Space Fan News #77: Dark Energy is Real; Dark Matter Shows Itself - Finally


Uploaded by tdarnell on 14.09.2012

Transcript:
Hello Space Fans and welcome to another edition of Space Fan News.
Dark News Everyone! It appears we're getting closer to understanding BOTH dark energy and
dark matter.
First, dark energy.
According to a team of astronomers at the University of Portsmouth and LMU University
Munich, dark energy, whatever it is, is real.
After conducting a two-year study, the scientists concluded that the likelihood of the existence
of dark energy stands at 99.996 per cent.
Now for those of you who don't know, the universe is accelerating as it expands, this was discovered
a while back by carefully measuring redshifts of Type 1a supernovae, this was such a huge
discovery that the guys who made it got the Nobel Prize for it last year.
This was a really surprising discovery, everyone assumed the universe would be gradually slowing
down after the Big Bang, but that's not what we found. The universe is accelerating.
Now, for this to be happening, one of two things is going on: either something is pushing
everything apart, there must be a force causing everything to not just expand, but to go faster
over time…
Or there's something about our current theories of gravity we don't understand on large scales
and we need to go back to the drawing board.
Now since the discovery of the acceleration of the expansion of the universe, there has
been a lot of controversy over what's going on. Many astronomers disput the idea of a
dark energy pushing everything apart.
Well this week, this group of astronomers claim to have settled it. They are 99.996
percent sure that dark energy exists, that's the same level of certainty CERN scientists
claimed for the discovery of the Higgs Boson earlier this year.
They still don't know what it is, but they are as sure it's there as we are of the Higgs
Boson.
So what makes them so sure dark energy is real?
There are many other techniques that have been used to confirm the reality of dark energy
but they are indirect measurements of the accelerating Universe, not direct observations.
This research says that you can see dark energy through something called the Integrated Sachs
Wolfe effect in the CMB.
The Cosmic Microwave Background is the radiation of the residual heat of the Big Bang and is
seen all over the sky.
In 1967 Sachs and Wolfe proposed that light from this radiation would become slightly
bluer as it passed through the gravitational fields of lumps of matter, an effect known
as gravitational redshift.
In 1996, this idea was taken to the next level and it was suggested that astronomers could
look for these small changes in the energy of the light by comparing the temperature
of the radiation in the CMB with maps of nearby galaxies.
If dark energy didn't exist, then there would be no correspondence between these the distant
cosmic microwave background and relatively closer distribution of galaxies.
But if dark energy did exist, then we would see a strange, counter-intuitive effect where
the cosmic microwave background photons would gain energy as they travelled through large
lumps of mass.
I know, it's weird, but as the CMB radiation travels through material, it gains energy
under this effect.
So to test this, you look at photons from the CMB while they travel through nearby galaxies
on their way to us and look for this effect. If dark energy is out there, we would see
the CMB photons blue shifted as they gained energy through the Sachs Wolfe Effect.
Here's a diagram that shows what I'm talking about.
Here are the maps they used in the comparison, they are in increasing order of distance from
the Earth. On the left are are six shells containing maps of the millions of distant
galaxies used in the study - these are galaxies in between us and the background CMB. These
maps are produced using different telescopes in different wavelengths and are colour-coded
to show denser clumps of galaxies as red and under-dense regions as blue.
The last, largest shell shows the temperature of the cosmic microwave background from the
WMAP satellite (red is hot, blue is cold)
Comparing the hot and cold temperatures of the CMB with the clumps of galaxies in the
foreground, they found (at 99.996% significance) very small correlations between them.
So there you go, dark energy is real and backed up by observations, it appears we have a direct
method for finding out that it's there. Everyone is hoping for more confirmation with future
measurements of the CMB and in the new galaxy surveys that are taking place now.
I'll keep you posted.
Next, as if that wasn't enough, this week astronomers announced a technique for finding
dark matter, and once again, to find it, we look at the CMB.
Astronomers looking at the all-sky CMB survey taken by the Planck Space telescope have observed
a very unique emission of radio radiation from the center of our galaxy.
Using different methods to separate the signal for very broad range of wavelengths, the Planck
team determined that the radiation has a spectrum which has the same form as that of synchrotron
emission, which is created when electrons and positrons circulate at high energies around
the lines of the Magnetic Field in the center of the galaxy.
This radiation, they believe, could come from dark matter,
Here's why:
Early in the 20th Century, Niels Bohr and others have predicted that dark matter may
consist of very heavy particles that are around 10 times as heavy as the Higgs particle, or
1,000 times heavier than a proton. Of course as we all know, they have very irritating
property that they do not interact with ‘normal’ matter particles, they don't even interact
with each other.
Most theories predict that there should be a very high concentration of dark matter at
the center of galaxies and even though they don't interact with anything, there's no reason
to think that they they can't become so concentrated such that every once in a while, they will
collide.
These collisions would produce electrons and positrons (particles that we can see) and
because they are charged, will start to rotate around the magnetic field at the center of
our galaxy and when they do this, they produce this signature synchrotron radiation.
Up until now, It has simply not been possible to observe this radiation in much detail before,
previous instruments have just not been sensitive enough. But with Planck, this unusual radiation
is seen very clearly.
According to Pavel Naselsky, professor of cosmology at the Discovery Center at the Niels
Bohr Institute at the University of Copenhagen, “The radiation cannot be explained by the
structural mechanisms in the galaxy and it cannot be radiation from supernova explosions.
I believe that this could be proof of dark matter. Otherwise, we have discovered absolutely
new (and unknown for physics) mechanism of acceleration of particles in the Galactic
centre”
He also says he is expecting more exciting results in the next few months.
I'll keep you posted on that too.
Well, that's it for this dark edition of Space Fan News, thank you for watching and as always,
Keep Looking Up.