NASA Selects Gamma-Ray Mission to Explore Positron Sources, Supernovae

COSI spacecraft in front of image of supernova 1987A
An artist’s idea reveals NASA’s COSI gamma-ray mission in entrance of Supernova 1987A.
University of Berkeley / COSI

NASA introduced this week that it has selected the Compton Spectrometer and Imager (COSI) gamma-ray telescope, led by John Tomsick (University of California, Berkeley), for improvement as a part of its Small Explorer (SMEX) program. The mission will price roughly $145 million, excluding launch provider.

With an anticipated launch date in 2025, COSI will examine the current historical past of star beginning, star loss of life, and the formation of chemical parts within the Milky Way. To accomplish this, the observatory will take a look at galactic sources producing gamma-ray energies between 0.2 and 5 million electron-volts (0.2–5 MeV).

COSI would be the first gamma-ray telescope mission designed to catch the annihilation of positrons, the anti-matter model of electrons. What’s extra, the telescope could have the decision to pinpoint the place these particles come from. Since the 1970s, astronomers have seen gamma-ray emission attributed to positrons coming from the galactic heart area, however their supply(s) are nonetheless mysterious.

The mission may also probe the formation and decay of heavier parts revealed in cataclysmic supernovae. In addition, the observatory will pinpoint gamma-ray counterparts to unique sources throughout the sky, together with supernovae, blazars, and merging neutron stars producing gravitational waves.

“COSI will fly after the next upgrade to the gravitational wave detectors, so we are expecting to see larger numbers of events where gravitational waves and gamma-rays are detected,” says Tomsick.

Designing the Detector

Gamma rays are high-energy photons which can be troublesome to detect and focus, however they make clear a number of the most energetic processes within the universe. COSI’s design provides enhancements in spectral and angular decision, all-sky protection, and elevated sensitivity at gamma-ray wavelengths versus earlier observatories.

Because Earth’s ambiance absorbs gamma-rays, gamma-ray astronomy should be finished from both high-altitude balloons or space. So as a part of the mission’s improvement, the workforce constructed a balloon-borne model of COSI as a proof of idea. The workforce launched the telescope payload aboard NASA’s Superpressure Balloon from the Wanaka, New Zealand web site in May 2016. (It was aloft almost 47 days, a record for a mid-altitude, giant scientific analysis balloon.)

COSI Balloon
The COSI balloon mission prior to launch.
University of Berkeley / COSI
The COSI payload prior to restoration in Antarctica.
University of Berkeley/COSI/Scott Battion

“COSI is a Compton telescope, a type of telescope that observes what’s known as Compton scattering, and its operation is very different from an optical or even an X-ray telescope,” says Tomsick.

Compton scattering will get its identify from gamma-ray researcher and pioneer Arthur Compton, who realized that when a gamma-ray photon interacts with a charged particle like an electron, the photon offers up a few of its vitality to the electron. By monitoring the scatter sample of a gamma ray within the detector, researchers can determine the place it got here from, roughly talking.

“The Compton scattering angle defines a circle on the sky,” explains Tomsick. “Once you have hundreds or thousands of gamma-rays, the sources [they’re coming from] show up in the sky because the circles overlap at the locations of the sources.”

Compton circles
This animation reveals a simulated view of a 0.662 MeV gamma-ray supply as detected by COSI. Each particular person gamma-ray coming into the detector generates its personal “Compton circle.” Some particular person circles are fairly giant, however because the detector collects extra gamma-ray occasions, it will definitely properties in on the place the supply is on the sky.
University of California, Berkeley / COSI

The identify Compton crops up usually in high-energy astrophysics. COSI shares it with the Compton Gamma-Ray observatory, which operated at 0.02 MeV to 30 GeV and was in Earth orbit from 1991 to 2000. The observatory had an instrument named COMPTEL that acted equally to COSI, however COSI will characteristic a subject of view 4 instances bigger, with angular decision twice as sharp and vitality decision 20 instances higher. COSI may also cowl the essential 511 keV electron-positron annihilation line.

Currently, NASA has two different orbiting gamma-ray observatories in operation, the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope.

This week’s choice comes as one other SMEX mission is readied for launch: the Imaging X-Ray Polarimetry Explorer (IXPE), due to carry off from the Cape on December ninth atop a SpaceX Falcon 9 rocket.

COSI was one in all 4 mission ideas within the operating for the final spherical of picks. Two others have been the Large Area burst Polarimeter (LEAP) and the Gravitational-wave Ultraviolet Imager, each of which might have been mounted aboard the International Space Station. The last runner-up was the Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission.

SMEX alumni embrace missions such because the Interstellar Boundary Explorer (IBEX) and the Nuclear Spectroscopic Telescope Array (NuSTAR).

It might be thrilling to see what COSI reveals concerning the gamma-ray universe.

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