by Astronomers have discovered the slowest pulsating radio-burst neutron star ever seen; it takes almost an hour to make a full rotation.
That may sound pretty fast, but these dead stars are known to spin so fast that each one has 700 full spins of experience. second. Even the faintest of the roughly 3,000 radio-emitting neutron stars, or “pulsars,” discovered so far complete a full rotation in a second or so.
However, this ultra-quiet neutron star, named ASKAP J1935+2148 and located 16,000 light-years from Earth, is emitting radio light at a rate too slow to match even current theories that describe the behavior of the This is a close stellar remnant.
“In the study of radio-emitting neutron stars, we are used to extreme conditions, but this discovery of a compact star spinning so slowly that is still emitting radio waves was unexpected,” Ben Stappers, a member of the team who behind the “It is being shown. Pushing the limits of our search space with this new generation of radio telescopes will reveal surprises that will challenge our understanding.”
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Neutron stars age gracefully
Neutron stars like ASKAP J1935+2148 are born when massive stars with about eight to 10 times the mass of the sun run out of the fuel needed for nuclear fusion within their cores. This eliminates the outward radiation pressure that, for millions (sometimes billions) of years, has been supporting the star against the inward pressure of its own gravity.
When this outflow of energy stops, the star’s core collapses, causing a supernova explosion that blows away the outer layers and most of its mass. The net result is a remnant constellation with between one and two times the mass of the Sun compressed to a width of just about 12 miles (20 kilometers).
The massive birth of this neutron star forces electrons to squeeze into their protons, creating a sea of neutrons so dense that if a tablespoon of the object’s material were brought to Earth, it would weigh as much as 1 billion tons — about the same weight as Mount. Everest. But that’s not all. The fall has another major consequence, too.
Just as an ice skater here on Earth draws in their arms to increase the speed at which they collapse due to conservation of angular momentum, the rapid reduction in the width of a stellar core means that young examples of these dead stars can spin more faster than the blender blades.
Young neutron stars also have some of the strongest known magnetic fields in the universe, causing them to emit highly collisional radio waves from their poles. As these neutron stars spin, the beams slide across the cosmos, causing pulses almost like celestial lighthouses.
However, as neutron stars age, their rotation slows down, and they can no longer power their lighthouse-like radio emissions. That’s what makes ASKAP J1935+2148, first seen with the ASKAP radio telescope at the Murchison Radio Astronomy Observatory in Western Australia, so challenging to decode. The slow rotation of this neutron star indicates an advanced age, but somehow, it is still emitting radio waves.
“It’s very unusual to discover a neutron star candidate emitting radio pulses in this way. It’s amazing that the signal is repeating at such a leisurely pace,” said team leader Manisha Caleb from the University of Sydney’s Institute of Astronomy in statement . “What’s interesting is how this object exhibits three distinct emission states, each with completely different properties from the others.”
The scientist also said that the 64 radio antennas of the MeerKAT radio telescope in South Africa played a crucial role in distinguishing between these emission states.
“If the signals didn’t originate from the same point in the sky, I wouldn’t believe it was the same thing producing these different signals,” Caleb continued.
The team still has pressing questions to answer about ASKAP J1935+2148, including the outer possibility that it may not be a neutron star at all!
There is still a chance that ASKAP J1935+2148 could be a white dwarf, the type of compact stellar body left behind when the core of a smaller, sun-like star dies. To produce a signal of the type observed using the ASKAP and MeerKAT radio telescopes, however, this remote white dwarf would have to have an extremely strong magnetic field.
Such objects have never been seen in the region of space occupied by ASKAP J1935+2148. This means that this explanation does not seem to fit the emissions of ASKAP J1935+2148 or a slowly spinning neutron star with extreme magnetic fields.
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However, more research will be needed to confirm the true nature of ASKAP J1935+2148 and to determine whether it is an outlaw white dwarf or a rule-breaking neutron star. Whatever the outcome, the results will challenge our understanding of the final stages of stellar evolution.
“It may even prompt us to rethink our decades-old understanding of neutron stars or white dwarfs, how they emit radio waves, and what their populations are like in our Milky Way galaxy,” said Caleb.
The team’s research was published on Wednesday (June 5) in the journal Nature Astronomy.
