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02-15-2024

Glitching star explains cosmic radio bursts

Astronomers have been stumped by strange signals in the sky. These signals, called “fast radio bursts” (FRBs), are powerful bursts of radio energy that last only milliseconds, but release as much energy as the sun does in several months. 

However, the origins of FRBs remain a complete mystery. A team of scientists from NASA, RIKEN, and Kyoto University set out to solve the puzzle.

Focus of the study 

In 2020, a star called SGR 1935+2154 emitted FRBs that lasted for a fraction of a second. This event, called FRB 200428, was picked up by multiple telescopes and instruments.

Intrigued, the researchers decided to focus on this star which is about 20,000 light-years away. This isn’t just any star – it’s a “magnetar,” the leftover core of a giant star that exploded. It has a very strong magnetic field this is much stronger than anything we can make on Earth.

The scientists observed every aspect of this unique star. They tracked its spinning rate, analyzed the light it emitted, and even calculated its temperature.

Space telescopes

The study was based on observations from two powerful telescopes called NICER (Neutron star Interior Composition Explorer) and NuSTAR (Nuclear Spectroscopic Telescope Array). 

NICER is generally used for observing X-rays with energies between 2,000 and 8,000 eV. This is like the kind of light you might see from a hot, glowing gas. In contrast, NuSTAR specializes in detecting much higher energy X-rays, reaching up to about 79,000 eV.

For SGR 1935+2154, scientists used NICER to get detailed information about the lower-energy X-rays and NuSTAR to look for high-energy X-rays coming from different areas. They studied the detailed pattern of these bursts (called “pulse profiles”) and the different energies of the radiation (called “spectra”).

Magnetar glitches

SGR 1935+2154 was observed to have two sudden changes or “glitches” in its spinning speed. It sped up briefly, then slowed down quickly. This is kind of like when a bicycle wheel gets a big push and then spins really fast for a moment before slowing down again.

FRBs occurred between these two glitches. Scientists believe that an external force or event outside the magnetar must have given it a big push to make it spin so fast. It’s like the magnetic field itself might have experienced a disruption or distortion causing it to “snap back” and result in a sudden change in the magnetar’s spin behavior.

“Typically, when glitches happen, it takes the magnetar weeks or months to get back to its normal speed,” said Chin-Ping Hu, an astrophysicist at National Changhua University of Education in Taiwan and the lead author of the study. “So clearly things are happening with these objects on much shorter time scales than we previously thought, and that might be related to how fast radio bursts are generated.”

Powerful dynamics

Right before a big burst of energy (FRB),  the star let out a series of smaller bursts. This indicates a heightened state of activity. The magnetar’s appearance also seemed to change. Scientists took a close look at all the different emissions of light coming from the magnetar, both before and after the big burst.

They found clues that the specific area where the light was coming from changed quite often. The star’s temperature seemed to fluctuate as well. By studying its X-rays, scientists discovered that hot and cold spots kept appearing and disappearing constantly. These quick changes suggest powerful and dynamic events happening within the star.

Proposed theories

Based on theoretical models, scientists propose several theories. One of them is the presence of special fluids (superfluids) within the star that interact with its outer shell in a way that influences its rotation speed and causes the “glitches.”  

Additionally, the experts believe strong external winds impacting the magnetar from outside could affect these internal fluids, further influencing its rotation.

Study significance 

Peeking into magnetars and FRBs helps us understand the wildest corners of space. This knowledge benefits everyone, from revealing how stars live and die to understanding super-strong magnetic fields and matter behaving in ways we can’t recreate on Earth.

Magnetars act as extreme physics labs, letting us test our understanding of the universe’s basic rules under extreme conditions. This could lead to groundbreaking discoveries in fundamental physics, changing our view of the universe’s building blocks.

The mystery and vastness of space, with objects like magnetars and FRBs, ignite imaginations and inspire future scientists, engineers, and educators. 

The research is published in the journal Nature.

Image Credit: NASA Jet Propulsion Laboratory 

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