Scientists hope to observe universe's first stars with JWST

Special technique will use foreground galaxy clusters to magnify these stars' light by a factor of 10,000.
By Laurel Kornfeld | Sep 14, 2018
Led by scientists at Arizona State University (ASU), an international team of astronomers is hoping to observe the universe's first stars with NASA's James Webb Space Telescope (JWST), now scheduled for launch in 2020.

JWST will be placed in interplanetary space 930,000 miles (1.5 million km) from Earth. Its large light collecting surface and infrared detectors make it ideal for observing the universe's earliest stars, which began forming between 200 million and 400 million years after the Big Bang.

These stars were initially very hot and radiated light in far ultraviolet wavelengths. However, due to the expansion of the universe, their light has now been shifted to longer infrared wavelengths, making them ideal targets for JWST's infrared detectors.

Researchers plan to use the technique of gravitational lensing to magnify the light from a foreground galaxy cluster to focus on and magnify the light of these early stars.

Instead of the usual 10-20-time magnification produced by gravitational lensing, the scientists will need to use a special technique that magnifies the stars' light by a factor of 10,000.

Known as a "caustic transit," this technique involves using a special alignment of the ancient stars with foreground galaxy clusters over several weeks, during which time the cluster moves across the sky between Earth and the stars.

Because the galaxies in the cluster are spread out, they create multiple magnified images that trace a pattern in space.

"Depending on which side of the caustic it approaches from, a first star would brighten over hours--or several months. Then after reaching a peak brightness for several weeks, it would fade out again, either slowly or quickly, as it moves away from the caustic line," explained Rogier Windhorst of ASU's School of Earth and Space Exploration.

The early universe contained only hydrogen and helium, so the earliest stars are composed solely of these elements and have easily identifiable spectra.

Heavier elements, such as carbon, oxygen, and iron, formed later when these stars exploded as supernovae.

By observing the universe's earliest stars, scientists will be able to determine the properties of the early universe, which up to now could be done only via computer simulations.

"We want to answer questions about the early universe, such as, were binary stars common, or were most stars single? How many heavy chemical elements were produced, cooked up by the first stars, and how did those first stars actually form," said Frank Timmes, also of ASU's School of Earth and Space Exploration.

A paper discussing potential observation methods for this project has been published in the Astrophysical Journal Supplement.

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