[2 of 2]    Researchers use gamma rays to detect tiny nearby galaxies filled with dark matter

    Figure 1. A small satellite galaxy of the Milky Way called Sagittarius (lower left green orb) is seen from Earth through a giant lobe of gamma rays (also known as the Fermi bubble, 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. Credit: Kavli IPMU

    Through a giant lobe of gamma rays, an international team of researchers discovered a small satellite galaxy of the Milky Way filled with dark matter, an emission that could be the result of a millisecond pulsar that blew away cosmic particles. high, new research reports natural astronomy.

    The center of our Galaxy is blowing out a pair of giant gamma-ray bubbles (magenta structures in Figure 1) that span 50,000 light-years. The cause of this hourglass-shaped phenomenon, which was discovered by Fermi’s Gamma Ray Space Telescope about a decade ago, remains unknown.

    These radiation lobes, called Fermi bubbles, are patched with several cryptic substructures of very bright gamma-ray emissions. One of the brightest spots, called the Fermi cocoon, is in the southern lobe (enlarged inset of Fig. 2) and was originally thought to be a past explosion from the galaxy’s supermassive black hole.

    An international research team led by former Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Specially Appointed Researcher Oskar Macias (currently a GRAPPA Fellow at the University of Amsterdam) and Associate Professor Roland Crocker of the Australian National University. IPMU Visiting Scientists Shunsaku Horiuchi and Shinichiro Ando analyzed data from GAIA and the Fermi Space Telescope and revealed that the Fermi cocoon is actually an ejection from the Sagittarius dwarf galaxy.

    This satellite galaxy of the Milky Way is seen through the Fermi bubble from our position on Earth (Fig. 1). Due to the tight orbit around our galaxy and the previous passage through the galactic disk, it has lost most of its interstellar gas and many of its stars have been torn from their cores into elongated streams.

    Given that Sagittarius is stationary and has no gas or stellar nurseries, its gamma-ray emission probabilities are small, including i) an unknown mass of millisecond pulsars, or ii) the annihilation of dark matter. There was only one possibility.

    [2 of 2]    Researchers use gamma rays to detect tiny nearby galaxies filled with dark matter

    Figure 2. Gamma-ray image of the Fermi bubble (blue) overlaid on a map of the RR Lyrae star (red) observed with the GAIA telescope. The shape and orientation of the Sagittarius (Sgr) dwarf are perfectly consistent with those of the Fermi cocoon, a gamma-emitting bright substructure in the southern part of the Fermi bubble. This is strong evidence that the Fermi cocoon is due to an energetic process occurring in Sagittarius, which is located behind the Fermi bubble. Credit: Crocker, Macias, Mackey, Krumholz, Ando, ​​Horiuchi et al. (2022)

    Millisecond pulsars are the remnants of a particular type of star, much more massive than the Sun, close to binary star systems, and exploding cosmic particles as a result of extreme rotational energy. Electrons emitted by millisecond pulsars collide with low-energy photons of the cosmic microwave background, emitting high-energy gamma rays.

    The researchers didn’t like the dark matter explanation, having demonstrated that the gamma-ray cocoon could be explained by a millisecond pulsar in a Sagittarius dwarf.

    Their findings shine a light on millisecond pulsars as efficient accelerators of high-energy electrons and positrons, and also suggest that similar physical processes may be underway in other dwarf satellite galaxies of the Milky Way. .

    “This is important because dark matter researchers have long believed that observations of gamma rays from dwarf satellites provide definitive evidence of dark matter annihilation. “We are forcing a reassessment of the high-energy emission capabilities of dwarf spherical galaxies and their role as prime targets in the search for dark matter annihilation,” Macias said.

    Details of their research are natural astronomy September 5th.

    Gamma rays from dwarf galaxies solve astronomical puzzles

    For more information:
    Roland M. Crocker et al., Gamma-ray emission from the Sagittarius dwarf spherical galaxy by a millisecond pulsar, natural astronomy (2022). DOI: 10.1038/s41550-022-01777-x

    Courtesy of the Kavli Foundation

    Quote: The researchers obtained a small neighboring galaxy (September 11, 2022 ) to discover the source of gamma rays

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