Astronomers have discovered the brightest radio pulsar outside our galaxy

When a star explodes and dies in a supernova, it takes on new life.

Pulsars are the extremely fast-spinning objects left over after massive stars have run out of fuel. They are extremely dense, with a mass similar to the sun squeezed into a region the size of a large city.

Pulsars emit beams of radio waves from their poles. As these beams sweep across the Earth, we can detect fast pulses hundreds of times per second. With this knowledge, scientists are always on the lookout for new pulsars inside and outside our Milky Way.

In research published this week in Astrophysical Journal, we detail our findings on the brightest radio pulsar ever discovered outside the Milky Way.

This pulsar, called PSR J0523-7125, is located in the Large Magellanic Cloud – one of our closest neighboring galaxies – and is more than ten times brighter than all other radio pulsars outside the Milky Way. It can be even brighter than those inside it.

Why wasn’t PSR J0523-7125 discovered earlier?

There are over 3,300 known radio pulsars. Of these, 99% reside in our galaxy. Many were discovered with CSIRO’s famous Parkes Murriyang radio telescope in New South Wales.

About 30 radio pulsars have been found outside our galaxy, in the Magellanic Clouds. So far we know of none in more distant galaxies.

Astronomers look for pulsars by looking for their distinct repeating signals in radio telescope data. This is a computationally intensive task. It works most of the time, but this method can sometimes fail if the pulse is unusual: such as too fast, too slow, or (in this case) if the pulse is too wide.

A pulse that is too broad reduces the “shimmering” signature astronomers look for and can make the pulsar more difficult to find. We now know that PSR J0523-7125 has an extremely wide beam and therefore escaped detection.

The Large Magellanic Cloud has been explored by the Parkes telescope several times over the past 50 years, and yet this pulsar has never been detected. So how do we find him?

An unusual object appears in ASKAP data

Pulsar beams can be highly circularly polarized, meaning the electric field of light waves rotates in a circular motion as the waves travel through space. These circularly polarized signals are very rare and are usually only emitted by objects with very strong magnetic fields, such as pulsars or dwarf stars.

We wanted to identify unusual pulsars that are difficult to identify with traditional methods, so we set out to find them by specifically detecting circularly polarized signals.

Our eyes cannot distinguish between polarized and non-polarized light. But the ASKAP radio telescope, owned and operated by the Australian national science agency CSIRO, has the equivalent of polarized sunglasses that can recognize circularly polarized events.

While analyzing data from our ASKAP Variables and Slow Transients (VAST) survey, a graduate student noticed a circular polarized object near the center of the Large Magellanic Cloud. Furthermore, this object changed brightness over the course of several months: another very unusual property that made it unique.

This was unexpected and exciting, as there was no known pulsar or dwarf star at this position. We think the object must be something new. We’ve observed it with many different telescopes, at different wavelengths, to try to solve the mystery.

In addition to the Parkes telescope (Murriyang), we use the Neil Gehrels Swift space observatory (to observe it at X-ray wavelengths) and the Gemini telescope in Chile (to observe it at infrared wavelengths). However, we didn’t detect anything.

The object could not be a star, as the stars would be visible in optical and infrared light. It was unlikely to be a normal pulsar, as the pulses would have been detected by Parkes. Even the Gemini telescope did not provide an answer.

Finally, we turn to the new, highly sensitive MeerKAT radio telescope in South Africa, owned and operated by the Radio Astronomy Observatory of South Africa. Observations with MeerKAT revealed that the source is indeed a new pulsar, PSR J0523-7125, rotating at a rate of about three rotations per second.

Below you can see the MeerKAT image of the pulsar with “sunglasses” polarized (left) and turned off (right). If you move the slider, you will notice that PSR J0523-7125 is the only bright object when the glasses are on.

Our analysis also confirmed its location within the Large Magellanic Cloud, about 160,000 light-years away. We were surprised to find that PSR J0523-7125 is more than ten times brighter than all the other pulsars in that galaxy, and possibly the brightest pulsar ever found.

What New Telescopes Can Do

The discovery of PSR J0523-7125 demonstrates our ability to find “missing” pulsars using this new technique.

By combining this method with the capabilities of ASKAP and MeerKAT, we should be able to discover other types of extreme pulsars and perhaps even other unknown objects that are difficult to explain.

Extreme pulsars are one of the missing pieces of the vast pulsar population picture. We will need to find more of them before we can really understand pulsars within the framework of modern physics.

This discovery is just the beginning. ASKAP has already completed its pilot research and is expected to reach full operational capability later this year. This will pave the way for even more discoveries, when the global network of SKA (square kilometer array) telescopes begins observing in the not-too-distant future.

This article is republished from The conversation under a Creative Commons license. Read the original article.

Image credit: Artist’s impression of PSR J0523-7125 in the Large Magellanic Cloud. Carl Knox, ARC Center of Excellence for Gravitational Wave Discovery (OzGrav), Author provided

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