“Dark
flow” is no fluke, suggests a new study that strengthens the case for
unknown, unseen “structures” lurking on the outskirts of creation.
In 2008
scientists reported the discovery of hundreds of galaxy clusters streaming in
the same direction at more than 2.2 million miles (3.6 million kilometers) an
hour.
scientists reported the discovery of hundreds of galaxy clusters streaming in
the same direction at more than 2.2 million miles (3.6 million kilometers) an
hour.
This
mysterious motion can’t be explained by current models for distribution of mass
in the universe. So the researchers made the controversial suggestion that the
clusters are being tugged on by the gravity of matter outside the known
universe.
mysterious motion can’t be explained by current models for distribution of mass
in the universe. So the researchers made the controversial suggestion that the
clusters are being tugged on by the gravity of matter outside the known
universe.
The Coma
Galaxy Cluster, which appears to participate in the mysterious motion known as
dark flow.
Galaxy Cluster, which appears to participate in the mysterious motion known as
dark flow.
Now the same
team has found that the dark flow extends even deeper into the universe than
previously reported: out to at least 2.5 billion light- years from Earth.
After using
two additional years’ worth of data and tracking twice the number of galaxy
clusters, “we clearly see the flow, we clearly see it pointing in the same
direction,” said study leader Alexander Kashlinsky, an astrophysicist at
NASA’s Goddard Space Flight Center (DSFC) in Maryland.
two additional years’ worth of data and tracking twice the number of galaxy
clusters, “we clearly see the flow, we clearly see it pointing in the same
direction,” said study leader Alexander Kashlinsky, an astrophysicist at
NASA’s Goddard Space Flight Center (DSFC) in Maryland.
“It
looks like a very coherent flow.”
looks like a very coherent flow.”
The find
adds to the case that chunks of matter got pushed outside the known universe
shortly after the big bang—which in turn hints that our universe is part of
something larger: a multiverse.
adds to the case that chunks of matter got pushed outside the known universe
shortly after the big bang—which in turn hints that our universe is part of
something larger: a multiverse.
Kashlinsky
and colleagues first noticed the dark flow when studying the way gas in galaxy
clusters interacts with the cosmic microwave background radiation. This burst
of light is thought to have been released just 380,000 years after the big bang
and now permeates the universe.
and colleagues first noticed the dark flow when studying the way gas in galaxy
clusters interacts with the cosmic microwave background radiation. This burst
of light is thought to have been released just 380,000 years after the big bang
and now permeates the universe.
Data from
the Wilkinson Microwave Anisotropy Probe (WMAP) can show the minute temperature
changes created as the cosmic microwave background radiation moves through
gases in galaxy clusters.
the Wilkinson Microwave Anisotropy Probe (WMAP) can show the minute temperature
changes created as the cosmic microwave background radiation moves through
gases in galaxy clusters.
These gases
scatter light from the cosmic microwave background radiation as it passes
through the clusters, similar to the way Earth’s atmosphere can scatter
starlight, making some stars twinkle.
scatter light from the cosmic microwave background radiation as it passes
through the clusters, similar to the way Earth’s atmosphere can scatter
starlight, making some stars twinkle.
But the
clusters are also moving relative to the background radiation, so the scattered
light gets distorted further by the Doppler effect. This distortion appears in
the form of temperature shifts in WMAP data, which can reveal the clusters’
direction and speed.
clusters are also moving relative to the background radiation, so the scattered
light gets distorted further by the Doppler effect. This distortion appears in
the form of temperature shifts in WMAP data, which can reveal the clusters’
direction and speed.
“It is
very difficult to isolate [the temperature change] for each individual
cluster,” Kashlinsky said, so the original study had examined 700
clusters.
very difficult to isolate [the temperature change] for each individual
cluster,” Kashlinsky said, so the original study had examined 700
clusters.
The new
study is based on the collective motion of about 1,400 galaxy clusters, and
seeing dark flow with the greater number of clusters gives the researchers more
confidence in their result.
study is based on the collective motion of about 1,400 galaxy clusters, and
seeing dark flow with the greater number of clusters gives the researchers more
confidence in their result.
In addition,
the team tested their analysis method by comparing the x-ray brightness of
certain clusters with the strength of temperature changes seen in the WMAP data.
Brighter clusters—those with more hot gases—would be expected to have greater
effects on the cosmic microwave background, and that’s what the new study
confirmed.
the team tested their analysis method by comparing the x-ray brightness of
certain clusters with the strength of temperature changes seen in the WMAP data.
Brighter clusters—those with more hot gases—would be expected to have greater
effects on the cosmic microwave background, and that’s what the new study
confirmed.
Kashlinsky
speculates that the dark flow extends “all the way across the visible
universe,” or about 47 billion light-years, which would fit with the
notion that the clusters are being pulled by matter that lies beyond known
horizons.
speculates that the dark flow extends “all the way across the visible
universe,” or about 47 billion light-years, which would fit with the
notion that the clusters are being pulled by matter that lies beyond known
horizons.
Dark flow,
he said, “Would be much more difficult to explain theoretically if it
extended [2.5 billion light-years] and then just stopped.”
he said, “Would be much more difficult to explain theoretically if it
extended [2.5 billion light-years] and then just stopped.”
Findings are
reported in the March 20 issue of The Astrophysical Journal Letters.
reported in the March 20 issue of The Astrophysical Journal Letters.
