Hello Space Fans and welcome to this week's final installment covering interesting news
from the American Astronomical Society.
And, for those who like round numbers, this just so happens to be the 50th episode of
Space Fan News.
Unbelievable.
Have you ever wondered how they know how much dark energy is in the universe?
Well to start you need to look at the universe.
As much of it as you can all at once because embedded in the universe is something called
Baryonic Acoustic Oscillations and from those oscillations we can determine the amount of
dark energy we have.
Baryonic is just a fancy word for ordinary matter and acoustic oscillations is a fancy
word for sound waves.
So we're basically talking about the movement of ordinary matter along sound wave, a lot
like how water moves in an ocean.
These sounds waves are responsible for the way in which matter is distributed throughout
the universe, and the only way to see them is to look everywhere and measure where all
the galaxies are throughout the cosmos.
Since 2000, the Sloan Digital Sky Survey has been doing just that and have so far surveyed
well over a quarter of the night sky and produced the largest color map of the universe in three
dimensions to date.
Today the Sloan collaboration released this map of 900,000 galaxies covering 14,000 square
degrees of the sky.
Every one of these 900,000 green dots is a galaxy and was imaged five times at different
wavelengths.
From those images, astronomers were able to calculate the distance to the galaxy and then
the coordinates were placed placed in the map.
The redshift range here goes from 0.25 to 0.75 z so this map is showing where all the
galaxies are or have been from present, located near the center, to about six billion years
ago, located around the edge.
And we are at the center because that's where the observations were taken.
You can see from this map that there is better coverage at smaller z than farther out, and
the gaps in the outer part of the map are where galaxies either weren't measured or
couldn't be seen by the Sloan telescope, which is located in New Mexico.
Most of the 900,000 galaxies here are ancient red galaxies which contain primarily slow
burning red stars.
These galaxies are so old that virtually all of the faster burning brighter stars have
long since extinguished, but they are exceptionally bright and visible at great distances.
The galaxies chosen for this study populate the largest volume of space ever used for
galaxy clustering measurement.
Which brings us to how they measure dark energy.
Just after the Big Bang, the universe was hot and dominated by photons.
By about 50,000 years later, the amount of radiation and matter was equal and only then
could structure begin to form.
But the big bang caused the universe to oscillate affecting this early hot soup of radiation
and matter.
These cosmic sound waves move ordinary atoms much like waves move water in the ocean, and
are still going on today, ultimately affecting where all of these galaxies are in the universe
today.
The universe cooled some 300,000 years later, allowing matter to form into atoms, then stars,
then galaxies.
Where these first galaxies formed are imprinted on the cosmic microwave background.
The red areas are warmer and defines where matter in the universe was initially located.
This is the starting point for all galaxies the ever existed.
And this is where they are from six billion years ago to present.
Looking at where all matter is located is a form of measurement of the sound waves of
the universe.
But the universe is expanding, presumably being pushed by dark energy, this will have
a marked effect on the shape of the sound waves, and by measuring their movement throughout
the history of the universe, we get an idea of how much force was required to alter the
shape of the acoustic oscillations.
And that force leads us directly to the amount of energy available to affect the shape of
the universe.
Measuring these sound waves is one of the most reliable and independent ways of measuring
dark energy.
But to do it, you gotta look at everything.
Since the time of the COBE satellite, we've had a good baseline for these sound waves
from the early universe.
But this study provided the most comprehensive measurement of where they are now and in the
relatively recent past.
Any difference between this map and the cosmic microwave radiation map will be due to the
effects of dark energy.
As dark energy stretches the universe against the gravity of dark matter, it places galaxies
at a larger distance from us, and their oscillations are different from the past.
Carefully comparing these oscillations from the early universe to the ones associated
with these galaxies gives us the amount of dark energy everywhere.
So what's the answer?
73% of the universe is made up of dark energy, with an error of only two percent.
That's the most accurate measurement yet.
And THAT is just like downtown.
Next, NASA announced that it will launch NuSTAR.
NuSTAR stands for Nuclear - not nucular - Spectroscopic Telescope Array and will launch this August.
It is designed to image the sky in high-energy X-rays.
NuSTAR will carry the first high-energy X-ray focusing telescopes into orbit, and will provide
a deeper and clearer view of energetic bodies and events like black holes and supernovae
than any previous instrument in orbit now.
Since this is an X-ray telescope it needs to be above the atmosphere and X-rays are
notoriously difficult to focus - they just go through most mirrors - we've only recently,
with the Einstein Observatory, figured out how to properly do it.
Basically, x-rays are focused by glancing them off of reflective surfaces at very shallow
angles, you can't just bounce back an x-ray.
In NuSTAR, X-rays will be collected through concentric rings, with two little bends in
them to bring all the x-rays to a focus on the image plane where special.
high resolution detectors will take pictures.
This technique promises to provide some pretty stunning images of black holes and supernovae,
the likes of which we've never seen before, so look for this spacecraft to join our already
mighty pantheon of space telescopes in orbit in August of this year.
Whew!
I don't know about you, I'm exhausted, but in a good way.
This has been a wonderful week of discovery and I really hope you guys got something out
of it because I had a lot of fun making these.
I'd like to thank Dr. Alberto Conti and Dr. Jason Kalirai from the Space Telescope Science
Institute for taking the video footage for these episodes, and I'll see you guys all
next Friday at our regular time.
Thank you all for watching and, as always, Keep Looking Up!