Through Manisha Caleba† University of Sydney† Originally published on May 30, 2022 at The conversation†
Surprise! A slowly spinning neutron star
The discovery of a neutron star sending out unusual radio signals is rewriting our understanding of these unique galaxies.
My colleagues and I (the LakeTRAP team) made the discovery while observing the Vela X-1 region of the Milky Way about 1,300 light years away from the earth, using the MoreKAT radio telescope in South Africa. We saw a strange looking flash or “pulse” that lasted about 300 . lasted milliseconds†
The flash had some characteristics of a radio-emitting neutron star. But this was not like anything we had seen before.
Intrigued, we scoured older data from the region, hoping to find similar pulses. Interestingly, we identified more such pulses that were previously missed by our real-time pulse detection system (since we typically only look for pulses lasting around 20-30 milliseconds).
A quick analysis of the arrival times of the pulses showed that they repeat about every 76 seconds — while most neutron star pulses traverse within a few seconds or even milliseconds.
Our observation showed that PSR J0941-4046 had some of the characteristics of a pulsar or even a magnetic† Pulsars are the extremely dense remnants of collapsed giant stars that commonly emit radio waves from their poles. As they spin, the radio pulses can be measured from Earth, much like you would see a lighthouse flashing periodically in the distance.
However, the longest known rotation period for a pulsar before that was 23.5 seconds, meaning we may have found an entirely new class of radio-emitting objects. Our findings are: published May 30, 2022, in natural astronomy†
An anomaly among neutron stars?
Using all the data available to us from the MeerTRAP and ThunderKAT projects at MeerKAT we have managed to determine the position of the object with excellent accuracy. After this, we performed our more sensitive follow-up observations to study the source of the pulses.
The newly discovered object, called PSR J0941-4046, is a peculiar radio-emitting galactic neutron star that rotates extremely slowly compared to other pulsars. Pulsar pulse frequencies are incredibly consistent, and our follow-up observations allowed us to predict the arrival time of each pulse to a 100-millionth of a second.
Aside from the unexpected heartbeat, PSR J0941-4046 is also unique in that it is located in the “graveyard” of the neutron star. This is an area of space where we don’t expect any radio emissions at all, since the theory is that the neutron stars here are at the end of their life cycle and therefore inactive (or less active). PSR J0941-4046 challenges our understanding of how neutron stars are born and evolve.
It’s also fascinating because it appears to be producing at least seven distinctly different pulse shapes, while most neutron stars don’t show such variety. This diversity in pulse shape, as well as pulse intensity, is likely related to the object’s unknown physical emission mechanism.
A certain type of pulse exhibits a strong quasi-periodic structure, suggesting that some kind of oscillation drives the radio emission. These pulses can provide us with valuable information about the inner workings of PSR J0941-4046.
These quasi-periodic pulses bear some resemblance to enigmatic fast radio bursts, these are short radio bursts of unknown origin. However, it is not yet clear whether the PSR J0941-4046 emits the kind of energy seen in fast radio bursts. If we find this to be the case, it could be that PSR J0941-4046 is an “ultra-long period magnetar”.
magnetars are neutron stars with very powerful magnetic fields. Only a handful are known to broadcast in the radio portion of the spectrum† Although we have yet to identify an ultra-long-period magnetar, they are believed to be a possible source of fast radio bursts.
Lucky to spot it
It’s unclear how long PSR J0941-4046 has been active and broadcasting in the radio spectrum, as radio surveys typically don’t search that long.
We don’t know how many of these resources could be in the galaxy. Also, we can detect radio emissions from PSR J0941-4046 for only 0.5% of its rotational period, so it is only visible to us for a fraction of a second. Lucky we were able to spot it in the first place.
Tracking down comparable sources is a challenge. And that challenge means there may be a larger undetected population waiting to be discovered. Our finding also contributes to the possibility of a new class of radio transients: the ultra-long-period neutron star. Future searches for similar objects will be vital to our understanding of the neutron star population.
Manisha CalebaLecturer, University of Sydney†
This article was republished from The conversation under a Creative Commons license. Read the original article†
In short, the slow-spinning neutron star PSR J0941-4046 is testing our understanding of how neutron stars are born and evolve.
Source: Discovery of a radio-emitting neutron star with an ultra-long spin period of 76s
#EarthSky #Slowrotating #neutron #star #class #objects