A small satellite galaxy (green world on the bottom left) of the Milky Way– called Sagittarius– has actually been observed from Earth through huge lobes of gamma radiation (aka the Fermi bubbles, purple locations below and above the galaxy). Sagittarius is packed with dark matter, this is unlikely to be the cause of the observed emission. Gamma-ray image of the Fermi bubbles (blue) overlaid on a map of RR Lyrae stars (red) observed by the GAIA telescope. The shape and orientation of the Sagittarius (Sgr) dwarf match completely well those of the Fermi cocoon– an intense substructure of gamma-ray radiation in the southern part of the Fermi bubbles. This is strong proof that the Fermi cocoon is due to energetic procedures taking place in Sagittarius, which from our viewpoint, is located behind the Fermi bubbles.
A little satellite galaxy (green world on the bottom left) of the Milky Way– called Sagittarius– has actually been observed from Earth through giant lobes of gamma radiation (aka the Fermi bubbles, purple areas listed below and above the galaxy). Sagittarius is stuffed with dark matter, this is not likely to be the cause of the observed emission. Credit: Kavli IPMU
Researchers have actually used gamma rays to identify a small surrounding galaxy..
According to a new research study just recently released in the journal Nature Astronomy, a worldwide group of researchers has discovered a small satellite galaxy of the Milky Way filled with dark matter, but its emissions are more most likely the consequence of millisecond pulsars shooting out cosmic particles.
The center of our galaxy is blowing a pair of enormous gamma radiation bubbles spanning 50,000 light-years (magenta structures in the image above). This hourglass-shaped phenomenon was seen utilizing the Fermi Gamma-ray Space Telescope approximately 10 years ago, but its origin has actually stayed a mystery.
These radiation lobes are called Fermi bubbles, and they are covered with a couple of mystical bases of extremely brilliant gamma-ray emission. The Fermi cocoon, one of the brightest regions in the southern lobe (amplified inset in the image listed below), was as soon as thought to be the result of previous outbursts from the galaxys supermassive great void.
A global group of researchers co-led by former Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Researcher Oscar Macias (presently GRAPPA Fellow at the University of Amsterdam) and Australian National University Associate Professor Roland Crocker, and including Kavli IPMU Visiting Scientists Shunsaku Horiuchi and Shin ichiro Ando, analyzed information from GAIA and Fermi area telescopes to reveal that the Fermi cocoon is actually due to emission from the Sagittarius dwarf galaxy.
Figure 2. Gamma-ray image of the Fermi bubbles (blue) overlaid on a map of RR Lyrae stars (red) observed by the GAIA telescope. The shape and orientation of the Sagittarius (Sgr) dwarf match perfectly well those of the Fermi cocoon– an intense substructure of gamma-ray radiation in the southern part of the Fermi bubbles. This is strong evidence that the Fermi cocoon is due to energetic processes occurring in Sagittarius, which from our point of view, lies behind the Fermi bubbles. Credit: Crocker, Macias, Mackey, Krumholz, Ando, Horiuchi et al. (2022 ).
This satellite galaxy of the Milky Way is translucented the Fermi Bubbles from our position in the world (image 1). Due to its tight orbit around our Galaxy and previous passages through the stellar disk, it has actually lost many of its interstellar gas and a number of its stars have actually been ripped from its core into elongated streams.
Offered that Sagittarius was quiescent– with no gas and no excellent nurseries– there were just a few possibilities for its gamma-ray emission, including: i) a population of unknown millisecond pulsars or ii) dark matter annihilations.
Millisecond pulsars are remnants of specific kinds of stars, significantly more massive than the Sun, that remain in close double stars, today blast out cosmic particles as an outcome of their severe rotational energies. The electrons fired by millisecond pulsars collide with low-energy photons of the Cosmic Microwave Background moving them to high-energy gamma radiation.
The scientists showed that the gamma-ray cocoon might be discussed by millisecond pulsars in the Sagittarius dwarf, for that reason disfavoring the dark matter description.
Their discovery sheds light on millisecond pulsars as effective accelerators of highly-energetic electrons and positrons, and also recommends that similar physical procedures could be continuous in other dwarf satellite galaxies of the Milky Way.
” This is considerable because dark matter researchers have actually long thought that an observation of gamma rays from a dwarf satellite would be a cigarette smoking weapon signature for dark matter annihilation.”.
” Our research study forces a reassessment of the high energy emission abilities of quiescent excellent objects, such as dwarf spheroidal galaxies, and their function as prime targets for dark matter annihilation searches,” stated Macias.
Referral: “Gamma-ray emission from the Sagittarius dwarf spheroidal galaxy due to millisecond pulsars” by Roland M. Crocker, Oscar Macias, Dougal Mackey, Mark R. Krumholz, Shin ichiro Ando, Shunsaku Horiuchi, Matthew G. Baring, Chris Gordon, Thomas Venville, Alan R. Duffy, Rui-Zhi Yang, Felix Aharonian, J. A. Hinton, Deheng Song, Ashley J. Ruiter, and Miroslav D. Filipović, 5 September 2022, Nature Astronomy.DOI: 10.1038/ s41550-022-01777-x.
By Kavli Institute for the Physics and Mathematics of deep space
September 27, 2022