Universe ID: 13209

NASA’s Fermi Finds Vast ‘Halo’ Around Nearby Pulsar

Released on December 19, 2019

A new study of observations from NASA’s Fermi Gamma-ray Space Telescope has discovered a faint but sprawling glow around a nearby pulsar. If visible to the human eye, this gamma-ray “halo” would appear larger in the sky than the famed Big Dipper star pattern. This structure may provide the solution to a long-standing mystery about the amount of antimatter in our neighborhood.

Astronomers have been vexed by a decade-long puzzle about one type of cosmic particle arriving from beyond the solar system. Positrons, the antimatter version of electrons, turn out to unusually abundant near Earth.

A neutron star is the crushed core left behind when a star much more massive than the Sun runs out of fuel, collapses under its own weight and explodes as a supernova. We see some neutron stars as pulsars, rapidly spinning objects emitting beams of radio waves, light, X-rays and gamma rays that, much like a lighthouse, regularly sweep across our line of sight.

Geminga (pronounced geh-MING-ga) is among the brightest pulsars at gamma-ray energies.
To study its halo, scientists had to subtract out all other sources of gamma rays, including diffuse light produced by cosmic ray collisions with interstellar gas clouds. Ten different models of interstellar emission were evaluated.

What remained when these sources were removed was a vast, oblong glow spanning some 20 degrees — about 40 times the apparent size of a full Moon — at an energy of 10 billion electron volts (GeV), and even larger at lower energies.

The team determined that Geminga alone could be responsible for as much as 20% of the high-energy positrons seen by other space experiments. Extrapolating this to the cumulative emission of positrons from all pulsars in our galaxy, the scientists say it’s clear that pulsars remain the best explanation for the observed excess of positrons.

This model of Geminga's gamma-ray halo shows how the emission changes at different energies, a result of two effects. The first is the pulsar's rapid motion through space over the decade Fermi's Large Area Telescope has observed it. Second, lower-energy particles travel much farther from the pulsar before they interact with starlight and boost it to gamma-ray energies. This is why the gamma-ray emission covers a larger area at lower energies. One GeV represents 1 billion electron volts — billions of times the energy of visible light.

Credit: NASA’s Goddard Space Flight Center/M. Di Mauro

GIF version

This animation shows a region of the sky centered on the pulsar Geminga. The first image shows the total number of gamma rays detected by Fermi’s Large Area Telescope at energies from 8 to 1,000 billion electron volts (GeV) — billions of times the energy of visible light — over the past decade. By removing all bright sources, astronomers discovered the pulsar’s faint, extended gamma-ray halo.

Credit: NASA/DOE/Fermi LAT Collaboration

This video opens on a region of the sky centered on the pulsar Geminga. The image shows the total number of gamma rays detected by Fermi’s Large Area Telescope at energies from 8 to 1,000 billion electron volts (GeV) — billions of times the energy of visible light — over the past decade. By removing all bright sources, astronomers discovered the pulsar’s faint, extended gamma-ray halo.

Credit: NASA/DOE/Fermi LAT Collaboration

Starlight interacting with particles travelling close the speed of light can be boosted to gamma-ray energies. This animation shows the process, known as inverse Compton scattering. Light ranging from microwave to ultraviolet wavelengths collides with a fast-moving particle and transforms into a gamma ray, the highest-energy form of light.

Credit: NASA’s Goddard Space Flight Center

These images show a region of the sky centered on the pulsar Geminga. Left: The total number of gamma rays detected by Fermi’s Large Area Telescope at energies from 8 to 1,000 billion electron volts (GeV) — billions of times the energy of visible light — over the past decade. Brighter colors correspond to greater numbers of gamma rays. Right: By removing all bright sources, astronomers discovered the pulsar’s faint, extended gamma-ray halo.

Credit: NASA/DOE/Fermi LAT Collaboration

For More Information

https://www.nasa.gov/feature/goddard/2019/nasa-s-fermi-mission-links-nearby-pulsar-s-gamma-ray-halo-to-antimatter-puzzle

Credits

Francis Reddy (University of Maryland College Park): Lead Science Writer
Scott Wiessinger (USRA): Lead Producer
Mattia Di Mauro (Catholic University of America): Lead Scientist

Please give credit for this item to:
NASA's Goddard Space Flight Center. However, individual items should be credited as indicated above.

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Mission:
Fermi Gamma-ray Space Telescope

Data Used:

Fermi

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Keywords:
SVS >> Antimatter
SVS >> Neutron Star
SVS >> Positron
SVS >> Astrophysics
SVS >> Pulsar
SVS >> Space
SVS >> Fermi
NASA Science >> Universe
SVS >> Gamma Ray