs to be pinned down. So, future observations
using the MeerKAT telescope, the Very Large Array, or even the FAST in China
could be made. Follow-up observations using the Hubble Space Telescope could
help astronomers find out whether or not Cloud-9 definitely has any stellar
components.
-
- This mysterious
cloud could have a galaxy at its heart, but that it’s too faint to be detected.
Certainly in the early Universe, galaxies and stars formed as a result of
gravitational growth of density fluctuations in dark matter.
-
- Hydrogen and
helium (the building blocks of stars) were attracted by the clumps of dark
matter and began to form stars. However, that applies to the distribution of
dark matter at the galaxy and larger scales.
-
- Accumulations of
dark matter on smaller scales, such as with Cloud-9, really aren’t well
understood. That’s why further observations of Cloud-9 will definitely help
determine the full extent of its dark matter content. They could also shed some
light on how galaxies form at the small scale of smaller dark matter
accumulations.
-
-
December 15, 2023
DARK MATTER -
gravitational lensing? 4273
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