Tracing the History of Starlight with NASA’s Fermi Mission


Video Transcript

[Music] Scientists have now traced all the starlight across ninety percent of cosmic history, thanks to NASA’s Fermi Gamma-ray Space Telescope. Fermi studies the universe using gamma rays, the highest-energy form of light. Over the last 10 years, Fermi has measured gamma rays from nearly 2,000 blazars. These galaxies host supermassive black holes and produce jets of high-speed particles. Gamma rays from these blazars interact with starlight produced throughout the cosmos. Even after stars burn out, their light continues to travel across the universe, forming the extragalactic background light, or EBL. When a gamma ray collides with starlight, it transforms into two particles, an electron and a positron, in accordance with Einstein’s famous equation. These collisions weaken a blazar’s gamma-ray signal like fog dulling a car’s headlights. The further back scientists look, the greater the EBL’s dimming effect. A new study of the EBL peered back through 12 billion years of starlight, confirming that star formation in our universe peaked about 10 billion years ago. Stars create most of the light in the universe and many of its heavy elements, like silicon and iron. Understanding how our cosmos came to be depends in large part on understanding how stars evolved. Thanks to Fermi, we’re one step closer. [Music] [Music] [Music][Beeping] [Beeping] [Beeping]

Video Description

Scientists using data from NASA’s Fermi Gamma-ray Space Telescope have measured all the starlight produced over 90 percent of the universe’s history. The analysis, which examines the gamma-ray output of distant galaxies, estimates the formation rate of stars and provides a reference for future missions that will explore the still-murky early days of stellar evolution.

One of the main goals of the Fermi mission is to assess the extragalactic background light (EBL), a cosmic fog composed of all the ultraviolet, visible and infrared light stars have created over the universe’s history. Because starlight continues to travel across the cosmos long after its sources have burned out, measuring the EBL allows astronomers to study stellar formation and evolution separately from the stars themselves.

The collision between a high-energy gamma ray and infrared light transforms the energy into a pair of particles, an electron and its antimatter counterpart, a positron. The same process occurs when medium-energy gamma rays interact with visible light, and low-energy gamma rays interact with ultraviolet light. Enough of these interactions occur over cosmic distances that the farther back scientists look, the more evident their effects become on gamma-ray sources, enabling a deep probe of the universe’s stellar content.

The scientists examined gamma-ray signals from 739 blazars — galaxies with monster black holes at their centers — collected over nine years by Fermi’s Large Area Telescope (LAT). The measurement quintuples the number of blazars used in an earlier Fermi EBL analysis published in 2012 and includes new calculations of how the EBL builds over time, revealing the peak of star formation around 10 billion years ago.

Music: “Inducing Waves” from Killer Tracks

Credit: NASA’s Goddard Space Flight Center
Scott Wiessinger (USRA): Lead Producer
Jeanette Kazmierczak (University of Maryland College Park): Lead Science Writer
LK Ward (USRA): Narrator
Francis Reddy (University of Maryland College Park): Science Writer

Read more:

This video is public domain and may be downloaded at:

If you liked this video, subscribe to the NASA Goddard YouTube channel:

Follow NASA’s Goddard Space Flight Center
· Instagram
· Twitter
· Twitter
· Facebook:
· Flickr

Author: dhobson