The Australian National University (ANU) researchers have discovered an alternate explanation for a strange gamma-ray signal originating from the center of the galaxy, which was long thought to be a hallmark of dark matter. Gamma-rays are the most energetic kind of electromagnetic radiation with the shortest wavelength.
Associate Professor Roland Crocker, a co-author of the paper, believes the gamma-ray signal, known as the Galactic Centre Excess, is caused by a certain sort of fast rotating neutron star, the super-dense stellar remnants of stars much more massive than our sun. The Galactic Centre Excess is an unusual abundance of gamma-rays that emerges from the center of our galaxy that has long perplexed astronomers.
“Our findings does not call the existence of the signal into question, but it does provide another potential source,” Associate Professor Crocker stated. “It is based on millisecond pulsars, which are neutron stars that spin 100 times per second.”
Pulsars are the remnants of huge stars that were destroyed in supernova explosions. The star’s core collapses into a whirling, squeezed ball of neutrons. They’re crammed into a region little more than 20 kilometers (12 miles) across. As it spins, the neutron star emits pulses of electromagnetic radiation from its poles. The term “pulsar” refers to a “pulsating radio source,” which perfectly describes these strange things. The best-known pulsar is at the heart of the Crab Nebula. It spins 30 times per second.
Our finding does not call the existence of the signal into question, but it does provide another potential source. It is based on millisecond pulsars, which are neutron stars that spin 100 times per second.
Associate Professor Roland Crocker
“Scientists had previously identified gamma-ray emissions from individual millisecond pulsars in the solar system’s vicinity, so we know these objects generate gamma-rays. Our model shows that the combined emission from a population of such stars, estimated to number approximately 100,000, would yield a signal completely compatible with the Galactic Centre Excess.”
The discovery may force scientists to reconsider where they hunt for signs concerning dark matter. “The nature of dark matter is completely unknown, so any potential indications generate a lot of interest,” Associate Professor Crocker said. “However, our findings suggest to another key source of gamma-ray production. For example, the gamma-ray signal from Andromeda, the next closest big galaxy to our own, may be primarily owing to millisecond pulsars.”
A millisecond pulsar spins exceedingly quickly, in less than 10 milliseconds. It emits electromagnetic radiation over the radio, X-ray, and gamma-ray spectrum ranges. These pulsars could have formed in low-mass X-ray binary systems. One of the members is a star, and the other is a black hole or neutron star. Millisecond pulsars are obvious candidates for gamma-ray emission sources since they are highly energetic things.
Crocker and his colleagues simulated the integrated radiation from around 100,000 such pulsars. It turns out that such a massive population can generate a signal akin to the Galactic Center Excess. He stated that they have not proven the existence of dark matter.
“Our findings suggest to another significant source of gamma-ray generation,” he explained. “For example, the gamma-ray signal from the Andromeda Galaxy could be mostly attributable to millisecond pulsars.”
The researchers examined the amount of the Galactic Center GeV Excess and the many proposed origins for it using gamma-ray data from the Fermi Large Area Telescope. They report on their investigation of millisecond pulsars in the center of the galaxy in their findings. They also talk about a strange kind of microwave “haze” in the Milky Way’s centre and the function these pulsars could play in its development.
The discovery that millisecond pulsars could play a significant part in the gamma-ray excess alters our understanding of dark matter’s involvement. For one thing, astronomers are still trying to figure out what this substance is. “The nature of dark matter is completely unknown,” Crocker remarked. “As a result, any potential clues generate a lot of interest.” With this new pulsar data, scientists may need to hunt for further hints to the existence of dark matter while attempting to explain its composition.
