(Photo: Kavli Institute for the Physics and Mathematics of the Universe)
A small satellite galaxy of the Milky Way called Sagittarius (lower left green orb) is seen from Earth through gamma-ray giant lobes (also known as Fermi bubbles, purple regions above and below the galaxy). Sagittarius is packed with dark matter, but this is unlikely to be the cause of the observed emissions.
An international team of astronomers has discovered a small satellite galaxy of the Milky Way laden with dark matter, the emission of which may be the result of a millisecond pulsar that uses a massive gamma-ray plume to eject cosmic particles. high.
Gamma rays solve cosmic anomalies
In case you didn’t know, the center of the Milky Way galaxy constantly emits a pair of giant gamma-ray bubbles spanning 50,000 light-years. It was discovered about ten years ago by the Fermi Gamma-ray Space Telescope. Phys.org reports that the origin of this hourglass-shaped anomaly remains unknown.
In detail, these radiation lobes, known as Fermi bubbles, are filled with some cryptic substructure of intense gamma-ray emissions. One of his brightest regions in the southern lobe, the Fermi cocoon, was assumed to have been caused by a previous explosion from the galaxy’s supermassive black hole.
But once an international team of researchers analyzed data from GAIA and the Fermi Space Telescope to discover that the Fermi cocoon came from an emission brought on by our next-door galaxy, the Sagittarius dwarf galaxy. This will change soon.
The study, called gamma-ray emission from the Sagittarius Dwarf Spherical Galaxy by millisecond pulsars, was led by former Kavli Institute of Physics and Mathematics (Kavli IPMU) project researcher Oskar Macias (now a GRAPPA Fellow at the University of Amsterdam) and Roland Crocker at the Australian National University. Shunsaku Horiuchi and Shinichiro Ando, Associate Professors and Kavli IPMU Visiting Fellows.
This Milky Way satellite galaxy can be glimpsed from Earth through a Fermi bubble. It has used up most of the interstellar gas because it orbited near our galaxy and passed through the galactic plane in the past. Many of its stars are torn from its center and stretch into streams. Given that Sagittarius was in a dormant state with no gas or stellar nurseries, the gamma ray emission could have come from either of her two sources. The first is due to an undiscovered mass of millisecond pulsars or dark matter annihilation.
For a little background, millisecond pulsars are remnants of a particular type of star that is much more massive than the Sun and is in a tight binary system. But now, due to its tremendous rotational energy, it emits cosmic particles. The millisecond pulsar’s electrons collide with low-energy photons from the cosmic microwave background, accelerating them into high-energy gamma rays.
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The researchers established that the gamma-ray cocoon could be explained by the Sagittarius dwarf’s millisecond pulsar, ruling out dark matter. Their findings provide insight into millisecond pulsars as excellent accelerators for extremely powerful electrons and positrons. We also show that similar physical processes may occur in other dwarf galaxies in the Milky Way.
“Our work forces a reassessment of the high-energy emitting capabilities of stationary stars, such as dwarf spherical galaxies, and their role as prime targets in the search for dark matter annihilation,” Macias said.
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