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Star (X-ray) Light, Star (X-ray) Bright
NASA: We have booster ignition and liftoff of Columbia, reaching new heights for women
and X-ray Astronomy.
Martin Elvis: The main thing Chandra does is take these superb, sharp images.
Narrator: Remember the line from the children's saying that goes: "Starlight, star bright,
first star I see tonight"? Looking at the light from stars is exactly how astronomers
can learn about them. But, stars do not just off so-called visible light, the type we can
see with the human eye. Rather, astronomers need to study stars in many different types
of radiation to get a complete picture of what is really happening of them.
Dr. Nancy Brickhouse studies stars with the Chandra X-ray Observatory and other telescopes
and instruments. She explains some of the basics of what stars are.
Nancy: A star is a ball of hot gas and in the center it's very, very dense and in the
center a star is producing nuclear fusion reactions, and that's basically what makes
the star hot. As you go out into the atmosphere of the star, eventually you reach what we
call the photosphere which is the surface of the star. The visible light color of the
star is actually coming from the photosphere.
Narrator: But, even though that might sound straightforward, there's really nothing simple
about stars. To begin with, there are many different kinds of stars: huge red stars called
red giants, small hot white stars called white dwarfs, small cool brown stars called brown
dwarfs, and more. Dr. Brickhouse explains how astronomers can keep track and X-rays
are used to help categorize these very different objects.
Nancy: Stars have a temperature that's related to the color of the star so the blue stars
are hotter than the yellow and red stars, and so we have a classification scheme that's
going from hot to cool and the sun is considered to be a cool star. And this is based on their
visible light properties. The color is basically related to the color of the photosphere. When
we look at these stars in X-rays we're looking above that surface, so we're looking higher
up in the atmosphere of the star, where the gas is really not as dense, but it's much
hotter. And it turns out that both hot stars and cool stars make X-rays but the processes
are different. So when we look at cool stars we're looking at processes that are more like
the Sun.
Narrator: But where does our Sun fit into the scheme of things? What does Chandra and
its X-ray data tell us about our nearest star?
Nancy: We can look at the Sun with other satellites and there have been X-ray missions for just
studying the sun, but it would wipe out Chandra's detectors if we used Chandra to look at the
Sun, but we can study other stars and it turns out that 10 to a hundred thousand times more
energy is produced in X-rays than what the sun produces, so by the standards of other
stars, the Sun is kind of a wimpy X-ray producer.
Narrator: So, astronomers can't use Chandra to study our Sun directly. But, what kind
of insight do astronomers actually get by studying other Sun-like stars using Chandra.
It turns out to be a very valuable thing to do.
Nancy: One of the reasons to look at other stars is to get some understanding of what
the processes are that cause the X-ray emission and what kind of diversity there might be
because it will help our models if we just have one system to look at even though we
can look at it in a lot of detail we don't necessarily understand the possibilities that
would help us constrain our models.
Narrator: Studying all kinds of stars - including those like our Sun and those that are very
different - remains an important area of research in astronomy and astrophysics. The starlight
we wish upon in that rhyme turns out to be much more complicated and informative than
we may have ever expected. Researchers using Chandra are helping to address some of questions
whose answers may only be found in their X-ray light.