Most neutron stars spin quickly, finishing a rotation in seconds or perhaps a fraction of a second. However astronomers have discovered one which takes its time, finishing a rotation in 54 minutes. What compels this odd object to spin so slowly?
When an enormous supergiant star explodes as a supernova, it leaves a collapsed core behind. The acute strain forces protons and electrons to mix into neutrons. Since they’re made virtually totally of neutrons, we name them neutron stars. These stellar remnants are extraordinarily small and very dense. Solely black holes have higher density.
As a result of conservation of angular momentum, neutron stars begin to spin quickly, usually rotating as quick as a number of hundred occasions per second. Astronomers have discovered greater than 3,000 radio-emitting neutron stars, and out of all of them, solely a really small quantity rotate slowly.
We normally detect neutron stars by their electromagnetic radiation and name them pulsars. Astrophysicists additionally name those with sluggish rotations long-period radio transients. There’s uncertainty round their sluggish rotation speeds and in the event that they’re even neutron stars, and probably the most not too long ago found one isn’t serving to take away the uncertainty.
In new analysis in Nature Astronomy, a group of researchers offered the invention of ASKAP J1935+2148, a long-period radio transient about 16,000 light-years away. The paper is “An emission-state-switching radio transient with a 54-minute period.” The lead writer is Dr. Manisha Caleb from the College of Sydney in Australia.
“Lengthy-period radio transients are an rising class of utmost astrophysical occasions of which solely three are identified,” the paper’s authors write. “These objects emit extremely polarized, coherent pulses of sometimes a couple of tens of seconds period, and minutes to roughly hour-long durations.”
Researchers have proposed totally different explanations for these long-period objects, together with highly-magnetic white dwarfs and highly-magnetic neutron stars referred to as magnetars. However the analysis group hasn’t reached a consensus.
ASKAP J1935+2148 has an especially lengthy interval of 53.8 minutes and three distinct emission states. Its brilliant pulse state lasts between 10 and 50 seconds, and its weaker pulse state, 26 occasions dimmer, lasts about 370 milliseconds. It additionally displays what’s referred to as a “quenched state” with no pulses.
Astronomers found the puzzling object by chance whereas observing an unrelated gamma-ray burst with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope in October 2022. The observations revealed ASKAP J1935+2148’s brilliant pulses of radio emissions. In about six hours of observations, the article emitted 4 brilliant pulses lasting from 10 to 50 seconds. Mild curve inspections and follow-up observations with the MeerKAT radiotelescope revealed the article’s whole pulsing sample.
“This discovery relied on the mixture of the complementary capabilities of ASKAP and MeerKAT telescopes in addition to the power to seek for these objects on timescales of minutes whereas finding out how their emission adjustments from second to second! Such synergies are permitting us to shed new gentle on how these compact objects evolve,” mentioned Dr. Kaustubh Rajwade, paper co-author and an Astronomer on the College of Oxford.
The three emission states, every totally different from the others, are puzzling. The researchers wanted to confirm that every sign from every state got here from the identical level within the sky. The truth that every sign had the identical time of arrival (TOA), as decided by each ASKAP and MeerKAT observations, signifies a single supply.
“What’s intriguing is how this object shows three distinct emission states, every with properties totally dissimilar from the others. The MeerKAT radio telescope in South Africa performed a vital position in distinguishing between these states. If the indicators didn’t come up from the identical level within the sky, we might not have believed it to be the identical object producing these totally different indicators.”
ASKAP detected the article’s sturdy, brilliant pulse mode, whereas MeerKAT detected its fainter, weak pulse mode. Each telescopes detected the quiescent mode.
“Within the examine of radio-emitting neutron stars, we’re used to extremes, however this discovery of a compact star spinning so slowly and nonetheless emitting radio waves was surprising,” mentioned paper co-author Ben Stappers, Professor of Astrophysics on the College of Manchester. “It’s demonstrating that pushing the boundaries of our search house with this new technology of radio telescopes will reveal surprises that problem our understanding.”
The character of the emissions and the speed of change of the spin durations strongly counsel that ASKAP J1935+2148 is a neutron star. Nevertheless, the researchers say they will’t rule out a extremely magnetized white dwarf. Since astrophysicists suppose that white dwarfs turn into extremely magnetized as binaries, and there aren’t any different white dwarfs close by, the neutron star clarification is extra probably.
The article’s radius additionally doesn’t conform to our understanding of white dwarfs. “Nevertheless, the implied radius is ~0.8? photo voltaic radii, main us to conclude that this supply can’t be anticipated by normal white-dwarf fashions,” the researchers clarify. White dwarfs are solely barely bigger than Earth, which appears to get rid of one because the potential supply.
Solely follow-up observations and extra devoted research can reveal the article’s true nature. Both means, whether or not it’s a white dwarf or a neutron star, the article will open one other window into the acute physics of both sort of object. Our understanding of each objects is barely a long time previous, so there’s certain to be tons left to find.
“It is crucial that we probe this hitherto unexplored area of the neutron-star parameter house to get a whole image of the evolution of neutron stars, and this can be an necessary supply to take action,” the authors conclude.
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