Date: April 15, 2012
Title: Encore : The Secrets of Star Birth
Podcaster: Daniel Pendick
My blog: geeked.gsfc.nasa.gov
This podcast originally aired on September 18, 2010
Description: Everyone knows where babies come from — but what about baby stars? NASA science writer and blogger Daniel Pendick talks to astrophysicist Jennifer Wiseman about the hidden process of star formation and what we will learn from new observatories and instruments now coming online. The Herschel Space Observatory, for example, recently confirmed that stars form along ragged filaments of collapsing gas cloud, “like beads on a string.” And a massive radio telescope under construction in the Atacama Desert of Chile will give us our first close long at the planet-forming zone of young solar systems.
Bio: Daniel Pendick is a science writer and blogger at Goddard Space Flight Center. His “Geeked On Goddard” blog takes an irreverent insider’s look at science and engineering at Goddard. His writing has appeared in Astronomy, New Scientist, Earth, Scientific American Presents, and many other science and medical publications and websites.
Jennifer Wiseman, a NASA astrophysicist, currently heads the Laboratory for Exoplanets and Stellar Astrophysics at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, where she is the incoming senior project scientist for the Hubble Space Telescope. From 2003 to 2006, she served as the program scientist for the Hubble at NASA Headquarters in Washington, D.C. She received her bachelor’s degree in physics from MIT and her Ph.D. in Astronomy from Harvard University in 1995. Wiseman discovered periodic comet 114P/Wiseman-Skiff while working as an undergraduate research assistant in 1987.
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The Secrets of Star Birth
In all the centuries people have looked at the night sky, one thing has not changed. The universe is just bursting with stars. Anywhere we look, in any direction, we see millions and billions and trillions of stars.
But here’s a really surprising thing: Until very recently, nobody had ever seen a star actually forming. We see clouds of gas and dust. We see new stars inside clouds of gas and dust. But exactly how all that gas turns into stars in the first place has been mostly hidden. It’s as if children were dropped off on our doorsteps as newborns, and nobody had ever seen a live birth. But that’s starting to change.
[sound of keyboard tapping…]
“What I wanted to show you was…. If I can find it…”
That’s Jennifer Wiseman. She is an astrophysicist at NASA’s Goddard Space Flight Center. She knows a lot about star birth and she at her computer Googling for snapshots of baby stars taken by the Herschel Space Observatory. The images show protostars. Those are huge hot glowing spheres of gas that haven’t yet become fully-fledged stars. Protostars are kind of like the fetal stage of star formation.
If you look closely you’ll see these filaments everywhere, and along these filaments you see these chains of bright spots. There are protostars forming along the filament as it fragments into these chains of clumps and stars. It’s like beads on a string. So we now are getting the picture that that’s how stars form in these clouds—that the clouds fragment into these long strings, and then the strings form chains of stars.
I’ve come to Wiseman’s office to get a progress report on the science of star formation. Herschel has already provided stunning new looks at protostars. And a telescope under construction in a desert in Chile will reveal even finer details. These new astronomy tools will provide the equivalent of a fetal ultrasound scanner to see deep into the clouds of gas and dust where stars are born.
Star formation is a very exciting process. We didn’t really understand it until starting a few decades ago when we started to be able to see in wavelengths of light other than visible light.
As a new star forms it produces light at different wavelengths. Sort of like different colors in a rainbow. Visible light, meaning wavelengths the human eye can see, is absorbed by the gas and dust in the star’s birth cloud. But some kinds of light manage to leak out, like infrared light and radio waves. Telescopes that pick up these emissions can see deep into star forming clouds.
When we started using things like infrared telescopes and radio telescopes, we suddenly had a new window into this hidden process of stellar birth.
Wiseman was just one of the scientists who looked through that new window. She used radio telescopes. Atoms of gas around new stars are like little radio transmitters. If you tune into the right channel, you can map the interiors of star forming clouds. Wiseman mapped humungous jets of matter and energy that spew from the poles of young stars. In our Milky Way galaxy and others like it, star birth ignites within giant clouds scattered along the galaxy’s spiral arms. Here’s how it works.
We start out with a galactic disk. The spiral arms are full of these clouds of dense gas and dust. Most of the volume isn’t stars, it’s gas and dust. We have a lot of turbulence in the galaxy. The galaxy is rotating. We have things going off in the galaxy, like supernova explosions of old stars that inject shock fronts and turbulence. This can start cycles of motion within these interstellar clouds that can stir up little eddies of high density. That’s one of the triggering mechanisms for getting these larger clouds to start a process that’s called fragmentation.
Fragmentation just means that a really big cloud starts to break up into smaller chunks. That has to happen before stars can form. And if you look closely at a fragmenting cloud, you see long twisty filaments of gas and dust. Stars form in chains along the filaments.
There’s a lot of modeling about how clouds start shredding into long filaments. These filaments can fragment into whole chains of dense cores of gas. And it’s these chains of dense cores along these filaments that if they have enough density, enough mass, will collapse gravitationally and become stars or clusters of stars.
Images from the Herschel Space Observatory -– the ones she Googled up for me a while ago — show chains of cores along filaments of gas. Those are the beads on a string that Wiseman mentioned earlier. Within the beads, gravity will give birth to new stars, each starting out as a protostar.
Young protostars are buried in a large envelope of dense gas, kind of flattened like a fluffy pancake. And the interior part of this material is being gravitationally sucked into a much tighter accretion disk that’s right around this young forming star.
So when is a star born? Its birth cry is called nuclear fusion. That’s when gravity crushes hydrogen into heavier helium atoms. It’s what makes the sun shine, and it’s what makes a star a star.
But once that star accretes enough of the surrounding gas, it will begin the process of fusion in the core. Hydrogen will begin to turn into helium and release light, and that becomes a star.
Wiseman and many other scientists tell a pretty detailed story of how stars are born. But soon, powerful new tools will allow astronomers to probe star formation in much greater detail.
We have a new space telescope that’s called the Herschel Space Observatory. That’s a partnership between the European Space Agency and NASA working together. And we’re building a new array of radio telescopes that will be on the ground in South America. It’s called ALMA, for the Atacama large millimeter array, which is a radio telescope array that is sensitive to wavelengths that are in the range of millimeters. And that gives you a window into a certain type of hot gas around stars.
ALMA will pick up where Herschel leaves off. The new radio telescope be composed of up to 80 antennas spread out across a plain in the Chilean Andes. Those individual antennas will act as one collecting dish. That means ALMA will be able to tune into sharper details than Herschel can with its single mirror. By tuning into warm gas near the protostar, ALMA may give us our first look at the accretion zone.
So the combination of very sharp angular resolution and submillimeter wavelengths gives you a tool to see this accretion zone. So all this speculation that we’re doing about what it might be like in that inner accretion zone, we’ll be able to actually, finally map it.
And astronomers care very much about accretion zones. Why? Because that’s where planets come from. So understanding star formation may ultimately give us some new clues to how and why planets form in the first place.
End of podcast:
365 Days of Astronomy
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