In February 1987, light from an exploding star arrived at Earth after
traveling across 160,000 light-years of space. It was the closest
supernova humanity had seen in centuries. Thirty-two years later, the
light of the supernova itself has faded, but astronomers continue to
study its remains for clues about how stars live and die. Scientists
will use NASA's James Webb Space Telescope to observe Supernova 1987A
(SN 1987A), as it is known, in order to gain new insights into the
physics of the explosion and its aftermath.
When you look at a photo of SN 1987A, two features stand out: a
clumpy outer ring that looks like a pearl necklace, and an inner blob.
The outer ring is material that the star shed thousands of years ago.
When the supernova's blast wave hit this ring, it caused the previously
invisible material to heat up and glow. The inner blob is material
ejected when the star exploded.
That ejected material revealed a surprise when astronomers observed
it with the European Space Agency’s infrared Herschel Space Observatory.
They found that it contained an entire sun's worth of cold dust. More
recently, NASA’s SOFIA (Stratospheric Observatory for Infrared
Astronomy) mission studied the ring and detected 10 times more dust than expected, indicating a growing amount of dust there, too.
Theories suggest that any dust within the ring that predated the
explosion should have been destroyed by the blast wave, and the ejecta
itself should be too hot for new dust to form. As a result, there should
be little dust within SN 1987A. Yet observations tell a different
story.
"Something has produced dust there. We need Webb to answer questions
like, how was the dust produced, and what is it made of?" said lead
researcher Margaret Meixner of the Space Telescope Science Institute and
Johns Hopkins University, both in Baltimore, Maryland.
What is dust, and why is it important?
Credits: NASA, ESA, and L. Hustak (STScI). Youtube
Cosmic dust is different from the dust bunnies that you find under
your furniture. It's smaller, mainly consisting of micron-sized
particles like those in smoke. And rather than being made of bits of
hair or clothing fibers, cosmic dust is composed of a variety of
chemical elements like carbon, silicon and iron all stuck together. As a
result, measuring the composition of a particular patch of cosmic dust
is challenging because the signatures of the elements blend together.
"We have no clue what the dust in Supernova 1987A is made of –
whether it's rocky and silicate-rich, or sooty and carbon-rich. Webb
will let us lcoearn not only the composition of the dust, but its
temperature and density," explained Olivia Jones of the United Kingdom
Astronomy Technology Centre, a co-investigator on the project.
As dust from dying stars spreads through space, it carries essential
elements to help seed the next generation of star and planet formation.
"Dust is what the planets are made out of, what we're made out of.
Without dust, you have no planets," said Jones.
Dust also is important for the evolution of galaxies. Observations
have shown that distant, young galaxies had lots of dust. Those galaxies
weren't old enough for sun-like stars to create so much dust, since
sun-like stars last for billions of years. Only more massive,
short-lived stars could have died soon enough and in large enough
numbers to create the vast quantities of dust astronomers see in the
early universe.
The birth of a supernova remnant
The team plans to examine SN 1987A with two of Webb's instruments: the
Mid-Infrared Imager (MIRI) and the Near-Infrared Spectrograph (NIRSpec).
With imaging, Webb will reveal features of SN 1987A far beyond any
previous infrared observations due to its exquisite resolution.
Astronomers expect to be able to map the temperature of the dust within
both the supernova ejecta and the surrounding ring. They can also study
the interaction of the blast wave with the ring in great detail.
This illustration demonstrates how a massive star
(at least 8 times bigger than our sun) fuses heavier and heavier
elements until exploding as a supernova and spreading those elements
throughout space. Credits: NASA, ESA, and L. Hustak (STScI). Hi-res image
Webb's true power will come from its spectroscopic measurements. By
spreading light out into a rainbow spectrum of colors, scientists can
determine not only chemical compositions but also temperatures,
densities, and speeds. They can examine the physics of the blast wave,
and determine how it is affecting the surrounding environment. They can
also watch the evolution of the ejected material and ring over time.
"We're witnessing the birth of a supernova remnant," said Patrice
Bouchet of DRF/Irfu/Astrophysics Department, CEA-Saclay in France, a
co-principal investigator for the MIRI European Consortium. "This is a
once-in-a-lifetime event."
"Supernova 1987A is an object that continually surprises people,"
said Meixner. "This is one you'll want to keep your eyes open for!"
The observations described here will be taken as part of Webb's Guaranteed Time Observation
(GTO) program. The GTO program provides dedicated time to the
scientists who have worked with NASA to craft the science and instrument
capabilities of Webb throughout its development.
The James Webb Space Telescope will be the world's premier space
science observatory when it launches in 2021. Webb will solve mysteries
of our solar system, look beyond to distant worlds around other stars,
and probe the mysterious structures and origins of our universe and our
place in it. Webb is an international project led by NASA with its
partners, the European Space Agency (ESA) and the Canadian Space Agency.
For more information about Webb, visit www.nasa.gov/webb.
By Christine Pulliam
Space Telescope Science Institute, Baltimore, Md.
Editor: Lynn Jenner
Source: NASA/Solar System and Beyond
