Something strange was found to be shining at the center of the Milky Way Galaxy, and scientists weren't sure of its origin. They now might have an answer.
Rather than being an indicator of dark matter, a bright patch of gamma radiation toward the center of our Milky Way Galaxy is caused by rapidly rotating stars in a neighboring galaxy. Invisibility is the hallmark of dark matter. Consequently, conventional sensors and detectors are unable to detect it because it emits no light or energy. Scientists believe that its composition is key to its elusive nature. Finding traces of it is of the essence for astrophysicists.
And one particular location towards the center of the Milky Way was a promising spot to search for its traces.
Hunting for Dark Matter
Toward the center of the Milky Way, a bright patch of gamma radiation has been discovered by an international team of scientists. Instead of being indicative of dark matter, the gamma-ray signal is caused by rapidly spinning stars in a neighboring galaxy. Based on data collected by the Fermi Gamma-ray Space Telescope, the study focused on two globe-shaped structures stretching over 50,000 light-years. These structures were initially discovered in 2010. Roland Crocker, a co-author of the study from The Australian National University (ANU), says that there are luminous regions within these Fermi bubbles.
Crocker said the Fermi cocoon, one of the brightest spots, is found in the southern bubble. A study shows that this bright patch originated from the Sagittarius dwarf galaxy rather than the galaxy’s supermassive black hole. “This is a galaxy that actually orbits the Milky Way and which, by chance, we view through the Fermi Bubbles from the Earth’s position. The fact that the Fermi cocoon overlaps the Fermi Bubbles is essentially a coincidence.”
As a result of the strong gravity of the Milky Way, most of the interstellar gas in the Sagittarius dwarf galaxy has been lost, and its stars have been ripped from its core. There are no stellar nurseries where gas and dust are compressed to form new stars. As a result, its gamma rays can only be explained by the destructive collisions of dark matter particles or by millisecond pulsars spinning rapidly.
Pulsars, cosmic lighthouses
It is more likely that millisecond pulsars are responsible for this emission from the Sagittarius dwarf than dark matter,” said Associate Professor Crocker. New insights into millisecond pulsar behavior have been revealed by the discovery. According to the findings, inactive galaxies like Sagittarius may be a source of gamma rays caused by millisecond pulsars. The experts added, however, that similar phenomena may also exist in other dwarf satellite galaxies of the Milky Way.
This finding is important because dark matter researchers believed that observations of gamma rays from dwarf satellites would be strong indicators of dark matter. It appears that this is not the case, but we’re still searching for dark matter signatures. We only assume dark matter exists because, without it, stars, planets, and galaxies simply wouldn’t behave the way they do. Over 80% of the universe’s (dark) matter has never been seen.
The study has been published in Nature Astronomy.
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