The Galactic Center Through Radio Wavelengths

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Recently astronomers surveyed the southern sky with the help of GLEAM for us to see the galactic center through radio wavelengths which are usually invisible.

The most thorough radio survey ever taken from the southern sky helped astronomers find the remains of dead massive stars that no one knew were there. In the meantime, it has also created some beautiful images.

It’s called GaLactic and Extragalactic All-sky MWA (GLEAM), an all-sky survey with the same resolution as the human eye-showing how the sky would look if you could see it through radio wavelengths. At radio wavelengths between 72 and 231 megahertz, the survey shows a whole passel o’ things that are usually invisible.

“It is the strength of this wide frequency range that helps us to disentangle various overlapping objects when we look at the complexities of the Galactic Center,” said astrophysicist Natasha Hurley-Walker of the node of the International Center for Radio Astronomy Research (ICRAR) at Curtin University, Australia.

“In fact, multiple objects have different ‘radio colors’, so we can use them to figure out what kind of physics is at play.”

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The orange streak in the middle of the picture (above) is the galactic plane and galactic center that shines brightly due to synchrotron radiation-electrons accelerating along spiraling magnetic field lines. The blue is where red light, such as the plasma around stars, is blocked. For a closer look here, you can explore an interactive website.

Such bubble-shaped blobs are remnants of supernova, left behind to scatter into space after a star has exploded. Such supernova remnants are believed to produce the high-energy electrons that generate synchrotron radiation; but to account for all the synchrotron radiation we see, there would have to be more supernova remnants out there than astronomers have so far discovered.

And, to try and find these missing explosions Hurley-Walker and her team conducted an investigation using the new GLEAM data update. Younger and nearby supernova remnants, or those in densely populated regions, are much easier to find. 295 of them are known to astronomers-so the team looked farther and in relatively empty regions.

The galactic center through radio wavelengths
The galactic center through radio wavelengths.
(Natasha Hurley-Walker/ICRAR/Curtin/GLEAM Team)

They found 27 previously unknown supernova remnants of massive stars, more than eight times the mass of the Sun. They even found a really young one in a particularly empty region of sky, where supernova remnants are really faint.

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“These are the remains of a star who died less than 9,000 years ago, meaning that at that time the explosion could have been visible to indigenous people across Australia,” said Hurley-Walker.

We know that aboriginal Australians have a rich history of 65,000-year-old astronomy, and their oral traditions still feature stars that differ in brightness. It is possible to describe this supernova in these ways, even though this is yet to be investigated.

The galactic center through radio wavelengths
The galactic center through radio wavelengths. View of the supernova that would have appeared 9,000 years ago. (Paean Ng/Astrordinary Imaging)

Three of the other known remnants occur in areas of the sky that do not have massive stars, which suggests that these previously ignored regions can be a source of hidden dead stars. Others were still very old-an exciting discovery, as supernovae are very hard to spot in this age range.

The Murchison Widefield Array, the radio telescope used to perform the observations in the Australian desert, is one of the few radio observatories in a “stable western country” that can observe between 80 and 300 megahertz frequencies without any interference.

It has also received a substantial upgrade recently. This means, the researchers wrote in their paper, more supernova remains could be found using the GLEAM survey, waiting to be discovered.

The research was published in the Publication’s of the Astronomical Society of Australia.


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