Astronomers have discovered the slowest spinning radio-emitting neutron star ever seen; It takes almost an hour to complete a full rotation.
That might sound pretty fast, but these dead stars are known to spin so fast that some make 700 full rotations each. second. Even the slowest of the nearly 3,000 radio-emitting neutron stars, or “pulsars,” discovered so far completes a full rotation in about one second.
However, this extremely slow neutron star, called ASKAP J1935+2148 and located 16,000 light-years from Earth, emits radio light at a rate so slow that it does not even fit current theories explaining the behavior of these dense stellar remnants.
“We are used to extremes in the study of radio-emitting neutron stars, but the discovery of a compact star that rotates so slowly and still emits radio waves was unexpected,” said Ben Stappers, a member of the research team. “Pushing the boundaries of our search space with these next-generation radio telescopes will reveal surprises that challenge our understanding.”
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Neutron stars age gracefully
Neutron stars, such as ASKAP J1935+2148, are born when the cores of massive stars, about eight to 10 times the mass of the Sun, run out of fuel required for nuclear fusion. This puts an end to the outward radiation pressure that has supported the star against the inward push of its own gravity for millions (sometimes billions) of years.
When this outward flow of energy is interrupted, the star’s core collapses, triggering a supernova explosion that destroys its outer layers and much of its mass. The net result is a stellar remnant between one and two times the mass of the Sun, compressed to about 12 miles (20 kilometers) across.
The hyperbirth of this neutron star forces electrons to collide with 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; which will weigh approximately the same as Mount. Everest But that’s not all. There is another extreme consequence of the collapse.
Just as an ice skater on Earth pulls his arms to increase his rotation speed 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 faster than other stars. blades of a blender.
Young neutron stars also have some of the strongest magnetic fields in the known universe, causing them to emit highly collimated radio waves from their poles. As these neutron stars rotate, their beams sweep across the universe, making pulsars look almost like lighthouses in the sky.
But as neutron stars age, their rotation slows and they can no longer power their lighthouse-like radio emissions. This is what makes ASKAP J1935+2148, first detected by the ASKAP radio telescope at the Murchison Radio-astronomy Observatory in Western Australia, so difficult to decode. This neutron star’s slow rotation indicates its advanced age, but somehow it still emits radio waves.
“The discovery of a neutron star candidate emitting radio pulses in this way is quite extraordinary. The fact that the signal is repeated at such a slow rate is extraordinary,” team leader Manisha Caleb from the Institute of Astronomy at the University of Sydney said in a statement. . “What is intriguing is how this object displays three different emission states, each with completely different properties from the others.”
The scientist added that the 64 radio antennas of the MeerKAT radio telescope in South Africa play a vital role in distinguishing these emission states.
“If the signals didn’t originate from the same point in the sky, we wouldn’t believe it was the same object producing these different signals,” Caleb continued.
The team still has urgent questions to answer about ASKAP J1935+2148; This includes the possibility that it is not a neutron star!
There is still the possibility that ASKAP J1935+2148 is actually a white dwarf, the type of compact stellar corpse left over when the core of a smaller star like the Sun dies. But to produce the kind of signal observed using the ASKAP and MeerKAT radio telescopes, this isolated white dwarf would have to have an extraordinarily strong magnetic field.
ASKAP Such objects have never been seen in the region of space occupied by J1935+2148. This means that this explanation does not fit the emissions of ASKAP J1935+2148 as much as it does a slowly rotating neutron star with extreme magnetic fields.
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However, further research will be needed to confirm the true nature of ASKAP J1935+2148 and 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 later stages of stellar evolution.
“This may prompt us to reconsider 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,” Caleb concluded.
The team’s research was published Wednesday, June 5, in the journal Nature Astronomy.