Science & Technology

NASA uses Fermi Telescope to trace the history of star-formation

Location of 739 blazars used in the Fermi Gamma-ray Space Telescope’s measurement of the extragalactic background light (EBL) (NASA/Goddard/Fermi)
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Researchers at NASA have used data from the Fermi telescope to measure starlight produced over 90% of the Universe’s history and confirm theories regarding the boom-period of star-formation, research published in the latest edition of Science has revealed.

The research focused on Gamma-ray output from distant galaxies to estimate stellar formation rates through the history of the Universe and lay down a template for future examinations of early stellar-development.

The new study hasn’t just independently confirmed previously obtained results, but built upon the findings by removing biases and shortfalls from those studies.

Lead scientist Marco Ajello, an astrophysicist at Clemson University in South Carolina said: “Stars create most of the light we see and synthesize most of the universe’s heavy elements, like silicon and iron.

“Understanding how the cosmos we live in came to be, depends in large part on understanding how stars evolved.”


Artist’s impression of the Fermi space-telescope in orbit around Earth (NASA)

Artist’s impression of the Fermi space telescope in orbit around Earth (NASA)

The primary mission of the Fermi-telescope, launched into orbit 10-years-ago, has been to observe the ‘ cosmic fog’ of all the ultraviolet, visible and infrared light produced by stars over the Universe’s history collectively known as extragalactic light (EBL). This light will long outlast its source continuing to travel across the cosmos, thus measuring the EBL allows astronomers to study the stellar-formation and evolution of long-dead stars.

David Thompson, Fermi’s deputy project scientist describes the recent findings: “This is an independent confirmation of previous measurements of star-formation rates.

“In astronomy, when two completely independent methods give the same answer, that usually means we’re doing something right. In this case, we’re measuring star formation without looking at stars at all but by observing gamma rays that have traveled across the cosmos.”

Gamma rays are the highest frequency and thus the most energetic form of electromagnetic radiation when they interact with interact with other frequencies of light, matter can be created via Einsteins famous energy-mass equivalence, E=mc². An example of this is the creation of electrons and positrons when high-energy gamma-rays interact with infrared light and when lower-energy gamma-rays interact with higher energy light.

Fermi’s ability to detect gamma-rays makes it extremely well-suited for mapping the EBL spectrum. The above-listed interactions are common enough over cosmic distances that the further back cosmologists look, the more evident their effects on gamma-ray sources are, allowing a deep-examination of the Universe’s stellar population.

The researchers led by Vaidehi Paliya examined gamma-ray signals from almost 750 galaxies with supermassive black holes at their center known as blazars collected over a nine-year period by Fermi’s Large Area Telescope (LAT) to estimate how the EBL has built over time.

The study has confirmed previous results that show the peak-period of star-production was 10 -billion years ago. The improvement this new research has made on these studies comes from the fact that previous star-surveys have often missed fainter stars and galaxies. This means that they couldn’t account for star formation in intergalactic space.

This population has previously only been estimated, whereas the EBL includes contributions starlight from these sources, thus providing a more complete picture of star formation. The method has been used before, but the number of blazars surveyed was a fraction of those observed in this new study.


It is expected that the outcome of this study will help guide the future work of the James Webb Telescope (NASA)

It is expected that the outcome of this study will help guide the future work of the James Webb Telescope (NASA)

It is expected that the outcome of this study will help guide the future work of the James Webb Telescope (JWST) expected to launch in 2021.

Co-author Kári Helgason, an astrophysicist at the University of Iceland, said: “One of Webb’s primary objectives is to unravel what happened in the first billion years after the big bang.

“Our work places important new limits on the amount of starlight we can expect to see in those first billion years — a largely unexplored epoch in the universe — and provides a benchmark for future studies.”

Original research:

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