The COSI gamma ray telescope, shown in this artist’s sketch, will map the Milky Way galaxy to find sources of gamma ray emission, which is expected to include remnants of supernova explosions, accreting black holes and the mergers of neutron stars. The background image is an artist’s impression of the material ejected during a supernova explosion. (Image by Jim Willis, courtesy of Northrop Grumman Corporation ½ Space Systems; background image courtesy of European Southern Observatory)

[by Bob Sanders, UCB Media Relations]

In an announcement last week, NASA selected the Compton Spectrometer and Imager (COSI) mission, which is led by UC Berkeley’s Space Sciences Laboratory (SSL), to advance toward a scheduled launch in 2025. The mission budget is estimated at $145 million, not including launch costs.

The telescope will map low energy, or “soft,” gamma ray emissions over the full sky during its two-year mission. Gamma rays are produced during the decay of unstable isotopes of atoms such as iron, aluminum and titanium, which are produced when massive stars explode. By mapping gamma ray emissions throughout the galaxy, COSI will be able to chart new and recent supernovae and help the understanding of how they manufacture and seed the galaxy with elements.

COSI “will revolutionize our understanding of the creation and destruction of matter in the galaxy and beyond,” said SSL research scientist John Tomsick, the mission’s principal investigator, in a video tweeted last week by Thomas Zurbuchen, associate administrator for the NASA’s Science Mission Directorate in Washington.

“For more than 60 years, NASA has provided opportunities for inventive, smaller-scale missions to fill knowledge gaps where we still seek answers,” Zurbuchen said, in announcing the award. “COSI will answer questions about the origin of the chemical elements in our own Milky Way galaxy, the very ingredients critical to the formation of Earth itself.”

One key objective of the mission is to understand why the Milky Way contains more positrons, which are the antimatter partners of electrons, than would be expected based on the known sources, primarily supernovae, in the galaxy. When positrons encounter electrons, the two annihilate one another and produce pairs of gamma rays of the same specific energy. Mapping this gamma ray wavelength will tell astronomers where the positrons are.

“There are more positrons out there than can be accounted for from supernovae alone, and the origin of the excess is unknown,” Tomsick said. “So, one thing we’re going to do is map in detail where the positrons are coming from to understand how they’re produced.”

Other possible sources of positrons include the supermassive black hole at the center of the galaxy, an unseen population of small black holes about the mass of our sun, or the annihilation of dark matter particles, which could theoretically produce positrons.

Read more in the full Berkeley News article.