Podcaster: Richard Drumm
Title: Space Scoop: Galaxies Spin Faster as They Get Older
Organization:365 Days Of Astronomy
Link : astrosphere.org ; http://unawe.org/kids/unawe1707/
Description: Space scoop, news for children
Our understanding of Saturn’s rings is still evolving. A team of researchers using observations made in 2008 have managed to measure the brightness and temperature of Saturn’s rings in more detail than ever. More detail in mid-infrared images from the ground, that is.
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Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is the 365 Days of Astronomy Podcast. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Galaxies Spin Faster as They Get Older
How many cosmic objects can you name in 10 seconds?
Ready? Set. Go!
Did you get any of the following: planets, moons, stars, galaxies, asteroids, comets, satellites, nebulae, black holes. Hmmm?
All of these objects, everything on Earth, everything ever observed with all of our tools & telescopes, eyeballs & instruments – makes up less than 5% of the Universe.
The rest of the Universe is made of two very mysterious, invisible materials called ‘dark energy’ and ‘dark matter’.
Dark matter doesn’t shine like stars or reflect light like planets, or even absorb light like cosmic dust. We can only detect dark matter through its gravitational effect on other objects, such as spiral galaxies.
Like the wind on a fall day, you can’t see it but you can sure see how it makes the leaves blow around.
Like the moon and planets, spiral galaxies spin, although it takes them hundreds of millions of years to go around once.
We would expect that stars at the outer edges of these galaxies would move much slower than stars closer to the centre. In the same way that planets farther from the Sun move slower than those in the inner Solar System.
But in galaxies it’s a different story.
Because of the large amount of dark matter in galaxies, the outer edges of galaxies move faster than expected.
The Swiss astronomer Fritz Zwicky discovered in 1933 that the Coma Cluster of galaxies appeared to have 400 times greater mass than the light coming from the cluster indicated should be there.
He figured that there was a great deal of “dunkle Materie”, or dark matter, present to account for the motion of the galaxies. The galaxies were moving at escape velocity such that the cluster would come apart.
But since the cluster was obviously not flying apart there must be something holding it together.
Today’s recalculation of the result is less than the 400 figure, but it’s still obvious that dark matter is predominant.
That was a calculation based on galaxies in a cluster of galaxies, but what about the rotational movement of a single galaxy?
Enter astronomer Vera Rubin.
She and instrument-maker Kent Ford in the 1970s started working on the rotation of galaxies as part of a larger inquiry into the expansion of the Universe.
By the 1980s the two had abandoned the expansion of the Universe angle and worked on galaxy rotation as an area of interest in and of itself.
You see, back in 1939 American astronomer Horace Babcock had found that the Andromeda galaxy rotated oddly. He didn’t think it was due to dark matter, though.
But the old reports of his findings aroused Rubin & Ford’s curiosity.
Now, in the solar system most of the mass is located in the center, in the Sun. As a result of gravity’s effects falling off in accordance with the inverse square law, planets farther out move more slowly than those closer in.
But in the case of the easy-to-study and close by Andromeda galaxy, it was clear that the outer parts of the galaxy were spinning so fast that the galaxy should just fly apart.
Since that galaxy clearly isn’t flying apart, there must be more mass in the outer reaches of the galaxy, unlike the center-heavy mass distribution of the solar system.
Rubin & Ford showed that galaxies had to have 6 times more mass than the light coming from them shows. It had to be dark matter and it wasn’t located primarily in the galactic core.
So galaxies rotate fast at the outer edges like an LP record spinning on a turntable and dark matter holds the galaxy together and keeps it from flying apart.
This relationship has held up for all galaxies that are close enough for the measurements to be made with the instruments that astronomers had to work with.
However, astronomers, now using new instruments, have looked at galaxies that are very far away and have just found that when the Universe was young that relationship wasn’t the case.
That’s right, you heard that correctly. When the Universe was much younger galaxies spun differently!
They used the KMOS and SINFONI spectrographs at the ESO’s Very Large Telescope at Paranal Observatory in Chile to study 6 distant galaxies in particular. Galaxies from the early Universe.
When looking at these ancient galaxies they found that their outer edges moved more slowly than regions closer to the centre, just like planets do around our Sun.
This tells us that the first galaxies didn’t contain as much dark matter as those we see today. In the early Universe, galaxies were mostly made up of normal material, called baryonic material, like stars, cosmic gas and planets. And the matter was located mostly in the center of the galaxies.
Whereas galaxies today are dominated by invisible dark matter that’s in a halo around the galaxy and not mostly in the center.
The dark matter was likely there, but wasn’t hovering around the galaxies just yet. It was probably in the filaments of matter that ran between the galaxies back at those early times.
Hey Here’s A Cool Fact:
Our Milky Way Galaxy takes about 250 million years to complete one full turn nowadays. Back in the early Universe the outer parts of the galaxy would have rotated much more slowly.
Not that anybody would’ve noticed, though.
Thank you for listening to the 365 Days of Astronomy Podcast!
End of podcast:
365 Days of Astronomy
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