The Science behind the Stars ctY Astrophysics by Spencer McClung

The Science
behind the Stars
CTY Astrophysics
by Spencer McClung
The planetary nebula designated NGC 2818, which lies in the
southern constellation of Pyxis (the Compass), was imaged
by the Hubble Space Telescope in 2009. The spectacular
structure of the nebula contains the outer layers of a star that
were expelled into interstellar space. The glowing gaseous
shrouds in the nebula were shed by the central star after it ran
out of fuel to sustain the nuclear reactions in its core.
10 imagine
Sept/Oct 2014
NASA, ESA, Hubble Heritage Team (STScI/AURA).
w
O
n day three of CTY Astrophysics, we were given a series
of images of light from a star and had to determine the
mass of its binary companion. For an hour we used two sticks
to monitor small changes in the star’s light and then used a
very long series of calculations with very big numbers. In the
end, we were off by a couple orders of magnitude, but this
hands-on exploration of scale and distance gave us a taste
of some of the challenges astronomers have been tackling
for centuries.
After this introduction to spectral analysis, we went on to
examine photos of stars taken over a period of six months by
the Hubble Space Telescope. We were looking specifically for
changes in light of another star: If a star’s brightness decreased,
we learned, there was most likely a planet transiting the star
and blocking its light. From the amount of light lost, it is possible to determine the approximate size and composition of
the planet passing in front of the star. At first glance, the pictures we were analyzing looked the same; but, using computers to calculate differences in light, we found that a planet was
orbiting the star. Obviously we couldn’t see the planet, but it
was thrilling to learn from the data that it was there.
In addition to learning how to calculate the size of celestial
objects, we discussed the life cycle of stars, from gaseous nebulas to rapidly spinning neutron stars. The process of stellar
evolution that I found most interesting was nuclear fusion,
which is essential to the chemical makeup of the universe.
To put things simply, four hydrogen atoms under extremely
immense pressure and temperature join to form a helium
atom. Some of the mass of the hydrogen atoms is released as
energy (as Mr. Einstein’s e=mc2 explains) when they form the
lighter helium atom. This process repeats itself in the center
of stars with three helium atoms combining to form a carbon
atom. For the most massive stars, this continues until finally
iron is formed. Then the weight is so great that the star collapses in on itself and explodes in a supernova, which is how
almost every atom heavier than iron is created. That means
that any gold or silver you may be wearing was created in the
center of a supermassive explosion billions of times brighter
than our Sun. Intense, right?
Astrophysics is all about extremes. We dealt with numbers
as high as 1030 when calculating masses of supernovas and
as low as 10-30 when calculating atomic masses and energies.
By figuring out how much energy is released in a single reaction, you can determine the entire energy output of a star.
Using these massive numbers, we realized how precise scientists must be. For the moon landing, for example, an extra
pound of force could have been catastrophic—yet we were
getting answers that were off by multiple orders of magnitude. Although this was acceptable in class (considering the
processing power of student calculators versus supercomputers), the class constantly strove for improvements, getting
more exact answers every day. It became almost a game to see
who could calculate most precisely how many atoms are in
our Sun.
While I had expected this course to involve calculations
and math, I was surprised to delve into topics I had no
idea really existed, such as flux. To my class’s dismay, we
learned that flux is not the essential part of a time-traveling
DeLorean, but the radiation output of a star. We talked
about a huge range of topics related to space, from black
holes to neutron degeneracy to time travel to Carl Sagan. I
learned how to draw conclusions from different data: Just
as professional astrophysicists learned everything we know
about black holes from the change in stars nearby, we used
data to recognize exoplanets and the chemistry of super-
To my class’s dismay, we
learned that flux is not
the essential part of a
time-traveling Delorean,
but the radiation output
of a star.
novas. The course gave me a better understanding of our
universe and how it works.
After taking this course, I started visiting the Astronomy
Picture of the Day website, which features a new photograph
of astronomy content with a description detailing the science
behind it. I’ve always appreciated images of stars, planets,
and galaxies. Now, after three weeks of studying, analyzing,
observing, measuring, and investigating celestial objects, I’ve
come to see these images as not just beautiful pictures, but as
representations of beautiful science. n
Spencer McClung is a junior at Glenelg
Country School in Ellicott City, MD. He runs
on the varsity cross country team, runs and
throws discus on the varsity track team, and
is a member of the robotics team. Spencer
is active in scouting and recently went to
Philmont Scout Ranch. He was a “nevermore” at CTY Lancaster
this summer, where he took Number Theory.
imagine
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